Pastern Dermatitis

Pastern Dermatitis, aka “Scratches”, “Mud fever,” “Greasy heel”

Pastern dermatitis is the name for a skin reaction that can have a variety of causes. Most commonly the area affected is the back of the pasterns and heels but sometimes the inflammation can extend up the entire lower limb. White-haired areas seems to be more commonly affected than dark-haired areas. The appearance is of scabby oozing lesions on the skin, sometimes forming thick crusts. The skin when cleaned off has the bright pink appearance of inflammation and sometimes has ulcerated areas. In chronic cases the skin can become thickened and plaque-like.  This condition is very painful for the horse, and can cause lameness in some cases.

Causes for pastern dermatitis include bacterial infection, contact with caustic substances, fungal infection, mites and photosensitization related to pasture plant toxicity. Chronically wet skin and hair from environmental moisture (such as tall wet grass in a pasture) can weaken the skin’s defenses and lead to the infection that causes scratches. Some horses can have an immune-mediated condition that causes pastern dermatitis.

Treatment for pastern dermatitis includes the following:

• Clipping the hair from the affected area to allow easy access to the skin and to help keep the area dry.
• Gently cleaning the skin with warm water and antibacterial scrubs such as Betadine or Chlorhexadine. After softening the scabs and crusts with the wash, they are gently removed. This can be quite painful and may require sedation of the horse.
• The leg is dried after each cleaning and then topical medications are applied. We like to use Animax ointment which provides antibacterial, antifungal, and anti-inflammatory activity.
• In some cases we wrap the legs initially to keep them clean and dry or may put the horse on an injectable antibiotic as well. Many horses are also put on Bute or Banamine to help with pain.

Some horses suffer from recurrent episodes of pastern dermatitis. In these cases we try to determine an underlying cause by looking at the environment (is the horse in a chronically wet or muddy area) and perhaps doing a biopsy of the skin.