Exam #3: Equine Derm Flashcards
Six main categories of equine derm problems
1) Pruritus
2) Crusting and scaling
3) Ulcers and erosions
4) Lumps and bumps
5) Discoloration
6) Hair coat changes
Main diagnostics tests for equine derm conditions (8)
- Similar to small animal derm
1) Skin scrape
2) Combings of mane, tail, feathers (ectoparasites)
3) Scotch tape preps (cytology)
4) Trichograms
5) Dermatophyte culture- monitor freq so it’s not overgrown by normal bacteria of saprophytic fungi
6) Impression smear or crust cytology
7) Culture for bacterial or fungus
8) Skin biopsy - Suspect systemic dz? run CBC, chem, diet elimination trials, intradermal testing
Top four differentials for pruritus in horses
1) Ectoparasites
2) Insect hypersensitivity
3) Allergic hypersensitivity
4) Urticaria
DDx? Pruritus of lower legs, tail, foot, (may become generalized), “scratches”, alopecia, crust formation
> Mites
- Most commonly in horses is Chorioptes (legs, tail, foot)
- Psoroptes (droopy ears, mane, trunk involvement)
Treatment of choice for mites
Ivermectin, others = 5% lime sulfur
Dx? Intense pruritus, beginning on the head, non-follicular papules, crusts, excoriations, alopecia
Mites = Sarcoptes
- Cross-species transmission possible
- Reportable and zoonotic
What time of year are parasitic skin pathologies more common?
Winter = often more severe then
Dx? Pruritus, restlessness, poor hair coat quality, alopecia, excessive grooming of mane, head, tail, fetlocks (affected animals may be asymptomatic and just “twitchy”)
> Lice (pediculosis)
- Common in young or old/debilitated animals
- Overcrowding predisposes
- Common in colder months
Common anatomic locations of biting and sucking lice
- Biting louse (Damalina) = dorsolateral trunk, mobile
- Sucking louse (Haematopinus) = mane, tail, fetlock, stationary
Difference in location on horse between Chorioptes and Psoroptes
1) Chorioptes = leg, tail, foot
2) Psoroptes = ears, mane, tail
Treatment of lice
- Treat all animals in contact = ivermectin
- Clean environment
Dx? Pruritus, papules, wheals on muzzle and distal limbs
Chiggers (common in late summer/fall)
Dx? Anal pruritus, tail rubbing and alopecia
Pinworms - Oxyuris equi
DDX: tail pyoderma, insect bite hypersensitivity, atopic dermatitis, food allergy, chorioptic/psoroptic mange
True or false - pinworms are species specific?
True
Dx? Pruritus, painful papules and wheals with a central crust
> Biting flies
- Tabanids = horse flies = ventrum, legs, neck, withers (individual strikes/bites)
- Stomoxys = stable flies = neck, back, groin, chest, legs
Dx? Ventral midline dermatitis
Horn fly bites
What is the most common allergic skin disease in horses?
Insect bite hypersensitivity
Dx? Pruritus (location varies, common face, mane, tail, ventrum, dorsum), papules, wheals, crusts, secondary alopecia, self trauma (etc.)
Hypersensitivity to Culicoides fly saliva
Treatment of insect bite hypersensitivity
1) Limit insect exposure
2) Environmental control
3) Anti-histamines
4) Topical and systemic steroids
+/- Immunotherapy (conflicting evidence)
Dx? Chronic urticaria, generalized pruritus, secondary excoriations, lichenification, alopecia
Atopic dermatitis to environmental antigens
Diagnosis and treatment of atopic dermatitis
- Dx: exclusion
- Tx: symptomatic (corticosteroids, anti-histamines), immunotherapy
Which is more common with pruritus in horses: food allergy or contact reactions?
- More common = contact reactions, Ex: tack, saddle, irritants.
- Rare = food allergy
How do we view urticaria in horses?
> REACTION PATTERNS from different etiologies or pathogeneses (angioedema)
+ Wheal (flat topped with steep walled sides)
*Should “pit” with pressure
DDx for urticaria (6)
1) Hypersensitivity reactions
2) Drug rxns
3) Physical = cold temp, exercise induced, dermatographism
4) Stress
5) Vasculitis
6) Arthropods
Three MAIN differentials for crusting and scaling?
1) Dermatophytes
2) Dermatophilosis
3) Bacterial folliculitis due to Staph
Dx? Papules, crusts, areas of alopecia (with or w/o crusts), scaling, common to start in axillary and girth region, variable prutitus
Dermatophytes - commonly Trichophyton
DDx: dermatophilosis, bacterial pyoderma, demodicosis, pemphigus folliaceus
Dx and tx of ringworm
- Dx: DTM culture, trichogram, skin biopsy
- Tx: environmental and tack decontamination, topical lime sulfur, chlorhex/azole antifungal shampoo
Dx? “Paintbrush lesions” with yellow exudate, ulcerated skin, pain, railroad track cocci on cytology
Dermatophilosis (Dermatophilus congolensis)
Predisposing factors = moisture, skin damage, chronic carrier animals
Tx of dermatophilosis
- Dry the horse
- Remove crusts (remove from environment)
- Topical antibiotics (systemic in severe cases)
Dx? Crusts, epidermal collarettes, papules, +/- pruritus, alopecia - common near the saddle, pastern (“scratches”) and tail
Bacterial folliculitis (pyoderma) from coag + Staph
DDx: Dermatophilosis, dermatophytosis, insect bite hypersensitivity, atopic dermatitis, ectoparasites
Dx and tx of bacterial folliculitis (pyoderma)
- Dx: cytology by tape prep or glass side impression
- Tx: systemic antibiotics, possibly topical with localized lesions
Dx? Scaling dermatitis with variable pruritus (common intermammary)
Malassezia yeast
Tx: topical antifungal shampoos
Causes of dermatologic ulcers and erosions
Progression of other “lesser” signs = pruritus, crusting/scaling
Ex: secondary to self-induced excoriations from pruritus (Ex: hypersensitivity), from underneath crusts
Cause of perineal ulceration
Fecal or urine scaling from poor management
Tx: wash with warm/chlorhex water, cover with antibacterial ointment
DDx for mucocutaneous ulcerations (5)
1) Trauma
2) Drug reactions
3) Infectious = vesicular stomatitis
4) Immune-mediated - bullous pemphigus
5) Congenital - epidermolysis bullosa
What is HERDA?
Hereditary equine regional dermal asthenia - hyperextensible fragile skin due to collagen abnormality, lesions in areas of friction or trauma
DDx for lumps and bumps (6)
1) Sarcoids
2) Papillomatosis
3) Eosinophilic granulomas
4) Abscesses
5) Habronemiasis
6) Skin tumors (melanoma, SCC)
Dx and cause: wart in an adult animal
Sarcoid until proven otherwise (due to bovine papillomavirus type I and II)
- Most common equine skin tumor
- Types: occult, nodular, malevolent, verrucous, fibroblastic, mixed
Dx and tx of equine sarcoids
- Dx: biopsy (may stimulate growth afterwards)
- Tx: immunomodulating meds, cryotherapy. surgical excision, imoquimod
Dx and cause: wart-like cauliflower lesions on muzzle and distal limbs of young animals, often aural
Equine papillomatosis
Dx and tx of equine papillomatosis
- Dx: biopsy
- Tx: most spontaneously regress, speed it up with surgical excision or cryotherapy (aural masses rarely regress)
Most common non-neoplastic nodular skin disease
Eosinophilic granuloma
Dx? Single or multiple, well-circumscribed, haired, non-traumatized dermal nodules, non-painful, non-pruritic
Eosinophilic granuloma - may be associated with underlying hypersensitivity disorders
Common etiologic agent with pectoral region abscesses
Corynebacterium pseudotuberculosis = pigeon fever
Etiologic agents with abscesses (3)
1) Corynebacterium pseudotuberculosis (via fly vectors)
2) Sporothrix schenkii
3) Pythium insidiosum (swamp cancer)
Dx? Lesions/nodules on legs, ventral prepuce, urethral penile process, medial ocular canthus, chronic granulomatous inflammation, ulceration, exuberant granulation tissue
Habronemiasis - hypersensitivity to Habronema larvae in wounds or skin
DDx: infectious granulomas, eosinophilic granuloma, neoplasia, exuberant granulation tissue
Dx and tx of habronemiasis
- Dx: biopsy
- Tx: local and systemic ivermectin, debulk large lesions, systemic glucocorticoids
Dx? Tx? mass on eyelid or external genitalia, commonly in light colored horses
Squamous cell carcinoma
Tx: wide surgical excision, some chemo options
Dx? Tx? masses on the undersurface of the tail and perianal region, common in grey horses
Melanoma
Tx: wide surgical excision, radio/chemotherapy
DDx for coat discoloration (5)
1) Photosensitization
2) Leukotrichia, leukoderma
3) Hyperpigmentation
4) Effluvia, defluxion
5) Retained hair coat
Dx? Most common cause of hairless, white, or lightly pigmented areas of skin
Photosensitization
Two main types of photosensitization in the horse
1) Primary - ingestion of metabolically derived photodynamic agents that reach the skin
2) Hepatogenous = liver function can’t detoxify
Dx and tx of photosensitization
- Dx: history, PE, liver function test
- Tx: eliminate offending agent, limit sun exposure, symptomatic tx of hepatic disease, +/- antibiotics
Causes of leukotrichia or leukoderma
> Depigmentation of hair
- Breed-related = thoroughbreds, Arabians
- Drug/vax associated
- From painful crusts
- LEUKODERMA = from trauma/damage to the skin
Cause of vitiligo
Inherited condition, common in Arabs
Four main differentials for alopecia
1) Pruritus
2) Systemic illness = anagen/telogen defluxion
3) Light exposure
4) Nutritional status
Cause of retained hair coats (2)
- Poor health and management
- Underlying systemic disease (PPID)
