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EQUINE DERMATOLOGY ISBN 0-7216-2571-1

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E quine skin disorders are common and important. After dogs and cats, horses are the most common species presented to our Dermatology Service and telephone consultation service for evaluation. In general, the equine dermatoses seen worldwide are similar both in nature and frequency. 1-8 Very little information is available concerning the demographics of equine skin disorders. A survey carried out by the British Equine Veterinary Association in 1962 and 1963 indicated that

2% of all cases seen by the membership were presented for skin disease.

9

A 1989 survey of the

members of the American Association of Equine Practitioners revealed that skin disorders were the fourth most common medical problem encountered (following colic, viral respiratory tract disease, and endometritis). 10 The top 10 equine health problems as determined by a survey of horse owners included skin diseases, which ranked number 9. 11 Panel reports of veterinary practitioners in 1975, 1981, and 1986 found that dermatophytosis, dermatophilosis, urticaria, insect hypersensitivities, onchocerciasis, eosinophilic granulomas ("nodular necrobiosis"), papillomas ("warts"), sarcoids, photodermatitis, and nutritional "seborrheas" were the most commonly encountered equine skin disorders. 4-6

In a 21-year (1979-

2000) retrospective study of equine skin disorders at the College of Veterinary Medicine at Cornell

University, 4.1% of all horses examined at the Large Animal Clinic were evaluated by a dermatologist for skin problems (Tables 1 and 2). 12

There was no breed predisposition for skin

Preface and Acknowledgments

v Table 1COMMON HORSE BREEDS PRESENTED FOR DERMATOLOGIC

DIAGNOSIS

12

PERCENTAGE OFPERCENTAGE OF TOTAL

BREEDDERMATOLOGY CASESHOSPITAL POPULATION

Thoroughbred23.922.9

Quarter Horse16.514.6

Standardbred15.824.2

Arabian6.45.2

Appaloosa5.85.4

Morgan4.53.0

Belgian3.92.1

American Paint1.81.8

Percheron1.10.7

American Saddle Horse 0.90.6

Clydesdale0.60.4

All other breeds18.819.1

W2571-FM.qxd 2/1/03 11:46 AM Page v

vi•Preface and Acknowledgments Table 2DERMATOLOGIC DIAGNOSES* FOR 900 HORSES OVER A 21- YEAR

PERIOD (1979-2000)

12

DIAGNOSIS# OF CASES % OF CASES

Bacterial folliculitis10611.78

Dermatophytosis808.89

Insect hypersensitivity576.33

Dermatophilosis505.56

Drug reaction374.11

Eosinophilic granuloma353.89

Atopy353.89

Vasculitis303.33

Chorioptic mange242.67

Equine sarcoid232.56

Urticaria, idiopathic222.44

Idiopathic pruritus192.11

Pemphigus foliaceus171.89

Erythema multiforme171.89

Onchocerciasis151.67

Ear papillomas131.44

Viral papillomatosis121.33

Alopecia areata121.33

Follicular dysplasia121.33

Pediculosis111.22

Idiopathic seborrhea111.22

Unilateral papular dermatosis111.22

Dermoid cysts101.11

Bacterial pseudomycetoma101.11

Telogen defluxion101.11

Melanoma91.00

Lymphoma91.00

Anagen defluxion91.00

Habronemiasis91.00

Coronary band dysplasia91.00

Ventral midline dermatitis80.89

Cannon keratosis70.78

Contact dermatitis 70.78

Verrucous hemangioma60.67

Linear keratosis60.67

Trichorrhexis nodosa60.67

Vitiligo60.67

Bacterial cellulitis60.67

Traumatic alopecia50.56

Blackfly bites, pinna50.56

Sterile eosinophilic folliculitis50.56

Secondary seborrhea, hepatic50.56

Pseudolymphoma50.56

Epidermal nevus50.56

Schwannoma50.56

Sterile pyogranuloma40.44

Sterile panniculitis40.44

Sarcoidosis40.44

Tick bite granuloma40.44

Hyperadrenocorticism40.44

Food hypersensitivity40.44

Behavioral self-mutilation40.44

W2571-FM.qxd 2/1/03 11:46 AM Page vi

disease as a whole. Due to the referral nature of our practice, the types and frequencies of the various dermatoses documented would not be expected to be those seen in general equine practice. The "Top 10" equine dermatoses seen at our clinic were bacterial folliculitis, dermato- phytosis, insect hypersensitivity, dermatophilosis, drug reaction, eosinophilic granuloma, atopy, vasculitis, chorioptic mange, and equine sarcoid. In a 16-year (1978-1994) retrospective study of biopsy specimens submitted to the Diagnostic Laboratory, College of Veterinary Medicine, at Cornell University, 23.4% of all equine submissions were skin lesions. 12 Interest in equine dermatology has resulted in its being reviewed in a number of textbooks 13- 36,46
and continuing education articles. 37-44
Of particular note is the special issue of Veterinary Dermatology dedicated to the late Dr. Tony Stannard. 45

Skin diseases are a source of animal

suffering - through annoyance, irritability, pruritus, disfigurement, secondary infections, myiasis, and increased susceptibility to other diseases. In addition to compromising the animal's comfort

Preface and Acknowledgments•vii

Table 2DERMATOLOGIC DIAGNOSES* FOR 900 HORSES OVER A 21- YEAR

PERIOD (1979-2000)

12

ÑcontÕd

DIAGNOSIS# OF CASES % OF CASES

Mane and tail seborrhea30.33

Idiopathic pastern dermatitis30.33

Discoid lupus erythematosus30.33

Epitrichial sweat gland neoplasm30.33

Spotted leukotrichia30.33

Amyloidosis30.33

Barbering30.33

Burns20.22

Bullous pemphigoid20.22

Lymphangitis, bacterial20.22

Photodermatitis, hepatic20.22

Systemic lupus erythematosus20.22

Epitheliotropic lymphoma20.22

Squamous cell carcinoma20.22

Idiopathic delayed shedding20.22

Sporotrichosis20.22

Eumycotic mycetoma20.22

Photic headshaking20.22

Pressure sores20.22

Multisystemic eosinophilic epitheliotropic disease 20.22

Aplasia cutis congenita10.11

Malignant fibrous histiocytoma10.11

Carcinosarcoma10.11

Halicephalobiasis10.11

Phaeohyphomycosis10.11

Cutaneous asthenia10.11

Mast cell tumor10.11

Arsenic toxicosis10.11

Hypotrichosis10.11

Trichoepithelioma10.11

Pili torti10.11

Strawmite dermatitis10.11

Organoid nevus10.11

Lichenoid keratosis10.11

*Where more than one dermatosis was present at the same time in one horse, only the most important are listed.