Compendium Equine | September 2009

VOLUME 4 NUMBER 7 SEPTEMBER 2009

3 CE Contact Hours | CompendiumEquine.com | Peer Reviewed

Vol 4(7) September 2009

COMPENDIUM EQUINE CONTINUING EDUCATION FOR VETERINARIANS®

Managing Your Practice and Life FREE

CE

Cutting to Cure NEW C SERIES

P Proximal Suspensory S Desmitis of the Hindlimbs Photic Head Shaking

PAGES 289–336

Bo Read ok ing Pa R Ro ge ev om 30 ie 6 w

Refereed Peer Review

We’re for innovation.

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Only PreveNile® West Nile Virus vaccine utilizes chimera technology. Which is why PreveNile requires just one dose for primary(altrenogest) immunization – making it the perfect choice for foals and horses with unknown vaccination history as well as horses previously vaccinated with other West Nile vaccines.

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September 2009 Vol 4(7)

CompendiumEquine.com | Peer Reviewed | Free CE

The AAEP’s Media Partnership Program is composed of an esteemed group of industry-leading media outlets dedicated to providing resources and education, through the AAEP, to veterinarians and horse owners to improve the health and welfare of horses.

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EDITORIAL BOARD Michelle Henry Barton, DVM, PhD, DACVIM The University of Georgia Internal Medicine

EDITOR IN CHIEF James N. Moore, DVM, PhD Department of Large Animal Medicine College of Veterinary Medicine The University of Georgia Athens, GA 30602 706-542-3325 Fax 706-542-8833 jmoore@uga.edu

Gary M. Baxter, VMD, MS, DACVS Colorado State University Acupuncture, Surgery Jim Belknap, DVM, PhD, DACVS The Ohio State University Soft Tissue Surgery Bo Brock, DVM, DABVP (Equine) Brock Veterinary Clinic, Lamesa, Texas Surgery Noah D. Cohen, VMD, MPH, PhD, DACVIM (Internal Medicine) Texas A&M University Internal Medicine Norm G. Ducharme, DVM, MSc, DACVS Cornell University Large Animal

Compendium Equine is a refereed journal. Articles published herein have been reviewed by at least two academic experts on the respective topic and by the editor in chief.

290

Compendium Equine

Raymond J. Geor, BVSc, MVSc, PhD, DACVIM Michigan State University Metabolism, Nutrition, Endocrine-Related Laminitis Katharina Lohmann, MedVet, PhD, DACVIM (Large Animal) University of Saskatchewan Large Animal Robert J. MacKay, BVSc, PhD, DACVIM (Large Animal) University of Florida Large Animal Rustin M. Moore, DVM, PhD, DACVS The Ohio State University Surgery Debra Deem Morris, DVM, MS, DACVIM East Hanover, New Jersey Internal Medicine P. O. Eric Mueller, DVM, PhD, DACVS The University of Georgia Soft Tissue and Orthopedic Surgery

Susan C. Eades, DVM, PhD, DACVIM (Large Animal) Louisiana State University Large Animal

Elizabeth M. Santschi, DVM, DACVS The Ohio State University Surgery

Earl M. Gaughan, DVM, DACVS Littleton Large Animal Clinic Littleton, Colorado Surgery

Nathaniel A. White II, DVM, MS, DACVS Virginia Polytechnic Institute and State University Surgery

Any statements, claims, or product endorsements made in Compendium Equine are solely the opinions of our authors and advertisers and do not necessarily reflect the views of the Publisher or Editorial Board.

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September 2009 Vol 4(7)

Features 298

❯❯ C. Lyon In this ongoing series, we talk to equine practitioners from around the country about how they have found and maintained a work–life balance. ce.

CompendiumEquine.com | Peer Reviewed | Free CE

308

CE

Each CE article is accredited for 3 contact hours by Auburn University College of Veterinary Medicine.

Managing Your Practice and Life The Upside of Weekend Work: A Talk With Dr. Claudia Sandoval

FREE

NEW Cutting to Cure SERIES Proximal Suspensory D Desmitis of the Hindlimbs

CE

❯❯ Ferenc Tóth, Jim Schumacher, Michael Schramme, and Ger Kelly Learn about the diagnosis, treatment, and aftercare of this common cause of lameness in performance horses. Surgery may provide the best prognosis for return of full athletic function.

321

Abstract Thoughts Cells Arising From Monocytes: Nature’s Transformers ❯❯ David J. Hurley and James N. Moore This information can help you analyze the claims about vaccines and immune modulators and understand a horse’s immune response to these products.

327

Photic Head Shaking ❯❯ Bonnie R. Rush and Jason A. Grady The cause of head shaking is usually undetermined, but when natural sunlight is the cause, this condition is manageable. This article is presented in a quick-reference format, including diagnosis, treatment, and prognosis.

Departments 294 CompendiumEquine.com 296 Editorial: Cutting to Cure: A New Partnership With the ACVS ❯❯ Rustin M. Moore Cover image © 2009 Alexia Khruscheva/Shutterstock.com

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The AAEP’s Media Partnership Program is composed of an esteemed group of industry-leading media outlets dedicated to providing resources and education, through the AAEP, to veterinarians and horse owners to improve the health and welfare of horses.

292

Compendium Equine: Continuing Education for Veterinarians®

Calendar

Clinical Snapshot 302 Puncture Wound in a Thoroughbred Filly ❯❯ Joshua G. McNeil, Robert L. Linford, and Ann Rashmir-Raven

325 Dysphagia and Nasal Discharge in a Quarter Horse Gelding ❯❯ Adam Stern and Stephen Smith

306 Reading Room: Blackwell’s Five-Minute Veterinary Consult: Equine, 2nd edition 333 Product Forum 334 Market Showcase 334 Classified Advertising

319 Oral Bleeding and Swelling in a Quarter Horse Gelding

335 The Final Diagnosis: Nala and Me

❯❯ Michael Lowder

336 Index to Advertisers

❯❯ Amy I. Bentz

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WEB EXCLUSIVES

September 2009 Vol 4(7)

E-NEWSLETTERS

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WEB-EXCLUSIVE VIDEOS

❯❯ Head Shaking Videos These videos complement the article “Photic Head Shaking,” which begins on page 327.

SEARCHABLE ARCHIVES

Search all content since Compendium Equine’s launch in 2005. ❯❯ EEquineMail i M il hhelps l you prepare for questions from your clients by highlighting the latest topics from popularr publications for horse owners. In addition, links to related content in Compendium Equine are provided.

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❯❯ Eggs From Dead Mare Produce Filly ❯❯ AAEP Update on Equine Genetic Defects ❯❯ Obesity Link to Laminitis Deaths

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❯❯ E-mail your questions, suggestions, comments, or letters to the editor: editor@CompendiumEquine.com

RECOMBITEK®. For West Nile virus protection, the canary’s got your back all season long.

It’s good to have recombinant canarypox-vectored vaccine technology behind you.

RECOMBITEK® Equine West Nile Virus (WNV) vaccine is the only WNV vaccine made using this Unvaccinated Vaccinates Controls proven technology. This unique technology helps RECOMBITEK Equine WNV stimulate a fast10% 80% Clinical Signs (muscle acting1 immune response that lasts throughout mosquito season.2 (encephalomyelitis) fasciculation) RECOMBITEK Equine WNV is also the only commercially available vaccine that has been Fever 10% 90% Histopathology tested against natural challenge with WNV-infected mosquitoes2 as well as WNV intrathecal (mild to moderate 10% 80% encephalitis) challenge in horses (see table).3,* WNV Viremia 0% 100% In a study, 10 naive horses vaccinated with two doses of RECOMBITEK Equine WNV Horses were challenged two weeks after the second dose of vaccine on Days 0 and 35 were challenged by intrathecal administration — directly into RECOMBITEK Equine WNV. the spinal canal. Ten nonvaccinated control horses were likewise challenged. Eight of the 10 controls developed encephalomyelitis, attesting to the severity of the challenge, while a single vaccinated horse developed only muscle fasciculation.3 RECOMBITEK Equine WNV is safe for use in foals 2 months of age and older,4 and is labeled for annual revaccination with a single dose.**,5 Trust it for fast and lasting protection.

Intrathecal challenge results.†,3

†

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Siger L, et al. Assessment of the efficacy of a single dose of a recombinant vaccine against West Nile virus in response to natural challenge with West Nile virus-infected mosquitoes in horses. American Journal of Veterinary Research 2004;65(11):1459-1462.

Data on file at Merial. Study 02-092.

Siger L, Bowen R, et al. Evaluation of the efficacy provided by a recombinant canarypox-vectored equine West Nile virus vaccine against an experimental West Nile virus intrathecal challenge in horses. Veterinary Therapeutics 2006;7(3):249-256.

4 Data on file at Merial. Study 02-067.

5 RECOMBITEK Equine West Nile Virus vaccine product label.

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Editorial ❯❯ Rustin M. Moore, DVM, PhD, DACVS | The Ohio State University | Series Editor, Cutting to Cure rustin.moore@cvm.osu.edu

Cutting to Cure: A New Partnership With the ACVS

I

’m happy to introduce the new partnership including surgical options, indications, contrainbetween Compendium Equine’s Cutting to dications, and prognosis, so that practitioners can Cure surgical series and the American College offer their clients the best possible diagnostic and of Veterinary Surgeons (ACVS)! The inaugural treatment options for equine patients. article, “Proximal Suspensory Desmitis of the Before a Cutting to Cure article is written, the Hindlimbs,” starts on page 308. topic is approved by the ACVS. We encourage The overarching goal of this series readers to suggest surgical topics that would be is to provide equine practitioners of interest to most equine practitioners. If you with practical, accurate, and up-to- would like to suggest a topic or submit a paper date information regarding equine for the series, please contact Managing Editor diseases and conditions for which Kirk McKay at kmckay@vetlearn.com or 800surgery is a recommended or pos- 426-9119, ext 52434. At least one author of each sible therapeutic option. Therefore, paper must be an ACVS diplomate. before publication, all articles are We’re excited about this mutually beneficial peer reviewed by ACVS diplomates partnership between Compendium Equine and with experience and expertise in the ACVS. We encourage you to provide us with equine surgery. This approach helps constructive feedback on Cutting to Cure so that ensure that the information is clear, complete, we meet your needs and expectations and continand accurate as well as consistent with current uously advance equine health. We look forward thinking. to hearing from you. Enjoy this new series!

Cutting to Cure will address important diseases and conditions seen by equine practitioners.

SHARE YOUR COMMENTS When indicated, articles will provide step-by-step, Have something to say about this detailed descriptions and accompanying illustraeditorial or topic? Let us know: tions or photographs of the surgical procedure E-MAIL editor@CompendiumEquine.com so that it could be replicated by an appropriately experienced veterinary practitioner. Other articles FAX 800-556-3288 will focus on providing up-to-date information,

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Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

CE Calendar October 7–10 2009 ACVS Veterinary Symposium Marriott Wardman Park Hotel Washington, District of Columbia Phone 301-916-0200, ext. 300 Web www.surgicalsummit.org

October 12–15 Equine Biomechanics, Applied Anatomy and Gait Abnormalities Michigan State University East Lansing, Michigan Phone 707-884-9963 E-mail office@equinology.com Web www.equinology.com/info/course. asp?courseid=12

October 23–25 Theriogenology Lecture and Embryo Flush Wet Lab University of Georgia College of Veterinary Medicine Athens, Georgia Web www.vet.uga.edu/CE/conferences/ embryo.php

Only Adequan® i.m. (polysulfated glycosaminoglycan)

October 23–26 Principles of Saddle Fitting and Shoeing Dynamics

stimulates cartilage repair and reverses traumatic joint dysfunction

Winterbrook Ranch Murrieta, California Phone 707-884-9963 E-mail office@equinology.com Web www.equinology.com/info/course. asp?courseid=15

Within 48 hours

November 4–6 Diagnosis & Treatment of Lameness in the Horse Colorado State University Fort Collins, Colorado Phone 970-297-1273 Web www.cvmbs.colostate.edu/clinsci/ce

November 5–8 Reproductive Management and Artificial Insemination

the hyaluronic acid (HA) in the synovial fluid nearly doubles after a single injection.* Recommended dose: 5 mL every 4 days for 7 treatments intramuscularly.

To learn about the wear-and-repair of joints go to www.adequan.com.

Or call 800-974-9247 for a free video.

Colorado State University Equine Reproduction Lab Web www.csuequine.com

Keep joints in healthy balance

November 15–17 Annual Bluegrass Equine Symposium

There are no known contraindications to the use of intramuscular PSGAG in horses. Studies have not been conducted to establish safety in breeding horses. WARNING: Do not use in horses intended for human consumption. Adequan® i.m. brand Polysulfated Glycosaminoglycan (PSGAG). Caution: Federal law restricts this drug to use by or on the order of a licensed veterinarian. Each 5 mL contains 500 mg Polysulfated Glycosaminoglycan. Brief Summary Indications: For the intramuscular treatment of non-infectious degenerative and/or traumatic joint dysfunction and associated lameness of the carpal and hock joints in horses.

LUITPOLD PHARMACEUTICALS, INC. Animal Health Division, Shirley, NY 11967.

See product package insert for full prescribing information. *Burba DJ, Collier MA, Default LE, Hanson-Painton O, Thompson HC, Holder CL: IN VIVO KINETIC STUDY ON UPTAKE AND DISTRIBUTION OF INTRAMUSCULAR POLYSULFATED GLYCOSAMINOGLYCAN IN EQUINE BODY FLUID Compiled

by Benjamin Hollis; send TRITIUM-LABELED listings COMPARTMENTS AND ARTICULAR CARTILAGE IN AN OSTEOCHONDRAL DEFECT MODEL. The Journal of Equine Veterinary Science to bhollis@vetlearn.com.

1993; 696-703. Concentrations of Adequan i.m. in the synovial fluid begin to decline after peak levels are reached at 2 hours; then remain constant from 24 hours post injection through 96 hours. © 2008 Luitpold Animal Health. Adequan® is a registered trademark of Luitpold Pharmaceuticals, Inc. AHD 85201, Iss. 2/08 CE

Hagyard Equine Medical Institute Lexington, Kentucky Phone 859-255-8741 E-mail ntomlinson@hagyard.com Web www.hagyard.com Compiled by Benjamin Hollis; send listings to bhollis@vetlearn.com.

Compendium Equine | September 2009

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Managing Your Practice and Life SERIES EDITOR C. Lyon, VMD, Berwyn, Pennsylvania

The Upside of Weekend Work: A Talk With Dr. Claudia Sandoval Claudia Sandoval, DVM, of Fairfield Equine Associates in Newtown, Connecticut, has found a rewarding career in equine medicine that allows her to enjoy time with her husband and twin 6-year-old daughters.

Claudia with her husband, Ian Berke, and daughters, Criss and Ella.

When and where did you graduate from veterinary school?

Cornell University in 2007.

How did you find your current position?

I completed an internship at Woodside Equine Clinic in Ashland, Virginia, from 2007 to 2008 and then joined Fairfield Equine Associates in the summer of 2008. I found my position through a job posting on aaep.org asking for a doctor interested in weekend emergency duty and a 2-day workweek. By the time I applied, the posting had been removed because Fairfield Equine was unsure whether anyone would respond. I jumped at the position, realizing it was an opportunity to have

time with my daughters, work in an extraordinary practice, return to the Northeast to be closer to family, and do what I like most—wellness, dental, and internal medicine. In joining a practice predominantly focused on lameness, I felt that I could provide other valuable services and learn from the doctors’ experience with lameness and other areas in which I felt less adept.

Do you treat species other than equids?

No, only equids!

How many veterinarians are in the practice?

There are three partners, a board-certified surgeon, three associates, and two interns—nine total.

What is your work schedule?

Claudia performs a dental prophylaxis at Fairfield Equine Associates.

My schedule consists of three emergency weekends per month and wellness and dentistry work on Mondays and Fridays. This schedule allows me to spend time with my kids during the week.

Although I like emergency work, I can’t honestly say that I would have searched for a position like this if I didn’t have a family.

Are your colleagues supportive of your schedule?

Definitely. But, for my own sanity, I try my best not to have my family life interfere with my work.

What do you enjoy most about your job?

I love the variety. While I hear that most practitioners hate dealing with emergencies, several practitioners have told me that they like working up emergency cases, but they don’t like having to suddenly change their personal plans or having to go on calls after a tiring workweek. I don’t mind changes to my weekend plans, and I’m especially happy that I get to spend time with my

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Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

B:8.25” T:8” S:7”

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Federal law restricts this drug to use by or on the order of a licensed veterinarian. For use in horses only. Do not use in horses intended for food.

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Managing Your Practice and Life daughters and husband on weekdays.

What do you enjoy least about your job?

While I’m rarely asked to work midweek, sometimes I feel like I need to go in, especially if I have to check on cases, do paperwork, or make phone calls. To compensate for this, I dedicate a weekday to these tasks so that I’m less distracted by work when spending time with my family. This also gives me Claudia with LuLu, a donkey foal that had a slow start after birth but made up for lost time. the opportunity to go on calls with the more experienced doctors, which further improves my skills. While emergency cases can vary, I don’t see many lame horses, and I don’t want to lose the skills I acquired during school and my internship.

Do you have any hobbies?

I feel really lucky: I love my work and still get to spend time with my family.

I probably sound like a geek, but I enjoy my work so much that it feels like a hobby. If I’m not at work, I mostly focus on my kids. We enjoy activities at home, or I take them to the library, the park, or after-school activities. We purchased a house last year, so I’m working on several home-improvement projects. Before I had the twins, I was an avid runner, and I would love to return to the sport in the fall.

Have you struggled to find and maintain a balance between your work and personal life?

I think it’s always a struggle. It’s definitely easier now that my internship is finished. That year was so tough that it makes my current position seem easy to balance with family life. But I still run into snags, such as when horses are in the hospital, I’m following up a case, or the kids are sick. I’m lucky to have my husband, who is extremely supportive, and my colleagues, who are understanding and supportive.

How does your personal life affect your professional life?

It sort of feels like an escape in both directions.

Work can be a nice break from caring for my

300

kids. Likewise, when I’m frustrated at work (for example, when a client won’t pay a bill), it’s nice to go home to my family and escape— physically and mentally. The balance goes in waves: sometimes I feel like I’m not giving 110% to work, and sometimes work distracts me when I’m with my kids. Obviously, my family comes first, but I always strive to do my best work and continue learning. I’ve learned to accept my shortcomings as long as I’m doing my best for my patients and clients. I may not know everything, but I can certainly learn from each case for the future. This way, I feel like I’m striving to become a better clinician.

Do you have any advice for veterinarians interested in adjusting their work schedules or in changing practices to improve their work–life balance?

From speaking to other doctors, it sounds like equine medicine is slowly moving away from the mentality of working 24/7. There’s no harm in asking for a schedule change or whether your practice would support a position that you want to create for yourself. It certainly helps to work for a multidoctor practice that shares responsibilities and supports the personal lives of its staff.

I’m really lucky to have the support of Fairfield Equine Associates and to have had mentors and other veterinarians who helped me become successful and happy. It all started in veterinary school when I asked one of my professors how I could become an equine veterinarian. After developing friendships through my externships and internship, I began to understand that being an equine veterinarian doesn’t have to mean giving up your personal life. Because of my kids, I knew that I wanted a 4-day workweek, but I never imagined that I would find it so soon. I thought I would have to “pay my dues.” I feel really lucky: I love my work and still get to spend time with my family.

SHARE YOUR COMMENTS Have a question or comment about this article? Let us know: E-MAIL editor@CompendiumEquine.com FAX 800-556-3288 WEB CompendiumEquine.com

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

The best treatment for EGUS may be a dose of reality.

Equine Gastric Ulcer Syndrome (EGUS) caan easily become a reality for today’s horse. In fact, the majority of your clients’ racing and non-racing competittive horses could already be sufffering in silence with gastric ulcers.1,2 Clients come to o you for knowledge and tools they can’t get anywhere else. Training.

Experience. Diagnosis. Approved treatment. You havee the power to make the solution n for EGUS this simple.

Unique respon nse. Only ® GASTROGARD (omeprazole) is FDA-approved to treeat gastric ulcers.

Unique ability.. Only you have the ability to prrovide diagnoses and GASTTROGARD. For information and EGUS educational tools, taalk with your Merial Sales Representative today. Or call 1-888--MERIAL-1.

Response.Ability.

CAUTION: UTION: Federal llaw aw restricts restric icts this th drug to u use by or on the order of a licensed veterinarian. GASTROGARD is indicated for the treatment prevention of gastric ulcers in horses and foals 4 weeks and older. In efficacy trials, no adverse tment and prev vention o of recurrence rec g reactions in pregnantt or lactating mares has not been determined. DO NOT USE IN HORSES INTENDED tions were observed. obseerved. Safety Sa FOR HUMAN CONS CONSUMPTION. SUMPTI TI . KEEP THIS AND TION. AN ND ALL DRUGS OUT OF THE REACH OF CHILDREN. Mitchell RD. Prevalence of gastric ulcers in hunter/jumper and dressage horses evaluated for poor performance. Association for Equine Sports Medicine. September 2001.

Murray MJ. Endoscopic appearance of gastric lesions in foals: 94 cases (1987-1988). J Am Vet Med Assoc 1989;195(8):1135-1141.

1

2

®GASTROGARD is a registered trademark of the AstraZeneca Group of Companies. ©2008 Merial Limited. Duluth, GA. All rights reserved. EQUIGGD901-B (10/08)

See Page 302 for Product Information Summary

Clinical Snapshot Oral Paste for Horses and Foals NADA 141-123, Approved by FDA Caution Federal (USA) law restricts this drug to use by or on the order of a licensed veterinarian.

Description Chemical name: 5-Methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl) methyl]sulfinyl]-1H-benzimidazole.

Empirical formula: C17H19N3O3S. Molecular weight: 345.42. Structural formula: H3C

Case Presentation #1 ❯❯ Joshua G. McNeil, DVM Dixie Equine Medicine & Surgery Madison, Mississippi

OCH3 CH3 O

OCH3 H

How Supplied GASTROGARD® (omeprazole) Paste for horses contains 37% w/w omeprazole and is available in an adjustable-dose syringe. Each syringe contains 2.28 g of omeprazole. Syringes are calibrated according to body weight and are available in boxes of 7 units or 72 units.

Storage Conditions Store at 68°F – 77°F (20-25°C). Excursions between 59°F – 86°F (15-30°C) are permitted.

Indications For treatment and prevention of recurrence of gastric ulcers in horses and foals 4 weeks of age and older.

Dosage Regimen For treatment of gastric ulcers, GASTROGARD Paste should be administered orally once-a-day for 4 weeks at the recommended dosage of 1.8 mg omeprazole/lb body weight (4 mg/kg). For the prevention of recurrence of gastric ulcers, continue treatment for at least an additional 4 weeks by administering GASTROGARD Paste at the recommended daily maintenance dose of 0.9 mg/lb (2 mg/kg).

Directions For Use • GASTROGARD Paste for horses is recommended for use in horses and foals 4 weeks of age and older. The contents of one syringe will dose a 1250 lb (568 kg) horse at the rate of 1.8 mg omeprazole/lb body weight (4 mg/kg). For treatment of gastric ulcers, each weight marking on the syringe plunger will deliver sufficient omeprazole to treat 250 lb (114 kg) body weight. For prevention of recurrence of gastric ulcers, each weight marking will deliver sufficient omeprazole to dose 500 lb (227 kg) body weight.

• To deliver GASTROGARD Paste at the treatment dose rate of 1.8 mg omeprazole/lb body weight (4 mg/kg), set the syringe plunger to the appropriate weight marking according to the horse’s weight in pounds.

• To deliver GASTROGARD Paste at the dose rate of 0.9 mg/lb (2 mg/kg) to prevent recurrence of ulcers, set the syringe plunger to the weight marking corresponding to half of the horse’s weight in pounds.

• To set the syringe plunger, unlock the knurled ring by rotating it 1/4 turn. Slide the knurled ring along the plunger shaft so that the side nearest the barrel is at the appropriate notch. Rotate the plunger ring 1/4 turn to lock it in place and ensure it is locked. Make sure the horse’s mouth contains no feed. Remove the cover from the tip of the syringe, and insert the syringe into the horse’s mouth at the interdental space. Depress the plunger until stopped by the knurled ring. The dose should be deposited on the back of the tongue or deep into the cheek pouch. Care should be taken to ensure that the horse consumes the complete dose. Treated animals should be observed briefly after administration to ensure that part of the dose is not lost or rejected. If any of the dose is lost, redosing is recommended.

• If, after dosing, the syringe is not completely empty, it may be reused on following days until emptied.

Replace the cap after each use.

Warning Do not use in horses intended for human consumption. Keep this and all drugs out of the reach of children. In case of ingestion, contact a physician. Physicians may contact a poison control center for advice concerning accidental ingestion.

Adverse Reactions In efficacy trials, when the drug was administered at 1.8 mg omeprazole/lb (4 mg/kg) body weight daily for 28 days and 0.9 mg omeprazole/lb (2 mg/kg) body weight daily for 30 additional days, no adverse reactions were observed.

Precautions The safety of GASTROGARD Paste has not been determined in pregnant or lactating mares.

Clinical Pharmacology Mechanism of Action: Omeprazole is a gastric acid pump inhibitor that regulates the final step in hydrogen ion production and blocks gastric acid secretion regardless of the stimulus. Omeprazole irreversibly binds to the gastric parietal cell’s H+, K+ ATPase enzyme which pumps hydrogen ions into the lumen of the stomach in exchange for potassium ions. Since omeprazole accumulates in the cell canaliculi and is irreversibly bound to the effect site, the plasma concentration at steady state is not directly related to the amount that is bound to the enzyme. The relationship between omeprazole action and plasma concentration is a function of the rate-limiting process of H+, K+ ATPase activity/turnover. Once all of the enzyme becomes bound, acid secretion resumes only after new H+, K+ ATPase is synthesized in the parietal cell (i.e., the rate of new enzyme synthesis exceeds the rate of inhibition).

Pharmacodynamics: In a study of pharmacodynamic effects using horses with gastric cannulae, secretion of gastric acid was inhibited in horses given 4 mg omeprazole/kg/day. After the expected maximum suppression of gastric acid secretion was reached (5 days), the actual secretion of gastric acid was reduced by 99%, 95% and 90% at 8, 16, and 24 hours, respectively.

Pharmacokinetics: In a pharmacokinetic study involving thirteen healthy, mixed breed horses (8 female, 5 male) receiving multiple doses of omeprazole paste (1.8 mg/lb once daily for fifteen days) in either a fed or fasted state, there was no evidence of drug accumulation in the plasma when comparing the extent of systemic exposure (AUC0-∞). When comparing the individual bioavailability data (AUC0-∞, Cmax, and Tmax measurements) across the study days, there was great inter- and intrasubject variability in the rate and extent of product absorption. Also, the extent of omeprazole absorption in horses was reduced by approximately 67% in the presence of food. This is evidenced by the observation that the mean AUC0-∞ values measured during the fifth day of omeprazole therapy when the animals were fasted for 24 hours was approximately three times greater than the AUC estimated after the first and fifteenth doses when the horses were fed hay ad libitum and sweet feed (grain) twice daily. Prandial status did not affect the rate of drug elimination. The terminal half-life estimates (N=38) ranged from approximately one-half to eight hours.

Efficacy Dose Confirmation: GASTROGARD® (omeprazole) Paste, administered to provide omeprazole at 1.8 mg/lb (4 mg/kg) daily for 28 days, effectively healed or reduced the severity of gastric ulcers in 92% of omeprazole-treated horses. In comparison, 32% of controls exhibited healed or less severe ulcers. Horses enrolled in this study were healthy animals confirmed to have gastric ulcers by gastroscopy. Subsequent daily administration of GASTROGARD Paste to provide omeprazole at 0.9 mg/lb (2 mg/kg) for 30 days prevented recurrence of gastric ulcers in 84% of treated horses, whereas ulcers recurred or became more severe in horses removed from omeprazole treatment.

Clinical Field Trials: GASTROGARD Paste administered at 1.8 mg/lb (4 mg/kg) daily for 28 days healed or reduced the severity of gastric ulcers in 99% of omeprazoletreated horses. In comparison, 32.4% of control horses had healed ulcers or ulcers which were reduced in severity. These trials included horses of various breeds and under different management conditions, and included horses in race or show training, pleasure horses, and foals as young as one month. Horses enrolled in the efficacy trials were healthy animals confirmed to have gastric ulcers by gastroscopy. In these field trials, horses readily accepted GASTROGARD Paste. There were no drug related adverse reactions. In the clinical trials, GASTROGARD Paste was used concomitantly with other therapies, which included: anthelmintics, antibiotics, non-steroidal and steroidal anti-inflammatory agents, diuretics, tranquilizers and vaccines.

Diagnostic and Management Considerations: The following clinical signs may be associated with gastric ulceration in adult horses: inappetence or decreased appetite, recurrent colic, intermittent loose stools or chronic diarrhea, poor hair coat, poor body condition, or poor performance.

Clinical signs in foals may include: bruxism (grinding of teeth), excessive salivation, colic, cranial abdominal tenderness, anorexia, diarrhea, sternal recumbency or weakness. A more accurate diagnosis of gastric ulceration in horses and foals may be made if ulcers are visualized directly by endoscopic examination of the gastric mucosa.

Gastric ulcers may recur in horses if therapy to prevent recurrence is not administered after the initial treatment is completed. Use GASTROGARD Paste at 0.9 mg omeprazole/lb body weight (2 mg/kg) for control of gastric ulcers following treatment. The safety of administration of GASTROGARD Paste for longer than 91 days has not been determined.

Maximal acid suppression occurs after three to five days of treatment with omeprazole.

Safety • GASTROGARD Paste was well tolerated in the following controlled efficacy and safety studies.

• In field trials involving 139 horses, including foals as young as one month of age, no adverse reactions attributable to omeprazole treatment were noted.

• In a placebo controlled adult horse safety study, horses received 20 mg/kg/day omeprazole (5x the recommended dose) for 90 days. No treatment related adverse effects were observed.

• In a placebo controlled tolerance study, adult horses were treated with GASTROGARD Paste at a dosage of 40 mg/kg/day (10x the recommended dose) for 21 days. No treatment related adverse effects were observed.

• A placebo controlled foal safety study evaluated the safety of omeprazole at doses of 4, 12 or 20 mg/kg (1, 3 or 5x) once daily for 91 days. Foals ranged in age from 66 to 110 days at study initiation. Gamma glutamyltransferase (GGT) levels were significantly elevated in horses treated at exaggerated doses of 20 mg/kg (5x the recommended dose). Mean stomach to body weight ratio was higher for foals in the 3x and 5x groups than for controls; however, no abnormalities of the stomach were evident on histological examination.

Reproductive Safety In a male reproductive safety study, 10 stallions received GastroGard Paste at 12 mg/kg/day (3x the recommended dose) for 70 days. No treatment related adverse effects on semen quality or breeding behavior were observed. A safety study in breeding mares has not been conducted.

For More Information Please call 1-888-637-4251 and please visit our web site at www.gastrogard.com.

Marketed by: Merial Limited Duluth, GA 30096-4640 Merial Limited, a company limited by shares registered in England and Wales (registered number 3332751) with a registered office at PO Box 327, Sandringham House, Sandringham Avenue, Harlow Business Park, Harlow, Essex CM19 5QA, England, and domesticated in Delaware, USA as Merial LLC. US Patent: 4255431 and 5708017 Copyright © 2005 Merial Limited.

All rights reserved. Rev. 08-2005

❯❯ Robert L. Linford, DVM, PhD, DACVS Mississippi State University

❯❯ Ann Rashmir-Raven, DVM, MS, DACVS Michigan State University

A 2-year-old Thoroughbred filly presented with a puncture wound on the dorsal aspect of the right carpus (A and B). A small, full-thickness skin wound with swelling was present proximal to the right carpus, but no significant lameness was observed.

A

1. What are the potential complications

of a wound in this area?

2. What diagnostic steps are recom-

mended to assess the probability of complications?

3. What treatment is recommended?

SEE PAGE 304 FOR ANSWERS AND EXPLANATIONS.

B

SHARE YOUR PICTUREPERFECT CASES IN CLINICAL SNAPSHOT

Challenge your colleagues with a particularly intriguing or difficult case in Clinical Snapshot. Submit your photo(s) along with a brief case description, at least one test question, and detailed answers to each question posed. Each published submission entitles you to an honorarium of $100.

For more details, call 800-426-9119, extension 52434, or e-mail editor@CompendiumEquine.com.

®GASTROGARD is a registered trademark of the AstraZeneca Group of Companies.

302

Compendium Equine: Continuing Education for Veterinarians® | September 2009

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Clinical Snapshot Answers and Explanations Case Presentation #1

C

SEE PAGE 302 FOR CASE PRESENTATION.

1. The wound and associated soft tissue swelling are

immediately adjacent to the extensor carpi radialis tendon, the antebrachiocarpal joint, and the distal radius. Punctures or full-thickness skin wounds in this location may involve these structures, with potentially crippling lameness.

2. The wound should be carefully evaluated to determine whether it involves the adjacent joint, tendon sheath, or bony structures. If it does, aggressive treatment is warranted to reduce the potential for persistent lameness. The area is clipped, scrubbed with a topical antiseptic, and manipulated to determine whether exudate or synovial fluid can be expressed. If so, a culture is indicated. A sterile probe is used to gently assess the depth and extent of the wound and to determine whether a tract is present or deeper tissues are involved. Survey radiography, contrast radiography, and ultrasonography are also useful to check for involvement of underlying structures. In this case, a sterile probe was readily advanced proximally 6 cm within the wound. A small sterile catheter was then placed in the tract and used to administer 30 cc of sterile contrast media. The subsequent radiograph (C) documents the presence of contrast media in the extensor carpi radialis tendon sheath (oval), demonstrating penetration into the sheath.

3. Infections of the tendon sheath of the extensor carpi radialis have a much better prognosis than those of the flexor tendons. However, aggressive treatment should be administered to prevent septic tenosynovitis. Treatment of this horse included wound debridement, systemic antimicrobial therapy, regional limb perfusion with antimicrobials, and aseptic bandaging. The horse was sound throughout treatment and remained so after the wound had healed. Extensor tenosynovitis is an uncommon condition in horses, but it typically results in lameness. The lack of lameness in this case was likely due to early intervention and appropriate treatment.

SHARE YOUR PICTUREPERFECT CASES IN CLINICAL SNAPSHOT

304

Challenge your colleagues with a particularly intriguing or difficult case in Clinical Snapshot. Submit your photo(s) along with a brief case description, at least one test question, and detailed answers to each question posed. Each published submission entitles you to an honorarium of $100.

For more details, call 800-426-9119, extension 52434, or e-mail editor@CompendiumEquine.com

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

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Reading Room ❯❯ Reviewed by Amy I. Bentz, VMD, DACVIM, Veterinary Learning Systems, Yardley, Pennsylvania

T

HE SECOND EDITION of Blackwell’s FiveMinute Veterinary Consult: Equine, a hardcover reference text, is a must-read for veterinarians who want a quick refresher of pertinent facts about various equine diseases.

If you would like a quick-reference manual that provides pertinent equine information at your fingertips, this book is ideal.

Title: Blackwell’s Five-Minute Veterinary Consult: Equine, 2nd ed.

At the beginning of the book, is included for each disease/condithe contents are listed (1) in alpha- tion. The book concludes with a betic order, including specific dis- thorough index. ease names and broad topics (e.g., I highly recommend this book for “Anemia,” “Cough,” “Dystocia”), and veterinarians and veterinary students (2) by topic (e.g., “Behavior,” “Derm- who are looking for a concise text to atology,” “Ophthalmology,” “Respira- refresh their basic knowledge. If you tory,” “Urinary,” “Laboratory Tests,” would like a quick-reference man“Theriogenology,” “Toxicology”). ual that provides pertinent equine Throughout the book, diseases information at your fingertips, this and conditions are presented in book is ideal. It is also an excellent alphabetic order, with the disease/ reference text to take in the field condition name highlighted at the and should fit nicely in your front top of each page for ease of use. seat!

The information for each disease/condition is broken SHARE YOUR COMMENTS into the categories “Basics,” Have a question or comment about “Diagnosis,” “Treat ment,” this book review? Let us know: “Medications,” “Follow-up,” and “Miscellaneous.” This userE-MAIL editor@CompendiumEquine.com friendly format allows for FAX 800-556-3288 skimming or in-depth readWEB CompendiumEquine.com ing. A suggested reading list

Authors: Jean-Pierre Lavoie and Kenneth William Hinchcliff Publisher: Wiley-Blackwell Year: 2008 Pages: 874 ISBN: 978-0-8138-1487-2

TO LEARN MORE For further information about this book or to order a copy, visit

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306

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

SoundEklin_ Compendium/Compendium Equine.indd 1

7/6/09 3:05 PM

3 CE CREDITS

CE Article 1 C NEW SERIES

SERIES EDITOR Rustin M. Moore, DVM, PhD, DACVS The Ohio State University

At a Glance Diagnosis Page 308

Treatment Page 312

Surgical Technique Page 312

Aftercare Page 314

Prognosis Page 314

Proximal Suspensory Desmitis of the Hindlimbs ❯❯ Ferenc Tóth, DVM, Jim Schumacher, DVM, DACVS, University of Tennessee ❯❯ Michael Schramme, DVM, PhD, DECVS, North Carolina State University ❯❯ Ger Kelly, MVB, DECVS, O’Byrne and Halley Veterinary Hospital, Mortlestown County, Tipperary, Ireland Abstract: Proximal suspensory desmitis of the hindlimbs commonly affects performance horses.

Definitive diagnosis is usually achieved by the combination of clinical signs, diagnostic analgesia, and medical imaging. Conservative treatment, including stall rest followed by an incrementally increasing exercise regimen, with or without radial pressure-wave therapy, is often unrewarding. However, surgical intervention to interrupt the innervation of the suspensory ligament, with or without transection of the restricting fascia plantar to the suspensory ligament, may provide the best prognosis for return of full athletic function.

P

roximal suspensory desmitis (i.e., inflammation of the proximal aspect of the suspensory ligament) of the hindlimb is a cause of acute or chronic lameness in horses.1,2 It is most frequently diagnosed in horses 4 to 10 years of age that are used for dressage, general purpose competition, and eventing.3–5 Horses with excessively straight hocks or with hyperextended metatarsophalangeal joints seem to be predisposed to proximal suspensory desmitis of the hindlimbs.1 Thoroughbreds and Thoroughbred crosses appear to be more commonly affected.4 TO LEARN MORE The proximal aspect of the suspensory ligament is rigidly confined by Therapeutics in Practice: Treatment the plantar aspect of the Options for Hindlimb Proximal third metatarsal bone, the Suspensory Desmitis (September/ axial borders of the secOctober 2007) ond and fourth metatarsal Imaging Is Believing: Musculoskeletal bones, and the deep fascia Ultrasonography (September 2008) covering the suspensory ligament.1 These unique anRelated content on atomic features likely conCompendiumEquine.com tribute to the development

308

of proximal suspensory desmitis. Sensory and motor innervation of the suspensory ligament is provided by the deep branch of the lateral plantar nerve (DBLPN) and its branches—the medial and lateral plantar metatarsal nerves6 (FIGURES 1 AND 2). The tibial nerve supplies the lateral plantar nerve, from which the DBLPN originates.7 The DBLPN and plantar metatarsal nerves may be damaged when they are compressed due to an inflamed suspensory ligament.

Compression of these nerves may explain the poor response to treatment with rest alone of horses that are lame because of hindlimb proximal suspensory desmitis.8

Diagnosis Diagnosis of proximal suspensory desmitis of the hindlimbs is based on clinical signs, physical examination, regional analgesia of the proximal aspect of the suspensory ligament, ultrasonographic examination of the suspensory ligament and other structures on the plantar aspect of the metatarsus, and radiographic examination of the proximal aspect of the third metatarsal bone.1,3–6,9 Nuclear scintigraphy is unreli-

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

It is with great enthusiasm that I announce the new partnership between Compendium Equine’s Cutting to Cure surgical series and the American College of Veterinary Surgeons (ACVS)! The expertise and experience of ACVS Diplomates as authors and reviewers will add greatly to the value of this series by helping ensure that we provide practitioners with practical, accurate, and up-to-date information regarding equine surgery.

Rustin M. Moore, DVM, PhD, DACVS The Ohio State University The ACVS is proud to enter into this new cooperative venture with Compendium Equine and Series Editor Dr. Rustin Moore to complement the small animal effort previously launched under the guidance of Dr. Elizabeth Hardie. The ACVS is well known as a world leader in developing innovative surgical procedures and disease research.

Continuing education also is one of the pillars of the College. In addition to presenting at our yearly Symposium, ACVS Diplomates host and produce much of the continuing education in veterinary surgery in the United States. Now, with this collaboration, we are expanding our education outreach to a new level using both the small animal and equine venues of Compendium. The ACVS hopes you will enjoy and profit from our Diplomates’ contributions to this distinct continuing education effort.

Larry R. Bramlage, DVM, MS, DACVS Chair, ACVS Board of Regents To locate a diplomate, ACVS has an online directory that includes practice setting, species emphasis, and research interests (acvs.org/VeterinaryProfessionals/FindaSurgeon).

able in establishing a diagnosis of proximal suspensory desmitis.1 Hindlimb lameness caused by proximal suspensory desmitis is often characterized by a decreased arc of foot flight with a shortened cranial phase. Lameness is usually most obvious when the horse is ridden and is usually exacerbated in 85% of affected horses by flexion of the affected limb.8,9 Lameness improves substantially after anesthesia of the tibial nerve,

DBLPN, or lateral and medial plantar metatarsal nerves at the proximal aspect of the metatarsus or can improve after instillation of local anesthetic solution at the site of insertion of the suspensory ligament.1,4 Analgesia of the DBLPN is best achieved by inserting a needle 15 mm distal to the head of the fourth metatarsal bone and axial to the bone to a depth of 25 mm and injecting 2 to 4 mL of local anesthetic solution.7,8 Inadvertent injection of the tarsal sheath or the tarsometatarsal joint may cause falsenegative results.8 However, intraarticular analgesia of the tarsometatarsal joint occasionally alleviates lameness caused by proximal suspensory desmitis. Therefore, proximal suspensory desmitis should be considered as a cause of lameness if a horse suspected to be lame from osteoarthritis of the tarsometatarsal or distal intertarsal joint responds to diagnostic analgesia administered in the location described above but fails to respond to intraarticular medication, especially if radiographic examination reveals minimal changes in these joints.8 High-quality ultrasonographic images are helpful in the diagnosis of proximal suspensory desmitis of the hindlimb.6 The most common ultrasonographic abnormalities recorded in a study of 42 horses included diffuse reduction in echogenicity involving the dorsal border of the ligament in 23 horses, enlargement of the ligament in the median or transverse plane in 12 horses, and poor definition of the dorsal border in five horses.4 Other ultrasonographic changes associated with proximal suspensory desmitis include the presence of one or more hypoechoic areas, either centrally or peripherally, hyperechogenic foci, and irregularity of the plantar cortex of the third metatarsal bone.3,4 Combinations of these lesions are often seen. In addition, ectopic mineralization is more common in hindlimb suspensory ligaments than in the forelimbs; focal, anechoic areas are more commonly observed in the forelimbs.6 Recently, however, the value of ultrasonography in establishing the crosssectional area of the proximal aspect of the suspensory ligament has been questioned by demonstration of its poor correlation with measurements obtained using magnetic resonance imaging (MRI) and histology.10 When MRI was used as the gold standard to establish

CriticalPo nt Proximal suspensory desmitis of the hindlimbs is sometimes difficult to confirm by ultrasonographic examination of the ligament because of the surrounding bony structures.

CompendiumEquine.com | September 2009 | Compendium Equine: Continuing Education for Veterinarians®

309

FREE

CE Proximal Suspensory Desmitis of the Hindlimbs FIGURE 1

CriticalPo nt Radiographic abnormalities involving the proximal aspect of the third metatarsal bone are often associated with proximal suspensory desmitis.

The hindlimb of an equine cadaver showing the ramification of the lateral plantar nerve in the proximal plantar region of the metatarsus. The superficial and deep digital flexor tendons (1) have been transected and folded proximally and distally. The structures include the lateral plantar nerve (2), the deep branch of the lateral plantar nerve (DBLPN; 3), fibers of the DBLPN entering the suspensory ligament (4), the medial plantar metatarsal nerve (5), and the lateral plantar metatarsal nerve (6). (The distal portion of the limb is at the top of the photograph.)

a diagnosis of proximal suspensory desmitis, ultrasonography was found to have 90% sensitivity but only 8% specificity in diagnosing proximal suspensory desmitis.11 Radiographic abnormalities involving the proximal aspect of the third metatarsal bone are often associated with proximal suspensory desmitis. Common abnormalities observed in the lateromedial projection include alteration of trabecular orientation and new periosteal bone formation on the proximoplantar aspect of the third metatarsal bone. Trabecular sclerosis is frequently seen in the dorsoplantar projection.3 MRI was used successfully to identify proximal suspensory desmitis in the forelimbs of horses,12 and a recent report described MRI results evalu-

310

FIGURE 2

Cross-section of the left hindlimb, approximately 5 cm distal to the tarsometatarsal joint, of an equine cadaver showing the fascia (7) plantar to the suspensory ligament. (MTII, MTIII, MTIV = second, third, and fourth metatarsal bones, respectively; DDFT = deep digital flexor tendon; SDFT = superficial digital flexor tendon; SL = suspensory ligament; 5 and 6 = medial and lateral plantar metatarsal nerves, respectively)

ating the hindlimbs of 25 horses with proximal plantar metatarsal pain.11 Primary desmitis without osseous abnormalities was identified in six of the horses, primary desmitis with osseous abnormalities was identified in seven, and primary osseous abnormalities without desmitis were identified in eight. Four of the 25 horses had no obvious abnormalities. Lesions of the suspensory ligament identified during MRI included focal or generalized areas of signal hyperintensity, with or without enlargement of the cross-sectional area of the suspensory ligament, and adhesions between the plantar aspect of the third metatarsal bone and the dorsal surface of the suspensory ligament.11 These findings suggest that proximal suspensory desmitis is often associated with osseous disease, which may influence response to treatment and prognosis. Equine patients with pathologic changes at the interface of the suspensory ligament and the plantar aspect of the third metatarsal bone may have a worse prognosis for return to

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

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Madigan J and Pusterla N. Life Cycle of Potomac Horse Fever – Implications for Diagnosis, Treatment, and Control: A Review. AAEP Proceedings 2005;51:158-162.

Hamende V. Potomac horse fever cases confirmed in northern Wyoming. University of Wyoming Cooperative Extension Service. Press Release, September 13, 2002.

Available at http://wyovet.uwyo.edu/Diseases/2002/PotomacConf.pdf. Accessed February 18, 2008.

3 Merck Veterinary Manual. Ninth Edition. 2005:236-237.

4 Ryder E. Potomac Horse Fever Cases Popping Up in Ohio. TheHorse.com. Article #10013. July 15, 2007.

5 Marcella K. Conditions collide to propel PHF/Potomac horse fever must be treated rapidly to dodge fatalities. DVM, January 15, 2005.

Available at http://www.dvmnews.com/dvm/article/articleDetail.jsp?id=144082&pageID=1&sk=&date=. Accessed February 18, 2008.

6 Potomac Horse Fever. AAEP.org. Available at http://www.aaep.org/potomac_fever.htm. Accessed February 6, 2008.

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CE Proximal Suspensory Desmitis of the Hindlimbs soundness than patients with disease involving only the suspensory ligament.13

Treatment

CriticalPo nt Nonsurgical treatments (e.g., confinement, shockwave therapy) are often ineffective in resolving lameness due to proximal suspensory desmitis of one or both hindlimbs.

Treatment of equine lameness due to proximal suspensory desmitis of the hindlimbs has included restriction of exercise followed by a regimen of gradually increasing exercise.2,4 Although approximately 90% of horses with proximal suspensory desmitis of one or both forelimbs return to soundness with this treatment,14 most horses with proximal suspensory desmitis of one or both hindlimbs remain lame.2,4 In one study, only 6 of 42 horses with proximal suspensory desmitis of one or both hindlimbs treated with confinement followed by a regimen of controlled, gradually increasing exercise were able to return to their previous level of activity, without recurrent lameness, for more than a year.4 Compartment syndromea and associated neuropathy persist despite prolonged rest and may explain chronic pain and lameness associated with proximal suspensory desmitis. In people, abnormalities of the median nerve caused by entrapment may be permanent, adversely affecting the functional outcome of human patients undergoing surgical decompression of this nerve.15 Postmortem examination demonstrated evidence of peripheral nerve compression in 12 of 14 horses with proximal suspensory desmitis.8 These findings suggest that excision of a portion of the DBLPN, rather than decompression of the nerve alone, may be necessary to resolve lameness.

Treating horses with proximal suspensory desmitis of the hindlimbs with radial pressurewave therapy in addition to exercise restriction, improves their prognosis for return to soundness.5 In one study, 18 of 44 horses with proximal suspensory desmitis of one or both hindlimbs that received radial pressure-wave therapy in addition to restriction of exercise for 12 weeks were able to return to their previous level of activity for at least 6 months without recurrence of lameness.5 a Compartment syndrome results in ischemic neuropathy from compression of capillaries among the bundles of nerve fibers. The condition persists despite prolonged rest and may explain chronic pain and lameness associated with proximal suspensory desmitis.

312

Hewes and White2 reported that 85% of horses with lameness due to proximal suspensory desmitis of the hindlimbs characterized by core lesions and treated with desmotomy, fasciotomy, and exercise restriction for 30 days were able to return to full work. Other treatments for proximal suspensory desmitis include infiltration of a glucocorticoid around the insertion of the affected suspensory ligament of acutely affected horses,6 injection of bone marrow16 or bioscaffold material2 into the ligament, and systemic or local administration of glycosaminoglycans.2 Excision of a segment of the DBLPN to desensitize the suspensory ligament, either alone or combined with resection of the fascia plantar to the suspensory ligament to decompress the ligament, has been used by us and others17 to treat horses for lameness of one or both hindlimbs caused by proximal suspensory desmitis.

Surgical Technique The horse is anesthetized and positioned in dorsal recumbency with its hindlimbs flexed, and the area between the metatarsophalangeal joint and the crural region is aseptically prepared for surgery. A 6- to 8-cm longitudinal skin incision, centered at the level of the tarsometatarsal joint, is made at the lateral border of the superficial digital flexor tendon (FIGURE 3). A small stab incision is made through the flexor retinaculum and extended to the length of the cutaneous incision using scissors. The incision in the flexor retinaculum should be located 3 to 4 mm axial to the fourth metatarsal bone to provide sufficient tissue to easily suture the retinaculum.

The lateral plantar nerve is identified lateral to the superficial flexor tendon and retracted using a Penrose drain (FIGURE 4). After the flexor tendons have been reflected medially with retractors, either handheld or self-retaining, the DBLPN is located by bluntly dissecting areolar tissue dorsolateral to the deep digital flexor tendon. To perform fasciotomy, the deep digital flexor tendon is retracted medially, and the DBLPN is traced distally to the U-shaped proximal border of the fascia, which is located plantar to the suspensory ligament. The fascia is split longitudinally using scissors, and a 2-cm segment of the nerve is resected (FIGURES 5 AND 6). The incisions in the flexor retinaculum

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CE Proximal Suspensory Desmitis of the Hindlimbs FIGURE 3

CriticalPo nt Most horses with lameness of one or both hindlimbs due to proximal suspensory desmitis can be returned to soundness by resecting a portion of the deep branch of the lateral plantar nerve of the lame limb.

The hindlimb of an equine cadaver showing the skin incision over the lateral border of the superficial digital flexor tendon. A small nick (arrow) is present in the flexor retinaculum.

The needle is placed into the tarsometatarsal joint to show the relationship of this joint to the incision. (The distal portion of the limb is at the top of the photograph.)

and the subcutis are closed separately using 2-0 absorbable suture material in a continuous pattern. The skin is apposed using skin staples or nonabsorbable, 0-nylon or polypropylene suture in a vertical mattress suture pattern. The affected area is protected with a bandage.

Aftercare The affected limb should be rebandaged every 3 to 4 days until the sutures or staples are removed 14 days after surgery. An NSAID, usually phenylbutazone (2.2 mg/kg PO) or flunixin meglumine (1.1 mg/kg PO), is administered once or twice daily for 4 to 7 days. The patient is confined to a stall for 3 weeks but walked daily. After 3 weeks, the patient can be placed in a small paddock. Four to 8 weeks after surgery, the patient should be reexamined for lameness and the suspensory ligaments of the hindlimbs examined ultrasonographically.

The patient can gradually resume training 4 to 8 weeks after surgery if ultrasonographic

314

FIGURE 4

Figure 4. A hindlimb of an equine cadaver showing the location of the lateral plantar nerve (2) below the flexor retinaculum.

(The distal portion of the limb is at the top of the photograph.)

examination of the suspensory ligaments demonstrates no evidence of fiber disruption.

Prognosis Neurectomy, with or without plantar fasciotomy, appears to result in a better prognosis for return to soundness compared with treatment by confinement with gradual return to full exercise or treatment with radial pressure-wave therapy combined with restriction of exercise. In our practices, 102 horses underwent excision of the DBLPN without transection of the fascia plantar to the suspensory ligament without severe complications.

Follow-up data obtained at least 3 months after surgery revealed that 91 (89%) of these horses were able to return to their previous level of exercise without recurrence of lameness (unpublished data). In another study of horses with proximal suspensory desmitis of one or both hindlimbs, 214 of 271 horses (79%) that underwent both resection of a portion of the DBLPN and plantar fasciotomy of one or both hindlimbs were able to return to their previous level of exercise.13 Horses that had severe

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CE Proximal Suspensory Desmitis of the Hindlimbs FIGURE 5

1

CriticalPo nt In another study of horses with proximal suspensory desmitis of one or both hindlimbs, 214 of 271 horses (79%) that underwent both resection of a portion of the DBLPN and plantar fasciotomy of one or both hindlimbs were able to return to their previous level of exercise.

FIGURE 6

1

Blunt dissection between the deep digital flexor tendon (1) and the suspensory ligament of a cadaver using a curved mosquito forceps exposes the deep branch of the lateral plantar nerve (arrow). This nerve is elevated with the forceps and resected using a scalpel. The lateral plantar nerve is retracted laterally with a Penrose drain. (The distal portion of the limb is at the top of the photograph.)

The hindlimb of an equine cadaver showing transection of the fascia (7 ) plantar to the suspensory ligament. The lateral plantar nerve is retracted laterally using a Penrose drain, and the deep branch of the lateral plantar nerve is elevated using a mosquito forceps. The superficial and deep digital flexor tendons are held medially with a handheld retractor. (The distal portion of the limb is at the top of the photograph.)

ultrasonographic lesions of the suspensory ligament received an injection of bone marrow or xenogenic extracellular matrix (ACell Inc., Jessup, MD) into the lesions and underwent plantar fasciotomy and resection of a segment of the DBLPN. Of the 25 horses treated in this manner, 84% became sound. Horses with pain thought to be caused by insertional desmopathy (diagnosed when the lameness was not substantially affected by anesthesia of the DBLPN but was dramatically ameliorated after the origin of the suspensory ligament was infiltrated with local anesthetic solution) were treated by resection of a segment of DBLPN, plantar fasciotomy, and osteostixis of the proximal plantar aspect of the metatarsus.

Only 55% of these 35 horses returned to their

previous level of exercise after receiving this combination of treatments.13 The primary complication associated with the procedure is the failure to resolve lameness.

This may be due to either the presence of an additional DBLPN contributing to the innervation of the suspensory ligament7 or other conditions that may coexist before surgery or develop after surgery. Other complications of the surgery include incisional infection (our observation) and complete breakdown of the suspensory ligament (anecdotal reports). We have observed neither clinically appreciable changes in cutaneous sensation nor development of a painful neuroma after excision of a portion of the DBLPN, although the latter is a common complication of palmar digital neurectomy.18

References 1. Dyson SJ, Genovese RL. The suspensory apparatus. In: Ross MW, Dyson S, eds. Diagnosis and Management of Lameness in the Horse. Philadelphia: WB Saunders; 2002:654-672.

2. Hewes CA, White NA. Outcome of desmoplasty and fascioto-

316

my for desmitis involving the origin of the suspensory ligament in horses: 27 cases (1995-2004). JAVMA 2006;229:407-412.

3. Dyson S. Proximal suspensory desmitis: clinical, ultrasonographic and radiographic features. Equine Vet J 1991;23:25-31.

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

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CE Proximal Suspensory Desmitis of the Hindlimbs 4. Dyson S. Proximal suspensory desmitis in the hindlimb: 42 cases. Br Vet J 1994;150:279-291.

5. Crowe OM, Dyson SJ, Wright IM, et al. Treatment of chronic or recurrent proximal suspensory desmitis using radial pressure wave therapy in the horse. Equine Vet J 2004;36:313-316.

6. Dyson S. Proximal suspensory desmitis in the forelimb and the hindlimb. Proc AAEP 2000:137-142.

7. Hughes TK, Eliashar E, Smith RK. In vitro evaluation of a single injection technique for diagnostic analgesia of the proximal suspensory ligament of the equine pelvic limb. Vet Surg 2007;36:760-764.

8. Dyson S. Diagnosis and management of common suspensory lesions in the forelimbs and hindlimbs of sport horses. Clin Tech Equine Pract 2007;6:179-188.

9. McIlwraith CW. Diseases of joints, tendons, ligaments, and related structures. In: Stashak TS, ed. Adams’ Lameness in Horses.

5th ed. Philadelphia: Lippincott Williams & Wilkins; 2002:459-644.

10. Bischofberger AS, Konar M, Ohlerth S, et al. Magnetic resonance imaging, ultrasonography and histology of the suspensory ligament origin: a comparative study of normal anatomy of warmblood horses. Equine Vet J 2006;38:508-516.

11. Redding WR, Schramme M. Comparison of ultrasound and MRI in the diagnosis of proximal plantar metatarsal pain in 25

horses. Proc ACVS 2007:112-115.

12. Zubrod CJ, Schneider RK, Tucker RL. Use of magnetic resonance imaging to identify suspensory desmitis and adhesions between exostoses of the second metacarpal bone and the suspensory ligament in four horses. JAVMA 2004;224:1789, 1815-1820.

13. Bathe A. Plantar metatarsal neurectomy and fasciotomy for the treatment of hindlimb proximal suspensory desmitis. Proc ACVS 2007:116-117.

14. Dyson S. The suspensory apparatus. In: Rantanen N, Mckinnon A, eds. Equine Diagnostic Ultrasonography. Baltimore: Williams & Wilkins; 1998:454.

15. Hill S, Hall S. Microscopic anatomy of the posterior interosseous and median nerves at sites of potential entrapment in the forearm. J Hand Surg (Br) 1999;24:170-176.

16. Herthel DJ. Enhanced suspensory ligament healing in 100 horses by stem cells and other bone marrow components. Proc AAEP 2001:319-321.

17. Bathe A. Neurectomy and fasciotomy for the surgical treatment of hindlimb proximal suspensory desmitis. Proc Br Equine Vet Assoc Congr 2001:118.

18. Jackman BR, Baxter GM, Doran RE, et al. Palmar digital neurectomy in horses. 57 cases (1984-1990). Vet Surg 1993;22:285-288.

3 CE CREDITS

CE TEST 1 This article qualifies for 3 contact hours of continuing education credit from the Auburn University College of Veterinary Medicine. Subscribers may take individual CE tests online and get real-time scores at CompendiumEquine.com. Those who wish to apply this credit to fulfill state relicensure requirements should consult their respective state authorities regarding the applicability of this program.

1. What conformational hindlimb abnormality(ies) predispose(s) horses to proximal suspensory desmitis? a. excessively straight hocks b. sickle hocks c. hyperextended metatarsophalangeal joints d. a and c 2. Which imaging modality is the least reliable in confirming a diagnosis of proximal suspensory desmitis of the hindlimbs? a. ultrasonography b. radiography c. nuclear scintigraphy d. MRI 3. What is the most common ultrasonographic change associated with proximal suspensory desmitis of the hindlimbs? a. enlargement of the ligament on the median or transverse plane b. diffuse reduction in echogenicity c. poor definition of the dorsal border of the suspensory ligament d. diffuse mineralization of the ligament 4. Which radiographic abnormality is not seen with proximal suspensory desmitis of the hindlimbs? a. alteration of the orientation of trabecu-

318

lae on the proximal aspect of the third metatarsal bone b. new periosteal bone formation on the proximoplantar aspect of the third metatarsal bone c. trabecular sclerosis affecting the proximal aspect of the third metatarsal bone d. subchondral bone lysis affecting the proximal aspect of the third metatarsal bone 5. MRI has been used successfully to establish a diagnosis of proximal suspensory desmitis in a. forelimbs only. b. hindlimbs only. c. forelimbs and hindlimbs. d. none of the above 6. In one study, ____ of 44 horses with proximal suspensory desmitis of one or both hindlimbs that received radial pressurewave therapy in addition to restriction of exercise for 12 weeks were able to return to their previous level of activity for at least 6 months without recurrence of lameness. a. 12 c. 21 b. 18 d. 28 7. The suspensory ligament of the hindlimb is innervated by the a. DBLPN.

b. medial plantar metatarsal nerve. c. lateral plantar metatarsal nerve. d. all of the above 8. The lateral plantar nerve is a branch of the _________ nerve. a. tibial b. deep peroneal c. superficial peroneal d. lateral metatarsal 9. To resect a portion of the DBLPN, the clinician should center the skin incision a. 6 to 8 cm proximal to the tarsometatarsal joint. b. at the level of the tarsometatarsal joint at the lateral border of the superficial flexor tendon. c. 6 to 8 cm distal to the tarsometatarsal joint. d. close to the level of the tarsometatarsal joint at the medial border of the superficial flexor tendon.

10. In horses with lameness due to proximal suspensory desmitis of the hindlimbs, ____% returned to soundness after resection of a portion of the DBLPN without fasciotomy. a. 89 c. 55 b. 60 d. 41

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

Clinical Snapshot Particularly intriguing or difficult cases A

B

Case Presentation #2 ❯❯ Michael Lowder, DVM, MS The University of Georgia

A 29-year-old Quarter horse gelding presented with a history of acute weight loss, bleeding from the mouth, and swelling of the right mandible (A AND B). Two other veterinarians had seen the horse during the past 3 weeks. One veterinarian had extracted several teeth and administered antimicrobials and NSAIDs. The other veterinarian continued the treatment and biopsied an oral mass.

The histologic examination revealed

granulation tissue. The owner felt that the horse initially responded to the treatment. Oral examination revealed a large mass on the right mandible (C).

C

1. What is the primary differential based

on the history and examination?

2. What are the possible treatments?

SEE PAGE 320 FOR ANSWERS AND EXPLANATIONS.

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Answers and Explanations Case Presentation #2 SEE PAGE 319 FOR CASE PRESENTATION.

1. Neoplasia is the top differential for

a horse of this age with a history of acute weight loss, bleeding from the mouth, and no halitosis. The most common soft tissue oral tumor in a horse of this age is squamous cell

A

be successful in a small, localized tumor, but due to the extensive invasiveness of the tumor in this case, euthanasia was elected. The gelding had an ameloblastic carcinoma of the mouth, which is quite rare.

carcinoma. Other differentials may include tooth fracture, foreign body, hemangiosarcoma, myxomatous carcinoma, ameloblastic carcinoma, and basal cell carcinoma.

2. Surgical excision and radiation might

B

C

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Abstract Thoughts Highlighting scientific articles with important information relating to equine diseases

Cells Arising From Monocytes: Nature’s Transformers ABSTRACT * Dendritic cells have been considered an immune cell type

Series Editors ❯❯ David J. Hurley, PhD ❯e-mail djhurley@uga.edu ❯❯ James N. Moore, DVM, PhD

that is specialized for the presentation of Ag to naive T cells. Considerable effort has been applied to separate their lineage, pathways of differentiation, and effectiveness in Ag presentation from those of macrophages. This review summarizes evidence that dendritic cells are a part of the mononuclear phagocyte system and are derived from a common precursor, responsive to the same growth factors (including CSF-1), express the same surface markers (including CD11c), and have no unique adaptation for Ag presentation that is not shared by other macrophages.

The University of Georgia

CriticalPo nt

COM MEN TA RY

George Orwell, who had a dark vision of a narrowly controlled world in 1984, might have been surprised to know that some toys made that year were so flexible that they had more than one use. In 1984, toy manufacturer Hasbro released the first generation of Transformers—toys that could be twisted and turned to change form (e.g., a single toy could become a car, plane, or robot). What a concept! One toy could have multiple functional fates, depending on the needs of the child in charge. As it turns out, Transformers have a lot in common with monocytes.

(Perhaps screenplays for blockbuster monocyte movies are being considered in Hollywood right now.)

The article by Hume that we cite below reminds us (particularly those who conduct research about antigen presentation and inflammation) that cells arising from monocytes are very fluid and plastic in their functional capacities, which can be freely interchanged in vivo. During the past 10 to 15 years, the ability to force monocytes along a pathway toward a specific functional role by exposing them to specific cytokines in culture has led researchers to think more about the function of monocyte-derived cells in initiating and regulating the immune response. Laboratory workers can turn monocytes into a homogeneous population of cells with well-defined functional activities that can be studied in vitro.

Why did Dr. Hume feel the need to remind us that dendritic cells and macrophages are part of the same continuum of monocyte-derived cells? First, immunologists have been moving toward a new concept about how infections and vaccines induce immunity. Since the discovery that dendritic cells arise from monocytes with a distinctive morphology, a strongly expressed set of surface proteins that are associated with immune activation, and the ability to promote activation of T cells in culture systems, dendritic cells have been linked to the initiation of adaptive immunity. However, after care-

Dendritic cells and macrophages are not terminal end points but are functional states of cells that begin as monocytes.

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*Reprinted verbatim from Hume DA. Macrophages as APC and the dendritic cell myth. J Immunol 2008;181:5829-5835; with permission from Elsevier.

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Abstract Thoughts ful analysis of the data, no one has identified cellular phenotypes or a specific family of unique cytokines that separate dendritic cells and the other families of functional macrophages into distinct cell populations. Second, the published “history” of studies involving macrophages over the past 3 decades indicates that macrophages can act as antigen-presenting cells and that the function of antigen presentation is not only the domain of dendritic cells.

So why is Dr. Hume’s article important to equine veterinarians? First, it means that you now have another grain of salt with which to analyze the claims being made about vaccines and immune modulators.

If the fate of monocytes is plastic rather than fixed, this may help account for the short-term effects of these types of products. Second, a horse’s preexisting inflammatory state, environmental inflammatory and immune stimuli, and stress level all affect the strength and duration of immune responses to these products.

As you might expect, there is good news and bad news in all of this. On the positive side, horses have lots of “players” (essentially, all the cells that arise from monocytes) that can enhance a veterinarian’s attempt to arm the adaptive immune system and provide protection against disease. The bad news is that these players can be recruited to tissue and ordered to differentiate into cells with primary functions of managing microbial invasions and coordinating the repair of damaged tissue.

These activities can keep these players from presenting antigen and promoting further development of adaptive immunity. Overall, it means that the interactive system of control over the function of monocytes is in the “hands” of the cells in tissue. Thus, the tissue must be in charge of the overall outcome of how monocytes function.

Thus, monocytes are the ultimate “transformers” in nature. They sense the needs of the body by responding to the myriad signals released from individual cells in tissue and differentiating, as needed, to one of several functional forms. These forms support systems that control invaders and repair tissue damage by invaders and that drive long-term responses to invaders so that subsequent interaction will end more favorably for the body.

Monocytes not only are transformers but also are like people in Hollywood, whom Andy Warhol described as follows: “They’re beautiful. Everybody’s plastic, but I love plastic. I want to be plastic.” Monocytes are plastic in regard to their adaptability: they change form and function to serve the body over their relatively long lifetime. As Wayne Dyer, self-help author and speaker, said, “Transformation literally means going beyond your form.” By this definition, monocytes certainly undergo transformation.

CriticalPo nt The monocyte is a highly plastic and responsive cell. The fate of cells arising from monocytes is determined by the immediate problems they encounter in tissue. These cells change as problems in the tissue change.

September 2009 | Compendium Equine: Continuing Education for Veterinarians®

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Clinical Snapshot Particularly intriguing or difficult cases

Case Presentation #3

A

❯❯ Adam Stern, DVM

Stephen Smith, DVM Oklahoma State University

An approximately 10-year-old Quarter horse gelding presented with a history of chronic, intermittent dysphagia and nasal discharge. Examination of the oral cavity revealed poor dentition (missing teeth, multiple hooks, and a fractured molar tooth). The horse appeared to be adequately nourished, and no clinical abnormalities were noted on physical examination. Endoscopic examination revealed a moderate amount of purulent

SHARE YOUR PICTUREPERFECT CASES IN CLINICAL SNAPSHOT

material within the trachea and severe ulceration of a 15-cm segment of the esophagus. A photograph of the esophagus (A) was obtained at necropsy.

2. What risk factors are related to the

cause of this lesion?

3. How is this condition treated?

4. What are the possible complications?

1. What is your diagnosis?

SEE PAGE 326 FOR ANSWERS AND EXPLANATIONS.

Challenge your colleagues with a particularly intriguing or difficult case in Clinical Snapshot. Submit your photo(s) along with a brief case description, at least one test question, and detailed answers to each question posed. Each published submission entitles you to an honorarium of $100.

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325

Clinical Snapshot Answers and Explanations Case Presentation #3 SEE PAGE 325 FOR CASE PRESENTATION.

A

1. Based on the clinical examination

and necropsy results, a diagnosis of severe ulcerative esophagitis was made. The lesion was consistent with complications of an esophageal obstruction resulting in secondary pressure necrosis and mucosal ulceration. Common clinical signs of esophageal obstruction include nasal discharge containing ingesta, coughing, gulping, and excessive salivation.1 Less common signs include extension of the head and neck, sweating, and restlessness.

Based on the clinical findings of dysphagia and nasal discharge, the differential diagnosis includes guttural pouch diseases (e.g., mycosis, neoplasia), esophageal obstruction (e.g., foreign body, stricture, compression), temporohyoid osteoarthropathy, foreign bodies within the mouth or pharynx, strangles, and pneumonia. Although not suspected in this case, dysphagia can be seen in cases of rabies, botulism, leukoencephalomalacia (moldy corn toxicosis), and Centaurea solstitialis (yellow star thistle) toxicosis.

On necropsy, multiple pulmonary abscesses were noted, likely due to previous episodes of aspiration pneumonia. No significant findings were observed within the guttural pouches.

2. Risk factors for equine esophagea esophageal

obstruction include poor dentition, rapid ingestion of feed, poor quality of feed, inadequate water intake, and a history of choke. The patient in this case had poor dentition and a history of choke. Common sites of esophageal obstruction are the proximal esophagus, the thoracic inlet, the area overlying the base of the heart, or the area just cranial to the diaphragmatic hiatus.2 3. Treatment of acute choke includes administration of xylazine or detomidine in combination with acepromazine or butorphanol (to sedate the patient and relax the esophageal muscles).3,4 The cranial two-thirds of the esophagus consist of skeletal muscle; however, if the obstruction is in the distal one-third of the esophagus, which consists of smooth muscle, parenteral administration of oxytocin can help relax this muscle.

A stomach tube should be inserted with extreme care to avoid compli-

cations such as esophageal perforation. Refractory cases may require repeated lavage while the patient is either standing or in lateral recumbency. In more severe cases, surgical intervention may be indicated.

4. Possible complications secondary to esophageal obstruction include metabolic alkalosis due to prolonged loss of salivary sodium and chloride, formation of esophageal strictures or diverticula, recurrent esophageal obstruction, esophageal perforation, aspiration pneumonia, and pleuritis.

References 1. Feige K, Schwarzwald C, Furst A, Kaser-Hotz B. Esophageal obstruction in horses: a retrospective study of 34 cases. Can Vet J 2000;41:207-210.

2. Brown CC, Baker DC, Barker IK. Alimentary system.

In: Maxie GM, ed. Pathology of Domestic Animals. 5th ed. Edinburgh, UK: Elsevier Saunders; 2007:37-38.

3. Blikslager AT, Jones SL. Disorders of the esophagus.

In: Smith BP, ed. Large Animal Internal Medicine. 3rd ed.

St. Louis: Mosby; 2002:610-611.

4. Elce YA. Esophageal obstruction. In: Robinson NE, Sprayberry KA, eds. Current Therapy in Equine Medicine. 6th ed. St. Louis: Saunders; 2008:351-353.

Call for Papers Veterinary Therapeutics: Research in Applied Veterinary Medicine® is a quarterly journal dedicated to rapid publication.

h? researc n i d e v l invo Are you

We invite the submission of clinical and laboratory research manuscripts in small animal, large animal, and comparative medicine, including pathophysiology, diagnosis, treatment, and prognosis. Prospective, retrospective, and corroborative studies are all welcome. Submitted articles are scheduled to be published 90 to 120 days after acceptance.

Contact Cheryl Hobbs, 800-426-9119, ext 52408, or e-mail chobbs@vetlearn.com.

326

It’s not just therapeutics!

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

Feature

Photic Head Shaking* ❯❯ Bonnie R. Rush, DVM, MS, DACVIM ❯❯ Jason A. Grady, DVM, MS, DACVIM Kansas State University

At a Glance Diagnostic Criteria Page 327

Treatment Recommendations

H

ead shaking is a behavior in which horses toss their heads, rub their noses, snort, and/or sneeze in the absence of obvious external stimuli. Some horses head shake with such violence that they are dangerous to the handler or rider.

In a 1987 review of 100 head shaking horses, the cause was undetermined in nearly 90% of cases. In 1995, Madigan and coworkers presented a series of seven cases in which head shaking was triggered by natural sunlight, and darkness provided relief from the condition; this disorder is called photic head shaking.

Photic head shaking horses are suspected to experience a burning sensation or tingling of the muzzle (neuropathic pain) in response to bright sunlight.

Page 329

Differential Diagnosis Page 330

TO LEARN MORE

Prognosis Page 331

Understanding Behavior: Head Shaking (November/December 2008) To see a video of a horse with head shaking, go to the Web exclusives at CompendiumEquine.com *Updated by the authors and reprinted with permission from Standards of Care: Equine Diagnosis and Treatment 2001;1.1:1-4.

Related content on

CompendiumEquine.com

The mechanism of photic head shaking may be similar to photic sneezing in humans, in which exposure to bright light triggers sneezing episodes. Photic sneezing in humans is a heritable, nonallergic disorder. Photic head shaking may represent a form of referred pain in which stimulation of one of the cranial nerves enhances irritability of the other—in this instance, optic-trigeminal summation. This may be associated with convergence between optic and trigeminal tracts in the brainstem.

Therefore, neuropathic pain is the most plausible explanation for the signs associated with photic head shaking.

Bright sunlight is the most common trigger for neuropathic head shakers, but other stimuli, including specific feeds (as in gustatory head shaking), may also serve as a trigger for infraorbital nerve irritability.

Therefore, disorders other than neuropathic pain should be evaluated to eliminate other causes of this behavior. In some horses, the triggering stimulus cannot be identified; however, the head shaking seems to be characteristic of neuropathic pain, and affected patients respond to medical therapy.

Diagnostic Criteria Historical Information The condition affects adult horses. The mean age of onset is 7.5 to 9.2 years.

However, it has been documented in horses younger than 5 years.

CompendiumEquine.com | September 2009 | Compendium Equine: Continuing Education for Veterinarians®

327

Photic Head Shaking Findings are unremarkable in photic head shakers.

Horses with head shaking due to causes other than sunlight usually demonstrate intentional head tossing rather than rapid, vertical flips that resemble a reaction to a bee sting.

FIGURE 1

Laboratory Findings Complete blood count and serum chemistry analysis findings are unremarkable.

Endoscopic examination of the upper respiratory tract (including guttural pouches) and radiographic examination of the skull should be performed in all horses with head shaking to rule out temporohyoid osteoarthropathy, a foreign body, or traumatic injury. The results are unremarkable in horses with photic head shaking.

A commercial mask with protective lenses.

CriticalPo nt Horses may not exhibit the behavior during the examination; therefore, the owner should be asked to make a videotape of the head shaking before the appointment.

No breed predilection.

Geldings are overrepresented. Affected mares should be evaluated for ovarian dysfunction.

The absence of testicular or ovarian hormones may play a role in the pathophysiology.

Clinical signs are often seasonal, abating during the winter and returning in the spring.

The behavior is exhibited at rest and during exercise. Violent head shaking is common at the beginning of exercise.

Affected horses attempt to avoid direct sunlight by seeking shade or hiding their heads in unusual places.

Photic head shaking may begin after an upper respiratory tract infection.

Horses may not exhibit the behavior during the examination; therefore, the owner should be asked to make a videotape of the head shaking before the appointment.

Other Significant Diagnostic Findings To determine whether the behavior is induced by natural light, ideally, the clinician should subject the horse to the following: direct sunlight, blindfolding, the outdoors at night, and the application of dark eye lenses (FIGURE 1) in direct sunlight. The cessation of clinical signs during protection from direct FIGURE 2

Sudden, violent, jerking movements of the head in the absence of obvious external stimuli.

Characteristic quick vertical fl ips or jerking movements (as if stung by a bee on the end of the nose) may be interspersed with horizontal and rotary activity.

Affected horses often snort, sneeze, and rub their noses.

Ophthalmic, otic, and oral examinations should be performed to rule out other causes of head shaking.

328

Illustration by Felecia Paras

Physical Examination Findings

Infraorbital nerve block.

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

Photic Head Shaking sunlight indicates that light is a stimulus for head shaking.

Bilateral infraorbital nerve block (FIGURE 2; 10 mL of mepivacaine over and within the infraorbital canal) should be performed in horses with characteristic head shaking that does not respond to medical management. If nerve block results in the abatement of clinical signs, the diagnosis is confirmed.

Bilateral posterior ethmoidal nerve block (FIGURE 3; 5 mL of mepivacaine) using a 7-cm, 19-gauge spinal needle: the needle is inserted below the zygomatic arch and directed rostrally and ventrally toward the upper sixth cheek tooth (approximately 5 cm; FIGURE 4).

Differential Diagnosis See BOX 1.

Summary of Diagnostic Criteria for Photic Head Shaking Negative findings from otic, ophthalmic, oral, endoscopic (the upper airway, including the guttural pouches), and radiographic (skull) examinations.

Demonstration of sunlight-induced head shaking (sunlight may not be the only trigger for neuropathic head shaking).

Favorable response to a 7-day course of cyproheptadine and/or carbamazepine (see below).

FIGURE 3

Favorable response to bilateral infraorbital or posterior ethmoidal nerve block in horses that do not respond to cyproheptadine.

Treatment Recommendations Medical Therapy Cyproheptadine Cyproheptadine is an antihistamine and serotonin antagonist with anticholinergic effects.

The mechanism of action of cyproheptadine in treating photic head shaking is unknown.

Administer a 7-day course of cyproheptadine (0.3–0.6 mg/kg PO q12h) to determine response to therapy.

Horses that respond favorably should be treated with cyproheptadine during the season in which they exhibit head shaking.

Adverse effects include transient lethargy, depression, or anorexia.

Carbamazepine Carbamazepine (3–4 mg/kg PO q6–8h), which is labeled for treating trigeminal neuralgia in humans, may be administered alone or with cyproheptadine in horses that fail to respond to cyproheptadine alone.

CriticalPo nt Approximately 70% to 80% of photic head shakers respond favorably to cyproheptadine.

Some horses may respond initially but become more resistant to therapy.

Melatonin Melatonin (15–18 mg PO q24h administered between 5:00 and 6:00 PM) has reduced clinical signs in some horses.

Topical EMLA Cream Topical EMLA cream (AstraZeneca; lidocaine 2.5% and prilocaine 2.5%) may provide

Illustration by Mal Rooks Hoover

FIGURE 4

Diagram of the landmarks for a posterior ethmoidal nerve block.

Posterior ethmoidal nerve block. A 7-cm, 19-gauge spinal needle is inserted below the zygomatic arch and directed rostrally and ventrally toward the upper sixth cheek tooth.

CompendiumEquine.com | September 2009 | Compendium Equine: Continuing Education for Veterinarians®

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Photic Head Shaking Mechanical Techniques

Differential Diagnosis BOX 1

CriticalPo nt If sunlight has been identified as the stimulus of infraorbital pain, reduced sunlight exposure is indicated for untreated horses or horses that do not respond to medical or surgical management.

Temporohyoid osteoarthropathy: ❯ Proliferation of the stylohyoid bone— perform an endoscopic examination of the upper airway that includes the guttural pouches. ❯ Osteitis of the petrous temporal bone—perform a radiographic examination.

Foreign body, parasite, or infection in the external auditory canal—perform an otoscopic examination.

Oral pain (wolf teeth or diastema), oral ulceration, periodontal disease, periapical abscess—perform oral and radiographic examinations.

Iris cysts, uveitis, photophobia, retinal lesions—perform an ophthalmic examination.

Miscellaneous conditions: ❯ Guttural pouch mycosis, epiglottic entrapment—perform an endoscopic examination. ❯ Cervical pain—perform a radiographic examination of the cervical vertebrae. ❯ Trombicula autumnalis larval infestation (chiggers) of the muzzle— perform a skin scrape.

transient relief when applied to the muzzle.

Cover area with plastic wrap (make holes for nostrils). Leave on for 45 minutes.

Combination Treatment Cyproheptadine (as described above).

Magnesium supplementation (Quiessence, Foxden Equine, Stuarts Draft, VA).

Increases threshold for nerve depolarization and may reduce irritability of trigeminal nerve.

Administer 2 oz q24h PO. Increase to 4 oz q24h PO if no improvement.

Evaluate serum magnesium after 2 wk, then once monthly.

Spirulina Wafers (Springtime, Inc, Cockeysville, MD).

The mechanism is unknown, but they may increase the threshold for nerve depolarization and decrease irritability of the trigeminal nerve.

330

The use of a full-face net (covers ears to muzzle) or fly fringe or netting over the muzzle has reportedly been effective in controlling signs of head shaking. It is believed that the net or fringe over the muzzle provides a counterstimulant that may reduce responsiveness of the trigeminal nerve through receptor inhibition or adaptation.

A commercial face mask with eye protection can be applied to control clinical signs when the horse is saddled or turned out during daylight (FIGURE 1).

Surgical Intervention Bilateral infraorbital neurectomy is a salvage procedure for cases refractory to medical therapy. Surgical candidates must demonstrate a consistent response to serial infraorbital nerve blocks. Infraorbital neurectomy has been shown to be effective in eliminating signs of head shaking. However, clinical improvement is inconsistent and often only temporary. Postoperative complications may include nasal pruritus (common, temporary), reinnervation, and neuroma formation.

Bilateral sclerosis of the posterior ethmoidal branch of the trigeminal nerve is induced via perineural injection (5 mL) of 10% phenol in almond oil. In an anesthetized patient, insert a 20-cm styletted needle into the infraorbital canal to the level of the maxillary foramen; confirm needle location by fluoroscopy.

In a recent study on caudal compression of the infraorbital nerve in 24 horses, 16 of 19 horses had a successful outcome.1 The procedure requires specialized equipment, and the authors report that the technique needs refinement.

Patient Monitoring Horses should respond to cyproheptadine within 7 days.

If head shaking is well controlled, the dose of cyproheptadine may be decreased to 0.12 mg/kg PO q12h.

In many cases, medication may be discontinued during the winter.

Farm Management If sunlight has been identified as the stimulus of infraorbital pain, reduced sunlight

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

Photic Head Shaking exposure is indicated for untreated horses or horses that do not respond to medical or surgical management. Affected horses can be turned out at night or during overcast days.

If turned out during full sunlight, affected horses should have protection from the sun via a three-sided shed, trees, or a commercial face mask that provides eye protection.

Milestones/Recovery Time Frames Cyproheptadine Approximately 70% to 80% of photic head shakers respond favorably to cyproheptadine. Some horses may respond initially but become more resistant to therapy.

More than 80% of horses respond favorably to carbamazepine alone or in combination with cyproheptadine.

Relief from head shaking may be observed within 48 hours of initiation of therapy.

Clinical signs typically recur 24 hours after discontinuation of medical therapy.

Bilateral Infraorbital Neurectomy Approximately 30% to 40% of photic head shakers improve after this procedure.

Careful case selection (consistent response to infraorbital nerve block) may increase the likelihood of a positive postoperative outcome.

Nose Net Clinical signs of head shaking completely resolve in 25% to 30% of horses with the use of a nose fringe or netting that applies pressure to the skin over the muzzle.

Treatment Contraindications Administration of antihistamines, corticosteroids, or NSAIDs is unrewarding.

Intradermal skin testing followed by allergen-specific hyposensitization therapy is unsuccessful.

Prognosis Favorable Criteria Response to cyproheptadine within the first 7 days of treatment.

Unfavorable Criteria Failure to respond to recommended therapies.

Reference 1. Roberts VL, McKane SA, Williams A, Knottenbelt DC. Caudal compression of the infraorbital nerve: a novel surgical technique for treatment of idiopathic headshaking and assessment of its efficacy in 24 horses. Equine Vet J 2009;41(2):165-170.

Recommended Reading Cook WR. Head shaking in horses: an afterword. Compend Contin Educ Pract Vet 1992;14:1369-1372.

Lane JG, Mair TS. Observations on headshaking in the horse. Equine Vet J 1987;19: 331-336.

Madigan JE. In: Smith BP, ed. Large Animal Internal Medicine, 4th ed. St. Louis: Mosby; 2009:1044-1045.

Madigan JE, Bell SA. Characterisation of headshaking syndrome—31 cases. Equine Vet J Suppl 1998;27:28-29.

Madigan JE, Bell SA. Owner survey of headshaking in horses. JAVMA 2001;219(3):334337.

Madigan JE, Kortz G, Murphy C, Rodger L. Photic headshaking in the horse: 7 cases.

Equine Vet J 1995;27:305-311.

Mair TS. Assessment of bilateral infraorbital nerve blockade and bilateral infraorbital neurectomy in the investigation and treatment of idiopathic headshaking. Equine Vet J 1999;31:262-264.

Mair TS. Headshaking associated with Trombicula autumnalis larval infestation in two horses. Equine Vet J 1994;26:244-245.

Mair TS, Howarth S, Lane JG. Evaluation of some prophylactic therapies for the idiopathic headshaker syndrome. Equine Vet J Suppl 1992;11:10-12.

Mills DS, Cook S, Jones B. Reported response to treatment among 245 cases of equine headshaking. Vet Rec 2002;150: 311-313.

Mills DS, Cook S, Taylor K, Jones B. Analysis of the variations in clinical signs shown by 254 cases of equine headshaking. Vet Rec 2002;150(8):236-240.

Mills DS, Taylor K. Field study of the efficacy of three types of nose net for the treatment of headshaking in horses. Vet Rec 2003;152(2):41-44.

Newton SA, Knottenbelt DC, Eldridge PR. Headshaking in horses: possible aetiopathogenesis suggested by the results of diagnostic tests and several treatment regimens used in 20 cases. Equine Vet J 2000;32: 208-216.

Wilkins PA. Cyproheptadine: medical treatment for photic headshakers. Compend Contin Educ Pract Vet 1997;19:98-111.

Did You Know?

Infraorbital neurectomy was one of the earliest treatments for head shaking.a a Williams WL. Involuntary shaking of the head and its treatment by trifacial neurectomy.

Am Vet Rec 1899;23: 321-326.

CriticalPo nt More than 80% of horses respond favorably to carbamazepine alone or in combination with cyproheptadine.

CompendiumEquine.com | September 2009 | Compendium Equine: Continuing Education for Veterinarians®

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The Final Diagnosis ❯❯ Amy I. Bentz, VMD, DACVIM, Veterinary Learning Systems, Yardley, Pennsylvania

Nala and Me

F

ew things are more precious to large animal veterinarians than their canine copilots. They are faithful companions, ready to jump in the truck at a moment’s notice, whether it’s 7:00 AM or midnight. However, puppyhood can challenge even the most devoted dog lover. While watching the recent hit movie Marley and Me, I realized that, as a puppy, my Rhodesian ridgeback, Nala, occasionally surpassed Marley’s bad behavior.

When I graduated from veterinary school, my first two purchases were a jeep and a puppy that I named Nala. It took more than a year to obtain her from

Few things are more precious to large animal veterinarians than their canine copilots.

Share your weird or wondrous cases or anecdotes in The Final Diagnosis.

the busy breeder Alicia Mohr-Hanna.

When I first saw Nala, she was beautiful and peaceful, quietly lying in the grass, playing with a toy. I knew it would be a pleasure to take my new best friend home. As we were leaving, Alicia mentioned something about the puppy being the alpha female of the litter. Little did I

Nala as a puppy. (Courtesy of Brad C. Holmsten, DVM)

know how true that would turn out to be…

As my copilot, Nala was always ready to go on farm calls. She eagerly jumped in the truck, and we rode around the countryside, treating large animals. I quickly realized that Nala needed to be confined during farm visits because of job hazards (e.g., chasing barn cats and deer, wandering off). She would wait patiently in the truck, her keen, almondcolored sight hound eyes peering over the dashboard, watching the action. However, if she thought the call was taking

Every equine practitioner has at least one interesting, unusual, or funny story to share. Here’s your opportunity to amaze or amuse your colleagues. For examples of The Final Diagnosis, see CompendiumEquine.com or the last page of each issue.

Accepted submissions are published quickly, and authors receive an honorarium of $100.

E-mail submissions (no more than 650 words) to editor@ CompendiumEquine.com.

Nala at 2 years of age. (Courtesy of Steve Surfman) CompendiumEquine.com | September 2009 | Compendium Equine: Continuing Education for Veterinarians®

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The Final Diagnosis

too long, especially if there was too much conversation as the visit was ending, her patience would cease. She would hang her head out of the truck’s window and howl loudly, as only a hound can do. She was so loud, the owner and I wouldn’t be able to hear each other, which rapidly ended many visits. Nala would then happily settle down on the ride to the next farm. During a few very long farm calls, she resorted to chewing the passenger-side seatbelt, leaving it to dangle in shreds until I could replace it, which lightened my wallet by a few hundred dollars.

In addition, Nala was not a fan of staying in her crate. Although I spent many hours making beautiful, plush, waterproof beds for her and would crate her for only short periods, Nala enjoyed shredding countless beds.

I would find her surrounded by a pile of fluff with an innocent expression on her face.

When Nala was a puppy, taking her for a

“walk” was an adventure. I looked like a fisherman trying to reel in a marlin! Nala would jump around, trying to chase squirrels and deer, and it took all of my strength to not lose the leash.

Nala is 11 years of age now and has matured into a beautiful grand dame. Her job titles are now “chief security officer” and “correctional officer” to her two daughters, Peanut and Belle. However, despite Nala’s age, some of her antics continue. Nala has developed an amazing ability to steal food when my attention is briefly diverted by a phone call or a conversation. She waits quietly, stalking the treasure with her eyes, and then, at just the right moment, grabs the food and runs.

Instead of howling, she prefers to stare at me and make a very quiet, high-pitched call when she wants a treat. While Nala is not as agile as she used to be, sometimes she gets a gleam in her eye when she sees deer, and I know that they better run!

CriticalPo nt She would hang her head out of the truck’s window and howl loudly, as only a hound can do. She was so loud, the owner and I wouldn’t be able to hear each other, which rapidly ended many visits.

Index to Advertisers For free information about products advertised in this issue, e-mail the product names to productinfo@CompendiumEquine.com.

Company

Product

Page #

American Association of Equine Practitioners

55th Annual Convention

Inside back cover

American Association of Equine Veterinary Technicians and Assistants

AAEVT Membership

317

Bayer HealthCare Animal Health

Legend

299

BET Pharm

BioRelease Meloxicam LA

319

Dandy Products, Inc

Padding and Flooring

320

Equine Oxygen Therapy, LLC

Hyperbaric Treatment

323

Freedom Health, LLC

Succeed Equine Fecal Blood Test

Back cover

GLC Direct

GLC 5500

305

Intervet/Schering-Plough Animal Health

PreveNile

Inside front cover

Luitpold Pharmaceuticals, Inc

Adequan i.m.

297

Meds for Vets

Compounding Pharmacy

325

Merial

GastroGard

301, 302

IMRAB

291

Potomavac

311

RECOMBITEK

295

Platinum Performance, Inc

Platinum Performance Complete Joint

293

Purina

Equine Senior

303

Shank’s Veterinary Equipment

Surgery Tables

334

Sound-Eklin

Veterinary Imaging

307

Triple Crown Nutrition, Inc

Triple Crown Senior

313

Universal Ultrasound

MYLAB Ultrasound, UMS 900, TERAVET T3000

322

Veterinary Learning Systems

A Guide to Equine Joint Injection and Regional Anesthesia

324

Veterinary Therapeutics

326

VetLearn.com

332

82nd Annual Conference

315

Western Veterinary Conference

336

Compendium Equine: Continuing Education for Veterinarians® | September 2009 | CompendiumEquine.com

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