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Equine Pastern Dermatitis: Scratches, Grease Heel, Dew Poisoning, & Mud Fever
Pastern Dermatitis:
Scratches, Grease Heel, Dew Poisoning, Mud Fever, and Photosenstization in Horses
Introduction
No matter what you call it: scratches, grease heel, dew poisoning, or mud fever, this condition with many causes may all look very similar. Often painful and occasionally pruritic (itchy) this condition is characterized by hair loss, irritated skin, and in time crusts (scabs) and open sores that forms on the heels and pastern. Unchecked this condition may spread to the coronet band and further up the leg. Lameness may be present. This report concerns itself with the differentiating the causes, treatment, and prevention of these conditions.
Causes and Clinical Signs
The problem is first noted as hair loss, sores often with thick scabbing on the pasterns and over the heels and is often painful and sometimes accompanied by swelling and heat. When severe the horse will be lame. The problem can be just one or all of the feet and legs and usually will progress up the leg or spread to other legs. The breed of the horse, color of the affected skin and hair, environmental conditions, number of legs affected, whether they are itchy (pruritic), and distribution of the lesions may help with determining a cause.
Staph Dermatitis (Primary): Scratches
Most commonly scabbing, sores, swelling is due to a primary infection often due to chronic wetting and mechanical irritation to the skin and often referred to as "Scratches". The wetting and irritation allows for a bacterial infection often staphylococcus but some times dermatophilus and rarely a yeast infection (Malassezia). However some cases of scratches may not be a secondary to other causes and the primary cause needs to be identified and corrected for resolution.
Sunburn / Photosensitization / Leukocytoclastic Vasculitis
Whenever the pastern dermatitis is confined to the white haired areas of the skin consideration for the diseases that cause photosensitivity should be undertaken though it does not rule out simple pastern dermatitis. Photosensitization can be broken down to several different primary causes:
- Simple sunburn, usually just the dorsal upward facing aspects of the skin and includes the white parts of the head and upper body.
- Ingestion of plants or drugs that contain photodynamic chemicals like tetracycline.
- Liver disease, often secondary to ingestion of hepatotoxic plants...more
- Occasionally on biopsy a primary vasculitis is found and has been labeled pastern leukocytoclastic vasculitis. Pastern leukocytoclastic vasculitis appears to be an immune mediated photo-hypersensitivity that effects the white portions of the lower legs. Interestingly not all white legs may be effected suggesting a local cause. Some hypothesize chronic injury to the skin has allowed bacteria to creep in under the skin and activated the immune system.
Mange Mites (Chorioptes, Psoraptes, Sarcoptes)
If the pastern dermatitis is accompanied by intense rubbing and bitting at the area, usually associated with pruritus, particularly in horses with feathers consider the pastern mange mites: chorioptes (usually draft horses), psoraptes, or sarcoptes mange mites...more.
Chronic Progressive Lymphoedema (Lymphedema)
In the cold blood or draft lines of horses consideration of Chronic Progressive Lymphoedema (Lymphedema) should be given. The condition is characterized by a progressive swelling, thickening of the skin (hyperkeratosis), and formation of large nodules (fibrosis) often referred to as "grapes" on the lower portions of the limbs in Shire, Clydesdale, and Belgian draft horses. With time secondary infections and ulceration occur. The disease starts at an early age, progresses throughout the life of the horse, ...more.
Coronitis
If just the coronary band is affected consider the diseases that cause coronitis...more.
Diagnosis
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