Lumps, Bumps and Scratches

A guide to common equine skin diseases Overview of Lecture • Skin structure and function • Why is my horse itchy? • Ectoparasites: Mites (chorioptic/sarcoptic mange) Lice • Autoimmune/Allergic: Allergies Sweet Itch Pemphigus • Photodermatitis • Fungal disease • Bacterial disease • Neoplasia/tumors • Barrier to water loss and protection from environment • Allows motion and provides shape • Produces glands, hair, hoof, secretions • Storage • Temperature regulation • Pigmentation • Immuno- surveillance/antimicrobial • Sensory perception • Indicator of general health Skin – what a marvelous organ! Ringworm Hives

Quiz Pastern dermatitis/Scratches Squamous cell carcinoma

Quiz continued • Alopecia – hair loss • Pruritus - itchy • Crusting – exudate stuck to skin, scabs • Scaling – accumulation of loose fragments of the skin • Wheals – raised edematous transient lesions, hair stands up

Dermatology terms Symptoms: • Change in behavior • Hair loss +/- excoriations • Hives or other lesions Causes: • Ectoparasites • Allergies • Bacterial/ Fungal The Itchy Horse infections

Chorioptic mange: • (leg and tail) – breeds with feathered fetlocks • Symptoms – itching, stamping feet, biting legs, crusts • Diagnosis – skin scrapings to Psoroptic Mange (body or ear examine under microscope mange): • Treatment: Lime sulfur rinses, • Symptoms – evidence of itching, esp fipronil (Frontline) spray, near mane and tail ivermectin can help but not • Diagnosis same as Chorioptes curative • Treament – ivermectin works well. Parasites – mites • Mites and lice more common during cold weather, when there has been crowding, prolonged stabling and suboptimal nutrition.

• Lice can be seen in the haircoat, mild- moderate pruritis, alopecia and scaling • Treament – 1% selenium sulfide shampoos, insecticide sprays and powders. Ivermectin effective against sucking lice

Lice – sucking and biting • Atopic dermatitis (hypersensitivity to environmental or food allergens) • Culicoides hypersensitivity (Sweet Itch) • Other insect hypersensitivities

Allergies • TB’s and Arabs – higher incidence • Multifactorial, genetic • Can be seasonal or non-seasonal • No sex predilection • Younger horses

Primary Symptoms: • Pruritis • Urticaria (hives) Secondary Symptoms: • Coat color changes (distorted melanocytes) • Self trauma, excoriations lead to alopecia

• Lots of things cause these symptoms so often diagnosed after ruling out other causes. Atopic dermatitis • Intradermal Skin Testing • Gold standard • Performed by a dermatologist (TUSVM) • Allergens used specific for NE region • Does not check for food allergies (dietary trial)

• Blood test • Getting better but still inaccurate Diagnostics • Allergen specific immunotherapy (allergy shots) • 2-3 months to see improvement • No cure – • 60-80% of horses improve lifetime of • Injections for life (once monthly treatment for maintenance) • Symptomatic treatments: • Topical sprays • Corticosteroids • Antihistamines • Omega fatty acids • Skin supplements Treatment Options • Insect hypersensitivity • Culicoides (midges, gnats, no-see- ums) • Spring through late Fall • Gets worse each year

• Two main patterns • Mane and tail • Ventral midline (belly) • VERY itchy • Excoriation, alopecia, crusting, lichenification • Secondary bacterial infections • Weight loss/anxiety Sweet Itch Insect Control: • Stable during peak times (dawn and dusk) • Flysprays, feed through insecticides • Eliminate larva • Manure pile, fly predators, water sources • Box fans, mesh screens, ceiling fans • Special fly sheets

Other treatment options: • Corticosteroids (Prednisolone/Dexamethasone) • Immunotherapy (allergy shots) can help • Dermoscent Essential 6 (“spot on” FA’s, vit E) • Treat secondary bacterial infections • Plethora of remedies…

Management • Most common autoimmune disease in horses (though still relatively rare) • Antibodies attack the intracellular cement causing separation of epidermal cells • No breed, age, or sex predilection • May follow a triggering event such as drug administration, illness, or severe stress • Reported in horses with longstanding sweet itch Pemphigus Foliaceus • Clinical signs include: • Severe crusting, scaling and alopecia, usually on the head and legs but can become generalized within 1-3 months • 50% have limb and ventral abdomen edema • 50% have systemic signs such as depression, lethargy, fever, wt loss

• Diagnosis: • Rule out other causes such as bacteria or dermatophytes • Biopsy • Treatment: • Corticosteroids (Prednisolone/Dexamethasone) • Avoid sunlight • Shampoo to control pruritis

Pemphigus 1. Phototoxicity – classic sunburn

2. Photosensitivity – increased susceptibility to UV radiation • Ingestion/production/contact with photodynamic agents • Primary - Plants: ex. St Johns Wort, rye grass • Hepatic – liver disease or hepatotoxic • Diagnosis: Hx, PE, investigate plants increase levels of pasture, labwork to assess liver phylloerythrin in skin ex: ragwort, disease rape, kale • Treatment: ID and eliminate • Light skinned, sparsely haired areas cause • Avoid UVL • Symptomatic treatment Photodermatitis for skin Dermatophytosis (fungal) • Fall/winter • Young horses • Very contagious – direct contact or fomites • Hair can be contagious for months to years!

• Face, neck, girth, classic ring lesions • Not usually pruritic • Tufted papules→scaling, crust → alopecia

Ringworm/Girth Itch

Rarely transmitted to humans Fungal infections Diagnosis: • Fungal culture on hair plucks • Biopsy

Treatment: • Ringworm infections are self-limiting but can take weeks to months • Topical therapy: • 2% Lime sulfur, Enilconazole (Canada), Malaseb shampoo or plegetts • Daily treatment for 5-7 days then 2x/week until resolved • Systemic treatment with antifungals is rarely necessary

Control: • Disinfect tack ,brushes, etc with bleach diluted 1:10

Fungal diagnosis & management • Often the result of skin trauma secondary to other disease processes Bacterial infections • Gram + bacteria, likes moisture

Symptoms: • Painful crusts • Paintbrush lesions, hair pulls off easily

Diagnosis: • Impression smear – looks like train tracks under microscope • Culture

Treatment: • Dry weather, dry horse • Bathe with iodine, chlorhex, lyme sulfur, vetericyn • Severe cases may need systemic antibiotics • No immunity so get recurrent cases Rainrot - Dermatophilus congolensis • Caused by same bacteria that causes Rainrot! • Chronic problem • Can be difficult to treat/cure • White legs prone • Can develop into cellulitis (systemic antibiotics) Pastern Dermatitis “scratches/mud fever” In horses skin is the most common site of neoplasia (50%) and most of these are benign

Most common tumors: • Sarcoids • Melanoma • Squamous cell carcinoma (eyelid and external genitalia)

* Biopsy is the key to diagnosis Treatment options – often multimodal (combination) • Surgery to remove or debulk tumor • Intralesional chemotherapy • Cryotherapy/hyperthermia • Laser therapy • Radiation therapy • Topical biologics ie Aldara • Systemic chemo (rare cases) Neoplasia (skin masses) • Common, locally aggressive, do not metastasize • Not usually life threatening but can affect use of the horse due to location • Etiology thought to be viral, can occur in areas of trauma, wounds • Head, neck, legs and ventrum • Categories: 1. Verrucous (wart-like) 2. Fibroblastic (proudflesh-like) 3. Mixed 4. Occult/flat Sarcoids • Typically locally invasive, slow to metastasize • Increased prevalence in light colored draft breeds, Appaloosas, Paints and Pintos, geldings more often affected. • Most common tumor of eyelid and external genitalia • May look like proudflesh at first • Often painful and may have foul odor

Squamous cell carcinoma SCC • Grey horses (although dark horses can get them and they are more likely to be malignant), no sex predilection • Estimated that 80% over 15yrs • Around the eye, under the tail and parotid glands • Usually firm/nodular • Some have a tarry discharge • Cause unknown but thought to be related to abnormal melanin metabolism

Melanomas • Three recognized growth patterns: 1) Slow for years without metastasis 2) Slow for years with sudden rapid growth and metastasis 3) Rapid growth and malignancy from the onset

• Many horses have metastatic disease on necropsy but most have no clinical signs related to it

Treatment options similar for other tumors • Cimetidine – antihistamine with immunomodulatory effects – may help slow the progression of the disease.

Melanomas • No breed, age or sex predilection • Many horses have concurrent systemic illness but some can have lesions for months to years before they are sick • Subcutaneous lesions are multiple and widespread • Usually firm nodules involving head, neck, trunk and upper part of limbs

Diagnosis – biopsy nodules Treatment – Prednisolone, chemotherapy?

Cutaneous Lymphoma • Many skin disorders/infections looks similar • Accurate history from the owner can be very helpful • It is often difficult to diagnose them based on appearance alone • Further diagnostics are often warranted. Take home message:

Any Questions?