Diagnosis of alopecia in dogs and cats by Grupo Asís

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DIAGNOSIS OF ALOPECIA in dogs and cats Servet (División de Grupo Asís Biomedia S.L.) Centro Empresarial El Trovador, planta 8, oficina I Plaza Antonio Beltrán Martínez, 1 • 50002 Zaragoza (España) Tel.: +34 976 461 480 • Fax: +34 976 423 000 • www.grupoasis.com

Ana Mª Ríos Boeta

The publishing strength of Grupo AsĂs Editorial Servet, a division of Grupo AsĂs, has become one of the reference publishing companies in the veterinary sector worldwide. More than 15 years of experience in the publishing of contents about veterinary medicine guarantees the quality of its work. With a wide national and international distribution, the books in its catalogue are present in many different countries and have been translated into nine languages to date: English, French, Portuguese, German, Italian, Turkish, Japanese, Russian and Chinese. Its identifying characteristic is a large multidisciplinary team formed by doctors and graduates in Veterinary Medicine and Fine Arts, and specialised designers with a great knowledge of the sector in which they work. Every book is subject to thorough technical and linguistic reviews and analyses, which allow the creation of works with a unique design and excellent contents. Servet works with the most renowned national and international authors to include the topics most demanded by veterinary surgeons in its catalogue. In addition to its own works, Servet also prepares books for companies and the main multinational companies in the sector are among its clients.

Diagnosis of alopecia in dogs and cats

DIAGNOSIS OF ALOPECIA in dogs and cats Ana Mª Ríos Boeta

AUTHOR: Ana María Ríos Boeta. FORMAT: 22 x 28 cm. NUMBER OF PAGES: 192. NUMBER OF IMAGES: 383. BINDING: hardcover.

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Alopecia in pets is a common reason for consultation. As all conditions affecting the skin, hair loss is usually striking and causes discomfort to pet owners, not only due to cosmetic reasons but also due to the consequences on their pet’s health. This book is intended as a highly visual guide on how to diagnose alopecia in dogs and cats, in a structured and methodical manner, based on the distribution pattern and lesions. The large number of images, diagrams, tables and drawings, coupled with clear and practical descriptions, will allow readers to make the most of this work in day-to-day dermatology consultations.

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Diagnosis of alopecia in dogs and cats

Presentation of the book It gives me great pleasure to present a unique book, Diagnosis of Alopecia in Dogs and Cats. It is rare to find a book that so well meets the expectations of veterinary clinicians while achieving an exquisite balance between text and images. The central topic of this book is an intriguing condition and a continuous source of diagnostic challenges for both dermatologists and general clinicians. Loss of hair is one of the most common reasons for pet dermatological consultations. Thanks to the body of research evidence accumulated over the last 15 years, these conditions can be approached using much more scientifically grounded diagnostic protocols than those used before the turn of the millennium. I am unaware of any other work dedicated exclusively to alopecia in dogs and cats. This magnificent text is written with exceptional clarity, and covers all aspects of the alopecic process, from the pathophysiological basis to diagnosis and therapy. Comprehension of the text is aided by the inclusion of well-designed schematics and graphics. The images included are another strong point, and have been specifically selected by the author, Dr. Ana RĂos, one of the greatest exponents of veterinary dermatology and pet internal medicine working in Spain today. This book is a clear reflection of her meticulous approach to her work. It is both highly practical and academically rigorous, precisely the characteristics necessary to provide a solid basis for the teaching of veterinary medicine. Congratulations Ana, and thank you for providing us with this beautifully written text. Colleagues, students, you have at your disposal an exceptional handbook on alopecia in dogs and cats, a book that will serve you well and allow you to identify the keys to the diagnosis of diseases of the skin and hair, thus ensuring professional success in your daily clinical practice. I am confident you will enjoy what you find inside.

Maite Verde Doctor of Veterinary Medicine at the University of Zaragoza Professor of Animal Medicine and Surgery AVEPA-accredited in Dermatology and Internal Medicine Chairperson of the Dermatology Group of AVEPA Former President of AVEPA

Diagnosis of alopecia in dogs and cats

The author Ana María Ríos Boeta Bachelor of Veterinary Science from the Universidad Complutense, Madrid. Doctor of Veterinary Sciences and Masters in Research Methodology in Health Sciences from Universidad Alfonso X el Sabio. Accredited in Dermatology by AVEPA (Spanish Association of Small Animal Specialists) and recipient of a Masters in Dermatology from the ESAVS (European School of Advanced Veterinary Studies). Coordinator of the Medicine and Surgery Service and Head of Dermatology in the Small Animal Unit, Veterinary Hospital of the Universidad Alfonso X el Sabio (Villanueva de la Cañada, Madrid).

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Ana Maria Ríos is a full member of the ESVD (European Society of Veterinary Dermatology), a founding member of GEDA (Specialist Dermatology Group of AVEPA), and has been a board member of AVEPA and president of the GEDA. She has also served as director of the scientific committee of AMVAC (Association of Companion Animal Veterinary Medicine, Madrid).

Communication services Website Online visualisation of the sample chapter. Presentation brochure in PDF format. AuthorÂ´s CV. Sample chapter compatible with iPad.

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DIAGNOSIS OF ALOPECIA in dogs and cats Ana Mª Ríos Boeta

Table of contents 1. Hair cycle and structure of the pilosebaceous unit in carnivores Introduction Anatomical segments and follicular structure

3. Diagnostic approach based on clinical signs Introduction Inflammatory focal and multifocal alopecia in dogs

Hair cycle

Generalised or diffuse noninflammatory alopecia in dogs

Haircoat colour and type in dogs

Focal and multifocal alopecia in cats

Haircoat colour and type in cats

Symmetrical alopecia in cats

References

2. Diagnostic methods. Microscopic examination of hair

4. Focal and multifocal inflammatory alopecia in dogs Introduction

Introduction

Focal and multifocal alopecia in dogs

Technique Normal hair

Focal and multifocal inflammatory alopecia of parasitic or infectious origin

Changes in hair composition and structure

Focal and multifocal inflammatory alopecia of autoimmune origin

Infectious and parasitic agents

Traumatic focal or multifocal inflammatory alopecia

Skin biopsy in alopecia Definition of clinical and histopathological lesions in cases of alopecia References

Focal or multifocal inflammatory alopecia of vascular origin Neoplastic focal and multifocal inflammatory alopecia Focal and multifocal inflammatory alopecia of nutritional origin References

Diagnosis of alopecia in dogs and cats

5. Focal and multifocal noninflammatory alopecia in dogs Hair cycle disorders Follicular destruction Keratinisation defects Follicular dysplasia and other hereditary forms of alopecia Alopecia due to malnutrition Excessive shedding References

6. Generalised noninflammatory alopecia in dogs Congenital and hereditary alopecia References

7. Self-induced alopecia in feline species Alopecia in cats Self-induced alopecia caused by pruritus Self-induced alopecia caused by behavioural disorders References

8. Spontaneous focal, multifocal, or diffuse alopecia in cats Alopecia due to follicular inflammation Congenital, atrophic, degenerative, and neoplastic processes and hair cycle disorders References

Appendix: Practical notes on canine and feline alopecia Classification of alopecia in dogs Inflammatory alopecia in dogs: diagnostic clues Noninflammatory alopecia in dogs: diagnostic clues Diagnostic protocol in dogs Classification of alopecia in cats Self-induced alopecia in cats: diagnostic clues Spontaneous alopecia in cats: diagnostic clues Diagnostic protocol in cats

DIAGNOSIS OF ALOPECIA in dogs and cats

Cortex Medulla Cuticle Huxley layer

Inner root sheath

Henle layer

Outer root sheath Basement membrane Fibrous sheath Hair matrix Melanocyte Follicular papilla Capillary

Figure 6. Structure of the hair bulb.

SPECIALISED HAIRS The outer root sheath is surrounded by two other structures: the basement membrane and a fibrous sheath. Mineralisation of the basement membrane has been described in miniature poodles, Bedlington terriers, and older dogs. The dermal papilla is a connective tissue located at the base of the follicle. This highly vascularised tissue is continuous with the dermal connective tissue and is covered by a thin layer of basement membrane. The dermal papilla is responsible for nourishing the proliferating cells of the matrix. The inner root sheath and the hair itself grow from a layer of epithelial cells known as the hair matrix, which covers the papilla and consists of basal keratinocytes and melanocytes. This layer plays a key role in both embryogenesis and the hair cycle, and reaches maximum and minimum volume in anagen and telogen phases, respectively. The keratinisation that occurs in the cells of the matrix differs to that seen in epidermal cells, and produces â&#x20AC;&#x153;hard keratinâ&#x20AC;?, a type of keratin rich in sulfur amino acids.

Two types of specialised hair are found in mammals: sinus or tactile hairs (vibrissae or whiskers), and tylotrich hairs.

Sinus hairs These are found on the muzzle, lips, eyelids, face, and throat, and on the palmar aspect of the carpus of cats. Sinus hairs are thick, straight hairs with a conical tip. They are characterised by the presence of a vascular sinus between the outer root sheath and the capsular connective tissue. The sinus is divided into an upper non-trabecular ring (annular) sinus and a lower cavernous (trabecular) sinus. A thickening of mesenchymal tissue projects into the annular sinus. The trabecular sinus contains many nerve fibres. Skeletal muscle fibres are attached to this type of follicle. Pacinian corpuscles, which act as mechanoreceptors, are located near the sinus hairs.

Tylotrich hairs These hairs are distributed between ordinary hairs all over the body. The corresponding follicles are larger and contain a single hair and an annular complex of neurovascular tissue surrounding the follicle at the level of the sebaceous gland. Tylotrich hairs are thought to act as rapidly adapting mechanoreceptors.

Hair cycle and structure of the pilosebaceous unit in carnivores

SEBACEOUS AND SWEAT GLANDS

HAIR CYCLE

The sebaceous glands of domestic animals are much more developed than those of humans, and sebaceous secretions are largely responsible for the lustrous and supple appearance of the skin of dogs and cats. The sebaceous glands are located next to the hair follicles, where their excretory ducts end. These glands are widely distributed throughout the body surface, except for the footpads and the nasal plane, and secrete a mixture of lipids consisting primarily of triglycerides and free fatty acids. Secretion is fundamentally regulated by hormones, and is stimulated by androgens and attenuated by corticosteroids.

The hair follicle undergoes a growth cycle consisting of sequential phases of growth (anagen), regression (catagen), rest (telogen), and shedding (exogen). Another phase (kenogen, during which the follicle is empty) may soon be added to this sequence (Fig. 7). In response to this cycle of activity, the portion of the hair located beneath the arrector pili muscle undergoes significant changes, including keratinocyte apoptosis and subsequent regeneration. Hair growth is influenced by multiple factors, including age, circadian rhythm, and photoperiod cycles, which in turn are mediated by the hypothalamus, hypophysis, and pineal gland, altering levels of various hormones (e.g. melatonin, prolactin, and gonadal, thyroid, and adrenal hormones) (Table 1).

Epitrichial or apocrine sweat glands are distributed across the body surface, except for the footpads and the nasal plane. They are located below the sebaceous glands and their excretory duct ends in the isthmus of the follicular canal. These glands secrete a lipid suspension that mixes with sebum.

Catagen phase

Epidermis

Dermis Subcutaneous tissue

Late anagen phase

Hair

Telogen phase

New hair 1

Shedding of old hair

2 3

Figure 7. Schematic showing

hair cycle in dogs and cats. After the telogen phase, the hair follicle may shed the hair shaft and enter kenogen phase for an indefinite period of time, or alternatively progress directly to the anagen phase. Shedding of the dead shaft (exogen phase) can occur at any point during the next cycle, but tends to occur during anagen phase.

Exogen phase Kenogen phase

Old hair Early anagen phase

Empty follicle

1 2 3

Initiation of new hair growth

1 2 3

DIAGNOSIS OF ALOPECIA in dogs and cats

Table 1. Substances that affect the hair cycle. Substances

Stimulators of the hair cycle

Hormones

■■ ■■ ■■ ■■ ■■

Growth factors

■■

■■ ■■ ■■

■■

Thyroid hormones Corticotropin (ACTH) Melatonin Androgens Growth hormone Fibroblast growth factor 7 (FGF-7) Hepatocyte growth factor Insulin growth factor Keratinocyte growth factor, WNT, β-catenin, TGF-α Glial cell line-derived neurotrophic factor (GDNF)

Cytokines

Substance P

Others

■■ ■■ ■■

Cyclosporine Minoxidil Finasteride

The hair cycle involves the repeated induction of the anagen phase and the consequent growth of the hair through the dermis. The specific factors that mediate the induction, progression, and regression of the anagen phase are unknown, although multiple growth factors and their receptors (EGF, TGF-β1, TFG-β2) have been identified in the follicle and the adjacent mesenchyme. These factors control cell proliferation, collagenase production, and the action of macrophages during the hair cycle. During the hair cycle these factors, through contact with mast cells, induce changes in cutaneous innervation, substance P levels, and the sensory and autonomic innervation of the hair follicle. The hair follicle is also a source and a target of neurotrophic substances. Accordingly, the hair cycle can be altered by neuropharmacological interventions. The trophic effects of cutaneous nerves on follicular growth are mediated through the regulation of vascular tone (providing oxygen, hydrogen, and nutrients), neuropeptide stimulation of the receptors of follicular keratinocytes and papillary fibroblasts, and the regulation of mast cell and macrophage activity. By contrast, follicular growth can be delayed experimentally by cutting the peripheral nerves and dorsal nerve roots.

Inhibitors of the hair cycle ■■ ■■ ■■ ■■ ■■

■■ ■■ ■■ ■■ ■■

Cortisol Oestrogens Corticotropin-releasing hormone ACTH Prolactin Epidermal growth factor (EGF-2, EGF-5) Brain-derived neurotrophic factor Neurotrophins 3 and 4 TGF-α TGF-β1, TGF-β2

Interleukins (IL-1, IL-6) ■■ ■■

Retinoids Calcitriol

The hair of domestic carnivores does not grow continuously, but follows an asynchronous cycle, so called because the growth of the hair follicle is not constant (cyclic), and because different follicles are found at different stages of growth (asynchronous). Hair is thought to grow continuously in certain dog breeds, such as poodles, bobtails, and schnauzers, although this has not been scientifically proven. The relative duration of each phase of the cycle can vary depending on age, body region, breed, and sex, and can be modified by physiological and pathological factors. The hair cycle is controlled mainly by the photoperiod and ambient temperature, although other parameters such as nutritional status, hormones, overall health, and genetic factors can also exert an influence. Follicular activity is highest in summer and lowest in winter. For example, in summer 50 % of follicles are in telogen phase. This proportion increases to 90 % in winter. Dogs and cats exposed to many hours of artificial light can shed extensively throughout the year. Sinus hairs are unaffected by seasonal shedding and grow continuously. The period of growth and the length of the hair is determined by genetic factors. Hair in each region of the body grows to a specific length. Once this length is reached, growth stops.

Hair cycle and structure of the pilosebaceous unit in carnivores

Other endogenous substances that affect the hair cycle include growth factors and cytokines produced by the follicle, the dermal papilla, and the adjacent cell population (lymphocytes, macrophages, fibroblasts, and mast cells). Given that hair consists mainly of protein, nutrition significantly influences hair quantity and quality. Poor nutritional status can result in dull, dry, thin hair. Systemic diseases shorten the anagen phase and can result in the synchronised entry of large numbers of follicles into telogen phase. Since hair in telogen phase is more easily shed, the animal may shed excessively. Systemic stress or serious illness can cause a majority of follicles to enter telogen phase in a synchronised manner (telogen effluvium), resulting in marked transient alopecia (Fig. 8). The hair cycle can also be affected by hormonal changes. In general, the anagen phase is initiated and promoted by thyroid hormones and growth hormone. However, high doses of corticosteroids and oestrogen inhibit the anagen phase and follicular growth. The cells of the dermal papilla, which constitute the mesenchymal component of the bulb,

Figure 8. Telogen effluvium in a puppy with an acute digestive condition.

play a key role in the induction of epithelial differentiation. These cells, which are derived from dermal fibroblasts, respond to hormones, and in turn emit growth signals to follicular epithelial cells. In general, the factors that control follicular structure differ to those that control the hair cycle. Changes affecting the factors that control follicular structure cause follicular dysplasia, while alterations in the levels of factors that mediate the hair cycle give rise to follicular atrophy.

HAIRCOAT COLOUR AND TYPE IN DOGS Haircoats in dogs are classified as normal, short, or long: ■■ The normal coat is exemplified by that of the German shepherd, as well as wild canids such as wolves and coyotes. It is composed of primary hairs, which form a thick coat, and finer secondary hairs. Secondary hairs account for the largest proportion of hairs by number, but not by weight. ■■ The short coat can be classified as compact or fine. The compact coat corresponds to that of Rottweilers and the majority of terriers. This type of coat has a larger number of primary hairs, and a much smaller proportion of secondary hairs. The total weight of the hair is less than that of the normal coat. The fine short coat is that seen in boxers, dachshunds, and miniature pinschers. This type of coat has the largest number of hairs per body surface area. The secondary hairs are numerous and well developed, while the primary hairs are smaller in size than those of the normal coat. ■■ The long coat in turn is subdivided into two types: fine and compact. The fine long coat is found in breeds such as the Cocker spaniel, Pomeranian, and Chow Chow. This type of coat has the greatest weight per unit of body area, except in miniature breeds, whose finer hair weighs less. The compact long coat is found in poodles, Bedlington terriers, and Kerry blue terriers. Secondary hairs account for the majority (70 %) of the coat in these breeds, which tend to shed less hair than other breeds.

DIAGNOSIS OF ALOPECIA in dogs and cats

Hairs in catagen phase are difficult to observe. The shape of catagen bulbs is between that of anagen and telogen bulbs. The tip of a healthy hair should be smooth and sharp, with a regular contour. The hair shaft should have a regular diameter, with clear demarcation of the cuticle, cortex, and medulla (Fig. 3). Pigmentation will depend on the haircoat and breed of the animal. Animals with straight hair coats have a straight shaft, while those with curly or wire hair coats have curved shafts (Fig. 4).

CHANGES IN HAIR COMPOSITION AND STRUCTURE The most common change is the appearance of split ends in animals that have pruritus or groom excessively (Figs. 5 and 6). Hair breakage due to the presence of abnormal shafts can be observed in colour dilution alopecia and other congenital diseases, trichorrhexis nodosa, axillary trichomycosis, alopecia areata, trichomalacia, and dermatophytosis.

There should be a mixture of hairs in anagen and telogen phases, although the proportion will depend on many factors, including the season and the influence of different hormones.

Longitudinal splitting of the shaft or “split ends” is known as trichoptilosis and indicates external trauma due to excessive licking, scratching, or grooming (Fig. 7). Trichoptilosis has also been described as a congenital defect in golden retrievers. This manifests as a hair shaft hyperfragility syndrome, which

Figure 3. Well formed, regularly contoured hair shaft and tip.

Figure 4. Follicular bulb from a curly-haired dog.

Figure 5. Cut and frayed hair tips in a cat caused by excessive grooming due to pruritus.

Figure 6. Cut and frayed hair tips in a cat caused by excessive grooming due to pruritus.

Diagnostic methods. Microscopic examination of hair

Twisted hair or pili torti is a rare disorder in which the shaft of the hair is flattened and twisted around itself. This disorder has been described in humans. It has a hereditary basis and may be accompanied by other cutaneous and systemic symptoms. In veterinary medicine it has been described in young cats and in bull terriers with acrodermatitis. In cases described in cats, onset usually occurs very early (10 days of age). It may occur alone or in conjunction with other symptoms, such as podal, periocular, or paronychial dermatitis.

Figure 7. Shaft showing longitudinal fragmentation or trichoptilosis.

predisposes the animal to trichoptilosis in response to even mild external trauma, such as the use of topical insecticides. Breakage of the hair in these cases does not usually occur at the base of the shaft, but near the top, resulting in an appearance that is closer to hypotrichosis than alopecia. Trichorrhexis nodosa is the appearance of small deformities in the form of nodules in the hair shaft. These deformities lack cuticle. Breakage of the hair at these nodules gives the hair shaft the appearance of two brooms pushed end to end (Fig. 8). This anomaly has been described in cats continuously treated with topical treatments for flea control.

Figure 8. Trichorrhexis nodosa.

Abyssinian cats can present a hereditary or congenital malformation that affects the tip of the hair and manifests as an onion-shaped swelling. In the case of dogs with diluted coats, melanin forms dispersed clumps of varying sizes in the cortex of the hair but does not result in breakage of the shaft (Fig. 9). If animals with diluted coats develop alopecia, these clumps can group together, creating weak points and secondary breakage of the hair shaft. Follicular casts are sheaths of keratin that cover the hair shaft (Fig. 10) and appear in both primary and secondary keratinisation disorders, such as those associated with sebaceous adenitis, demodicosis, endocrinopathies, primary seborrhoea, and follicular dysplasias.

Figure 9. Accumulation of melanin in the hair shaft cortex

in a dog with a diluted coat.

DIAGNOSIS OF ALOPECIA in dogs and cats

Figure 10. Follicular casts in a dog with sebaceous

Figure 11. Dystrophic bulbs in a dog with follicular dysplasia.

adenitis.

Abnormalities of the follicular bulb can be associated with inherited and congenital disorders as well as metabolic and nutritional diseases (Fig. 11). Animals with alopecia areata show some normal hairs in telogen phase, as well as other hairs with dystrophic bulbs and frayed, broken, and pigmented tips that taper towards the proximal end in the form of an exclamation mark (Fig. 12).

INFECTIOUS AND PARASITIC AGENTS Microscopic examination is useful for the diagnosis of demodicosis in very young or restless animals or in locations in which scrapings are difficult to obtain, such as the eyelid or interdigital space. Compared with skin scraping and exudate analysis, the trichogram is a less sensitive technique for the diagnosis of demodicosis. Sometimes this test can be negative, despite the presence of many mites. The use of mineral oil to collect the sample and visualise the parasite is recommended (Fig. 13).

Figure 13. Trichogram revealing the presence of a mite (Demodex canis).

Figure 12. Dystrophic bulbs in a dog with alopecia areata.

Diagnostic methods. Microscopic examination of hair

The hair of animals with dermatophytosis may contain arthroconidia, which group together and ensheath the cuticle of the affected hair (Fig. 14). This can cause oedema of the cortex and medulla of the hair shaft. Parasite eggs or nits can be observed in the hair shaft (Fig. 15).

SKIN BIOPSY IN ALOPECIA Skin biopsy can aid the diagnosis of alopecia in many cases. Biopsy is indicated in acute and severe cases: ■■ When alopecia is accompanied by severe general symptoms. ■■ When the clinical features are accompanied by unusual skin lesions, to confirm diagnosis before beginning treatment with a medication with side effects. ■■ When the animal does not respond to what is considered an appropriate treatment. ■■ When there are multiple differential diagnoses and diagnosis cannot be established through examination and the use of common diagnostic techniques. To obtain an accurate diagnosis an appropriate sample must be carefully selected and harvested.

Figure 14. Hair infected with Microsporum canis. The arthrospores are

distributed in chains, destroying the hair cuticle.

Before selecting the area to be biopsied it is important to examine the types of lesions present, review the differential diagnosis, and note the localisation of lesions, as skin histology varies in different parts of the body (Table 1). For example, glabrous skin has fewer hair follicles and smaller sebaceous glands, and is thus not a suitable area for the assessment of endocrine disorders. It is advisable to take multiple biopsies representative of the different types of lesions. In the case of alopecia, the sample should be taken from the centre of the most alopecic area (Figs. 16–18). Samples should also be taken from healthy tissue and from tissue bordering the lesions of interest. All samples should be stored in properly labelled containers to avoid confusion.

BOX 1 Correct biopsy protocol. Perform biopsy only in pathologies for which it is indicated. Identify all types of existing lesions. Prioritise based on primary lesions.

Figure 15. Felicola subrostratus (cat lice). Adult lice and nits.

Select the technique to be used and the appropriate number of biopsies.

DIAGNOSIS OF ALOPECIA in dogs and cats

Table 1. Causes of focal and multifocal alopecia in dogs. Causes Infectious

Focal and multifocal alopecia in dogs

Processes

Bacterial folliculitis Leishmaniasis

Parasitic

Demodicosis

Immune-mediated

Foliaceus pemphigus Alopecia areata Dermatomyositis Sebaceous adenitis

Neoplastic

Epitheliotropic lymphoma

Vascular

Drug reactions Injection site alopecia

Pruritus

Epilation Skin scraping

Dermatophytosis

Negative

Positive

Culture in DTM

Demodicosis

Negative

Alopecia induced by scratching

Positive

Traction alopecia Ischaemic skin diseases Traumatic

Burns Pruritus

If lesions are indicative of bacterial folliculitis, a two-week therapeutic trial with antibiotics may be required. Cytology may reveal acantholytic cells suggestive of pemphigus foliaceus. In the event that all the aforementioned tests are negative and the dog shows no clinical improvement with antibiotic treatment, skin biopsy is recommended (Fig. 1).

GENERALISED OR DIFFUSE NONINFLAMMATORY ALOPECIA IN DOGS Noninflammatory hair loss in dogs may be due to telogenisation of the root caused by either metabolic disorders (hormonal disease, telogen effluvium) or follicular disorders (alopecia X, post-clipping alopecia, pattern alopecia, flank alopecia). Noninflammatory alopecia can be congenital or acquired (congenital alopecia or follicular dysplasia) or caused by iatrogenic lesions of the hair matrix (e.g. following chemotherapy). In addition, causes that are initially inflammatory in nature may result in noninflammatory alopecia (scarring alopecia) (Table 2).

Presence of lesions compatible with pyoderma

Absence of lesions compatible with pyoderma

Dermatophytosis

Cytology

Not significant

Intracellular bacteria

Acantholytic cells

Antibiotic trial

Bacterial folliculitis

Possible pemphigus foliaceus Biopsy

No improvement

Improvement

Biopsy

Bacterial folliculitis

Possible diagnoses: ■■ Alopecia areata ■■ Ischaemic dermatopathies ■■ Drug reactions ■■ Epitheliotropic lymphoma ■■ Sebaceous adenitis

Figure 1. Diagnostic protocol for focal and multifocal alopecia in dogs.

Diagnostic approach based on clinical signs

In cases of possible diffuse or generalised alopecia in dogs in which the noninflammatory nature of the condition is not clear, skin scrapings or cultures in special media should be performed to rule out demodicosis or dermatophytosis. In these types of cases microscopic examination of the hair (trichogram) is important to detect the accumulation of melanin in the hair shaft or identify dysplastic bulbs (colour dilution alopecia, pattern alopecia, alopecia areata) (Fig. 2). If all these tests are negative, and the animal is of less than 5 years of age, the breed, haircoat type, distribution of alopecia, and clinical history should be considered before suspecting pattern alopecia, colour dilution alopecia, follicular dysplasia, cyclic flank alopecia, alopecia X, sebaceous adenitis, or alopecia areata. Skin biopsy may help confirm these diagnoses (Fig. 2). For animals of over 5 years of age, a medical history should be taken and a rigorous physical examination performed, as well as blood and urine analyses, diagnostic imaging (e.g. abdominal ultrasound), or

Table 2. Causes of diffuse noninflammatory alopecia in dogs. Causes

Processes

Congenital and hereditary

Ectodermal dysplasia Black hair follicular dysplasia Colour dilution follicular dysplasia

Endocrinopathies

Cushing syndrome Hypothyroidism Sex hormone imbalance

Alopecia associated with systemic causes

Telogen effluvium Anagen effluvium Paraneoplastic alopecia Malabsorption syndromes

Idiopathic

Post-clipping alopecia Cyclic flank alopecia

hormonal tests for the diagnosis of Cushing syndrome, hypothyroidism, or excess levels of oestrogens or androgens. If diagnosis cannot be established using these approaches, biopsy is indicated (Fig. 2).

FOCAL AND MULTIFOCAL ALOPECIA IN CATS Focal and multifocal alopecia in cats can be self-induced (due to pruritus or behavioural disorders), caused by inflammatory processes affecting the follicle (dermatophytosis, demodicosis, bacterial folliculitis), or caused by bulbar atrophy (corticosteroids, scarring, injection site reactions, paraneoplastic alopecia) (Table 3). In cases of focal alopecia in cats it is important to determine whether the skin has an atrophic appearance, as the cutaneous injection of drugs (e.g. glucocorticoids, vaccines, antibiotics, NSAIDs) is a common cause of this type of alopecia. If there is no history of drug administration and the skin shows no signs of atrophy, tests for the diagnosis of parasitic infections (brushing, acetate tape preparations, epilation, and skin scrapings) should be performed. If the results are negative, the hair should be analysed using a trichoscope. This is a highly useful test for the diagnosis of multifocal alopecia in cats. Fracturing of the hair shaft suggests that the alopecia has been caused by the use of aggressive topical products (e.g. insecticides); if the tips are broken, self-induced alopecia caused by pruritus or a behavioural disorder should be suspected. Intact tips and distorted bulbs are characteristic of congenital follicular dysplasias, immune-mediated diseases, and neoplastic or paraneoplastic disorders, which should be confirmed by biopsy (Fig. 3). The presence of fungal arthrospores in the hair is cause to suspect a dermatophyte infection.

Pattern alopecia Alopecia X Scarring

Secondary to leishmaniasis, dermatophytosis, demodicosis

If the aforementioned techniques fail to provide any diagnostic information, culture in dermatophyte test medium (DTM) is recommended to rule out

DIAGNOSIS OF ALOPECIA in dogs and cats

Noninflammatory alopecia in dogs

Epilation Skin scraping

Negative

Positive Demodicosis

Culture in DTM

Positive

Negative

Dermatophytosis

Trichogram

Normal ■■ ■■

■■ ■■

■■ ■■ ■■

Over 5 years of age

Less than 5 years of age

Blood and urine analyses Diagnostic tests for hyperadrenocorticism Thyroid tests Abdominal ultrasound Preputial cytology

Evaluate location of alopecia and haircoat type

Diagnosis

No diagnosis

Hyperadrenocorticism Hypothyroidism Sex hormone imbalance

Skin biopsy

Possible diagnoses: ■■ Pattern alopecia ■■ Alopecia areata ■■ Alopecia X ■■ Cyclic flank alopecia ■■ Sebaceous adenitis

Biopsy to confirm diagnosis

Figure 2. Diagnostic protocol for generalised or diffuse noninflammatory alopecia in dogs.

Melanin aggregates Dysplastic follicular bulbs

Possible diagnoses: ■■ Follicular dysplasia ■■ Pattern alopecia ■■ Colour dilution alopecia ■■ Alopecia areata

PRESENTATION BROCHURE

Ana Mª Ríos Boeta