Equine Dermatology Quiz

Equine Dermatology Engagement Session

• Dr Alissa Cooper led the session
• She has a BSc, BVetMed, PGCertVetEd, FHEA, and MRCVS qualifications
• She is a lecturer in equine clinical practice at the University of Surrey

Learning Objectives

• Discuss the presentation, diagnosis, and treatment for sarcoids in horses
• Discuss the presentation, diagnosis, and treatment for dermatitis in horses
• Discuss the presentation, diagnosis, and treatment for melanoma in horses
• Discuss the pathogenesis, diagnosis, and treatment for exuberant granulation tissue in horses

Case Study 1

• A 12-year-old Haflinger gelding presented with a skin lesion on its right caudal abdomen
• The lesion had been present for two years, showing slow and gradual growth
• The lesion's diameter increased gradually, and recently developed more thickening in the center
• Questions to ask the owner include whether the lesion is itchy, location of additional lesions, if other horses are affected, previous treatments, known causes, recent changes, and general health/preventative health
• The lesion is well-circumscribed, alopecic, and has epidermal thickening, hyperkeratosis, verrucous change centrally, pigment change, and lichenification
• Differential diagnoses include sarcoid (occult/verrucous-mixed), dermatophytosis, scar, chronic skin irritation/rubbing, and autoimmune disease
• Diagnostics to consider are skin scrape/hair pluck to rule out other differentials, skin biopsy (incisional or excisional), and awareness of potential risks of making the condition worse
• A treatment plan must be developed
• Treatment options for sarcoid include topical therapy (AW5 cream, imiquimod, 5-fluorouracil), surgery (ligation/banding, laser surgery, sharp resection), chemotherapy/electrochemotherapy, radiotherapy, cryotherapy, immune modulation, photodynamic therapy, and benign neglect
• Periocular sarcoids may require topical/surgical treatment, with skin expanders potentially necessary for reconstruction of the lid
• Intralesional therapy using BCG can be effective but can be difficult to acquire
• Radiation is also possible
• Owners should be warned that treatment may be a long and difficult process, with some cases showing surprising success. Invasive fibroblastic lesions on the muzzle may be targeted with cryotherapy and intralesional 5FU
• Note that surgical removal is usually the best treatment if lesions are still small

Case Study 2

• A 10-year-old Welsh pony mare presented with intense pruritus during the summer, increasingly severe over three seasons
• The pony scratches its rump, tail, and mane, resulting in self-induced alopecia and excoriations
• Similar lesions are noted on the mane
• Questions to ask the owner include how long they've owned the horse, its current management (stabled/turned out), turnout conditions, rug use, topical shampoos, diet, parasite control history, and previous treatments
• Differential diagnoses include Culicoides hypersensitivity (sweet itch), dermatophilosis (rain scald), dermatophytosis (ringworm), contact hypersensitivity, hypersensitivity to other flies/insects, and louse infestation
• Diagnostics include clinical presentation evaluation, environment evaluation (stagnant water for midge breeding), hair plucks, skin scrapes, scurf examination, rule out of ectoparasites, intradermal skin test, checks for/rule out other allergens, and a biopsy
• Management involves management changes to control or reduce exposure to the inciting cause (fly rugs/masks, fly repellent), moving field during summer, stabling during dawn and dusk, fans in stable, starting control measures before midge season, and other options such as SSS/lotions/baths
• Treatment may include medications to reduce pruritus severity like anti-inflammatories (prednisolone/dexamethasone), avoiding long-term steroid use, and considering laminitis risk. Antihistamines also may be helpful
• Desensitization therapy and nutritional supplements may also be considered

Case Study 3

• A 6-year-old cob gelding presented with pruritus to distal limbs
• The signs developed after a move to new yards in September
• The horse stamps its feet, rubs its legs, and bites its pasterns
• No previous history of skin conditions
• Questions to ask the owner include details about the timing, symptoms progression, history of skin conditions/past treatments, and other animals/environment that may be in contact with the horse
• Lesions are described as diffuse, alopecic, erythematous, with scurfy scales and exudate, skin thickening, and pruritic.
• Diagnostic approach involves a skin scrape, sticky tape impression, hair plucks for fungal rule out, and biopsy.
• Preliminary diagnosis includes chorioptic mange (Chorioptes bovis), skin dwelling/scurf feeding mite, and more prevalent in house horses; consideration that the outbreak can be caused by shared equipment
• Management advice includes clipping hair, removing bedding, cleaning and disinfecting the stable daily, treating contact animals, a pig oil/white mineral oil and yellow sulfur patch test, and stopping sharing equipment.
• Treatment includes thorough cleaning with appropriate shampoo (keratolytic or selenium sulfide). Historically, Doramectin (Dectomax injection) may be given, and topical treatments such as Fipronil spray (effective if clipped) and Ivermectin/moxidectin
• Further management may also involve lime sulfur spray, repeated every 7-14 days

Case Study 4

• A 12-year-old grey Connemara mare presented with several nodular masses in the perineal region, gradually increasing in size over 6-8 months.
• Clinical examination revealed additional nodules in the right groin region and a swelling in the left parotid region.
• Differential diagnoses include melanomas, sarcoids, and mast cell tumors
• Diagnostics involve fine needle aspiration (FNA) to identify pleomorphic and atypical melanocytes, and biopsy to confirm atypical melanocytes
• Melanoma treatment options include surgical removal (easier when lesions are small), diode laser, chemo/electrochemotherapy, cryosurgery, Oncept vaccine + Tyrosinase inhibitor, and autologous vaccine. Cimetidine treatment can be given for possible treatment. It is important to not neglect it as melanomas should not be underestimated
• Benign neglect should not be a treatment option and should be avoided because they can lead to malignant issues.