here - Australian College of Veterinary Scientists

Clinical approach to the horse with
pastern dermatoses
Janet Littlewood
Crusting and scaling lesions affecting the skin of the distal limb of horses presents a
diagnostic and therapeutic challenge to the equine practitioner and dermatologist
alike. The use of various colloquial descriptive terms such as “greasy heel”,
“scratches” and “mud fever”, which horse owners frequently view as a definitive
diagnosis, further serves to confuse the issue. At best, these terms should be viewed
as describing a clinical syndrome, for which there are a number of underlying
aetiologies. Whilst empirical remedies may be effective in managing such cases, a
significant number fail to respond to such therapies and can cause frustration to
client and clinician alike, as well as being a significant welfare problem to the patient
in some instances. The efforts of the attending clinician should be directed towards
identifying underlying predisposing factors and pathogens and implementing specific
therapy to eliminate the problem. Appropriate samples taken at the outset will
minimise the risk of a chronic, recurrent skin problem whose features may be
changed by the intervening therapy, making it harder to reach a definitive diagnosis
later. The client is more likely to be impressed by attempts to make a proper
diagnosis at the outset, so that correct treatment can be initiated and, hopefully,
resolution achieved sooner.
There are a number of factors that may predispose to grease heel syndrome,
including genetic factors such as presence of feathers in heavy breeds and nonpigmented
skin; environmental factors such as moisture, prevailing climate and
management practices; and iatrogenic factors including tack items and topical
preparations, which are frequently utilised by horse owners. Primary causes of grease
heel syndrome include physical and chemical irritants and infectious agents such as
mites and dermatophytes. The extremities may be affected by extreme cold
(frostbite) and ultraviolet light exposure may result in photodermatoses in nonpigmented
limbs. Bacterial infection is common in grease heel syndrome, but
whether this represents a true primary pyoderma or, as in the dog, a secondary
phenomenon, is not clear. Progressive pathology with fibrosis is a particular problem
of diseases of the distal equine limb and chronic lesions may be characterised by
irreversible changes.
The differential diagnosis for crusted papules, often with “paintbrush” tufting or
matting of hair, includes dermatophilosis, dermatophytosis and staphylococcal
(pastern) folliculitis. Cytological preparations are invaluable and are often diagnostic
in acute, exudative lesions, with causal organisms identifiable in impression smears
of underside of scabs or crusts. Bacterial and/or fungal culture are helpful in
identifying actual species involved, although it should be noted that Dermatophilus
ACVSC Proceedings Dermatology Chapter Science Week 2005 55