7 minute read
What Ails the Paws and Claws
from FVMA Advocate Issue 4, 2023
by FVMA
Linda Messinger | DVM, DACVD
Pododermatitis has many underlying causes and can present in a variety of ways in dogs and cats. Allergies are the most common cause of pododermatitis in dogs. Allergies can also be the cause of pododermatitis in some cats. Other causes of pododermatitis include infectious, immune-mediated, nutritional, neoplastic, idiopathic, and other causes. We will discuss several causes of pododermatitis in cats and dogs, along with diagnostics and therapies. The most common causes of nail disease will also be discussed.
ALLERGIES
Allergies, especially to airborne and food ingredients, are the most common cause of pododermatitis in dogs. Pedal pruritus tends to be the most common sign noted in dogs presenting with pododermatitis secondary to allergies. Secondary yeast and/or bacterial pododermatitis are common and can exacerbate pedal pruritus and dermatitis. Skin cytologies are most commonly used to determine the presence of yeast and/or bacteria on paws. Treating secondary infections and controlling the underlying allergy is important. If secondary infections continue to recur, then the allergy treatments need to be reassessed in addition to evaluating for possible other causes.
MITES
Mites (especially Demodex mites) and dermatophytosis can also cause pododermatitis. Demodicosis is typically diagnosed via deep skin scrapings/hair plucks. Dermatophytosis can be diagnosed via ringworm culture and/or PCR. Histopathology may also be helpful in diagnosing demodicosis and dermatophytosis. More recently, isoxazolines have been the mainstay for treating demodicosis. Given the high success rate of isoxazolines, trial treatments have also been performed by some. However, most dermatologists agree that it is best to perform diagnostics (deep skin scrapings/hair plucks) to better know what you are treating, especially as Demodex mites are usually easy to find when diagnostics are performed properly. This is especially true in immunocompromised patients where more isoxazoline treatment failures may be seen. Treatment should be continued until two to three consecutive negative skin scrapings/hair plucks are obtained. Underlying causes should be addressed when possible.
It is generally recommended that dermatophytosis be treated with a combination of topical and systemic antifungal agents in addition to environmental clean-up. Often, the recommended treatment goal is to obtain two consecutive negative dermatophyte cultures and/or PCR tests prior to discontinuing antifungal therapies. An excellent and free access resource is Diagnosis and Treatment of Dermatophytosis in Dogs and Cats by Moriello KA, Coyner K, Paterson S, Mignon B. Vet Dermatol 2017.
PAPILLOMAS
Papillomas can affect the paws. Those affecting the footpads can be challenging to treat. Diagnosis can be made by clinical presentation; histopathology can help confirm the diagnosis. Several treatments have been recommended including surgical excision, CO2 laser, and systemic and/or topical antiviral treatments (interferon, imiquimod). Spontaneous regression has been reported. Concurrently, controlling pain and discomfort is recommended, especially as these can feel like a persistent “rock in your shoe.”
IMMUNE-MEDIATED DISEASE
The most common immune-mediate disease that affects the feet in dogs and cats is pemphigus foliaceus. Other immunemediated diseases can also affect the paws. Immune-mediated diseases are typically diagnosed via multiple skin biopsies.
Immunosuppressive/immunomodulating therapies are most commonly recommended in the treatment of immunemediated diseases. Be sure to rule out drug reactions as a cause of immune-mediated dermatosis.
NUTRITIONAL CAUSES
Zinc-responsive dermatosis is likely the most common nutritional disorder to affect the paws of dogs. This is most commonly seen in Siberian Huskies and Alaskan Malamutes and is thought to be from a defect in zinc absorption. Biopsies/ histopathology are the preferred method of diagnosis. The mainstay of treatment is zinc supplementation.
INTERNAL CAUSES
It is believed that 90% of dogs with hepatocutaneous syndrome have footpad involvement. Liver changes and/or pancreatic glucagonomas are seen concurrently. Diagnosis is via multiple skin biopsies, although some may make the diagnosis clinically with classic footpad changes along with the classic “Swiss cheese” appearance of the liver on abdominal ultrasound and elevated liver enzymes on lab work. Treatment involves zinc, fatty acids, and protein/amino acid supplementation. Controlling secondary infections is also helpful, especially as secondary infection can increase patient pruritus and/or discomfort. Prognosis is generally considered poor.
CANCER
There are several types of cancer that can affect the paws, including primary lung tumors in cats that metastasize to their digits. Clinically, these cats may present with “infection” of the digits that are non- or partially responsive to antibiotics. Thoracic radiographs are recommended.
PLASMA CELL PODODERMATITIS
Plasma cell pododermatitis is a disorder of unknown etiology that usually affects multiple footpads in cats. The metacarpal and metatarsal footpads are most commonly affected. Diagnosis is based on clinical appearance and histopathology. Treatment recommendations include doxycycline, steroids, and cyclosporine-modified. Some have proposed surgical excision of the affected areas and others have suggested benign neglect.
INTERDIGITAL FOLLICULITIS AND FURUNCULOSIS (IFF)
Interdigital folliculitis and furunculosis (IFF) occurs most often in dogs who are short-coated, overweight, have anatomical changes, and/or may be secondary to allergies, hypothyroidism, demodicosis, etc.. IFF often starts as a sterile inflammatory process and progresses to papules and nodules that may rupture.
Secondary bacterial infections are common. Diagnosis is based on clinical presentation and breed. Evaluating for demodicosis and secondary bacterial (and yeast) infection is recommended. Histopathology is often helpful in confirming the diagnosis and ruling out other causes. Cultures are helpful in guiding antimicrobial therapy. Because these infections are deep, antibiotics are often recommended for at least six to eight weeks. Prednisone/prednisolone can be helpful in reducing inflammation. Long-term, cyclosporine-modified is generally recommended. Booties, light therapy, laser and/or surgery (fusion podopasty) may also be considered.
SYMMETRICAL LUPOID ONYCHODYSTROPHY (SLO)
Symmetrical lupoid onychodystrophy (SLO) is a common cause of nail disease, the cause of which is unknown. Often multiple claws on multiple paws are affected. The primary ruleouts are dermatophytosis and vasculitis. Checking the patient’s thyroid hormone status is recommended. In the past, biopsies were recommended for the diagnosis of SLO. Biopsies are no longer recommended if the clinical signs and signalment are compatible with SLO. However, biopsies are recommended if the patient fails treatment. The main treatment plan includes fatty acids, pain control, and pentoxifylline. Doxycycline and niacinamide are falling out of favor as we try to avoid using antibiotics in the long term.
LINDA MESSINGER DVM, DACVD
Dr. Linda Messinger is a practicing board-certified veterinary dermatologist at Apex Veterinary Specialty Services in the Denver metro area. She received both her Bachelor of Science and Doctor of Veterinary Medicine degrees from Cornell University. After veterinary school, Dr. Messinger completed a one-year small animal internship at the Animal Medical Center in New York City and then a dermatology residency at the University of Florida. Dr. Messinger has been board-certified by the American College of Veterinary Dermatology (ACVD) since 1993. She has lectured on veterinary dermatology to a variety of professional and lay groups, both internationally and nationally. She has been involved in several clinical trials, many of which were to help patients with allergies. In addition, Dr. Messinger is currently on the ACVD Program Committee which reviews all the abstracts for the North American Veterinary Dermatology Forum. She enjoys all areas of veterinary dermatology. Her pet family includes dogs, fish, and too many cats.
