SCRATCHESWritten by Dr. Kate Moga, Olde Towne Equine, Fredericksburg, VA

 

“Clean and dry, clean and dry” is what I tell horse owners after treating a patient with pastern dermatitis.

Scratches, mud fever, and greasy heel are all familiar terms for pastern dermatitis, a common equine skin problem. Technically, pastern dermatitis is not a single disease but a generic skin reaction to a variety of causes. The dermatitis typically involves the back (caudal aspect) of the pasterns, and if not addressed, it can spread to the front of the pastern. Initially signs may be limited to redness and scaling, but they often progress to oozing of fluid (serum) from the skin, matting of hair, and development of crusts. Chronic cases can become very ugly indeed, as the skin becomes thickened and swollen. It may even develop bumpy, mass-like tissue. This condition is very painful for the horse and can cause lameness in some cases.

Scratches is most commonly seen on white-colored hind legs of all equine breeds. It can be unilateral (one-sided) or bilateral (involving both right and left limbs). It may affect all four legs. Many cases seen in our region are from contact allergy and involve a secondary bacterial infection, but other causes include contact irritation from caustic substances, mites, fungal infection, and photosensitization related to pasture plant toxicity. In some drafts , such as Clydesdales and Shires, an immune-mediated problem, which may have a genetic component, is suspected. Some horses seem particularly susceptible to pastern dermatitis, so they should be monitored carefully at wet times of the year, and treatment should begin at the very first sign of inflammation.

Wet-dry cycles in the horse’s environment—morning dew changing to dry, bathing your horse and not drying its legs thoroughly, or rain showers followed by sun—seem to be a predisposing factor.

In addition to a physical exam and thorough history, an initial workup of these cases includes a skin biopsy as well as skin scraping, cytology and fungal culture.

When pastern dermatitis has been diagnosed, I usually begin treatment by clipping the hair from the area and washing it with warm water and a gentle soap such as dilute chlorhexidine (Nolvasan™) or Johnson’s Baby Shampoo. After scabs are softened by the soap, they should picked off in order to expose the underlying skin. After being thoroughly rinsed, the area should be completely dried.  Depending on the severity of the clinical signs, I will medicate with a topical ointment and bandage for 12–24 hours.  Many topical treatments have already been tried before by the client, and in these cases it is not uncommon for the patient to develop contact dermatitis as well. It is therefore important to only use topical therapy that is needed and minimize the use of topical products that might be irritating.

It is idealistic to think that our fields will always stay dry and mud-free and that dew will not form on our grass.  Below are some recommendations that may have to be modified for your horse’s individual environment.

  • If possible keep horses in clean, dry stalls during wet weather.
  • Turn out horses after the morning dew has dried.
  • Use alternative sources of bedding if contact allergy is suspected.
  • Clip excessive hair over pasterns, if present, to decrease moisture retention.
  • Avoid ultraviolet light exposure by stabling or using leg wraps.
  • Keep horses off pastures and paddocks with excess mud, water, or sand.

Systemic antibiotics or steroids may be necessary to provide relief in stubborn cases. Recurrence is common, especially if the underlying cause is not addressed, so it is worth seeking a definitive diagnosis!