Lumps, Bumps

and Scratches

A guide to

common equine

skin diseases

• 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

Overview of Lecture

Skin – what a marvelous

organ!

• 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

Quiz

Ringworm Hives

Quiz continued

Pastern

dermatitis/Scratches Squamous cell carcinoma

Dermatology terms

• 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

The Itchy Horse

Symptoms: • Change in

behavior

• Hair loss +/-

excoriations

• Hives or other

lesions

Causes: • Ectoparasites

• Allergies

• Bacterial/

Fungal

infections

Parasites – mites

Chorioptic mange:

• (leg and tail) – breeds with

feathered fetlocks

• Symptoms – itching, stamping

feet, biting legs, crusts

• Diagnosis – skin scrapings to

examine under microscope

• Treatment: Lime sulfur rinses,

fipronil (Frontline) spray,

ivermectin can help but not

curative

Psoroptic Mange (body or ear

mange):

• Symptoms – evidence of itching, esp

near mane and tail

• Diagnosis same as Chorioptes

• Treament – ivermectin works well.

Lice – sucking and biting

• 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

Allergies

• Atopic dermatitis

(hypersensitivity to

environmental or food

allergens)

• Culicoides

hypersensitivity (Sweet

Itch)

• Other insect

hypersensitivities

Atopic dermatitis

• 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.

Diagnostics

• 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

Treatment Options

• Allergen specific immunotherapy (allergy shots)

• 2-3 months to see improvement

• 60-80% of horses improve

• Injections for life (once monthly for maintenance)

• Symptomatic treatments:

• Topical sprays

• Corticosteroids

• Antihistamines

• Omega fatty acids

• Skin supplements

• No cure –

lifetime of

treatment

Sweet Itch

• 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

Management

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…

Pemphigus Foliaceus

• 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

• Diagnosis:

• Rule out other causes such as bacteria or dermatophytes

• Biopsy

• Treatment:

• Corticosteroids (Prednisolone/Dexamethasone)

• Avoid sunlight

• Shampoo to control pruritis

• 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

Photodermatitis

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

plants increase levels of

phylloerythrin in skin ex: ragwort,

rape, kale

• Light skinned, sparsely haired areas

• Diagnosis: Hx, PE, investigate

pasture, labwork to assess liver

disease

• Treatment: ID and eliminate

cause

• Avoid UVL

• Symptomatic treatment

for skin

Ringworm/Girth Itch

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

Rarely transmitted to humans

Fungal infections

Fungal diagnosis &

management

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

Bacterial infections

• Often the result of skin trauma

secondary to other disease

processes

Rainrot - Dermatophilus congolensis

• 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

Pastern Dermatitis

“scratches/mud fever”

• Caused by same

bacteria that causes

Rainrot!

• Chronic problem

• Can be difficult to

treat/cure

• White legs prone

• Can develop into

cellulitis (systemic

antibiotics)

Neoplasia (skin masses)

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)

Sarcoids

• 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

Squamous cell carcinoma

• 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

SCC

Melanomas

• 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.

Cutaneous Lymphoma

• 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?

Take home message:

• 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.

Any Questions?