EQUINE | CPD Article
where treatment carries a poor prognosis, some
cases may be best left alone. A small proportion
of sarcoids (<1%) will resolve spontaneously.
Different treatments have different success rates
for the various forms of the disease and many
veterinarians have their own preferred treatments.
• Prognosis: most individual lesions become larger,
more extensive and more aggressive if left alone
(and particularly if traumatized at all) and most
cases will develop increasing numbers of lesions
with time. A few lesions remain static and a few
horses remain with low numbers. In all cases the
prognosis should be very guarded.
• Worldwide.
• Significant geographical variations occur in both
prevalence and types of lesion.
• Multiple lesions are more common in the UK than
in Australia, USA and continental Europe.
• Occult and verrucose lesions are uncommon in
Africa, Australia and North America, but especially
common in the UK.
• There is an increasing prevalence of the condition
worldwide.
Age predisposition
Presenting signs
• The earliest forms appear simply as roughly circu-
lar alopecic skin lesions with a slightly scaly sur-
face texture. Even in these however, small granules
and/or thickened skin can usually be palpated.
• Cutaneous verrucose, nodular or fibroblastic forms
are the most frequent presentations recognized by
both owners and practitioners.
• Numbers of lesions vary from few to many
hundreds or even thousands; single lesions can
occur in a few cases and there is no typical
presentation/type for these single lesions.
• Lesions can be found on any area of the body
but the distal limbs and upper body trunk and
dorsum are probably less often affected. Lesions
are commonly found on the head (especially
periorbital, lips and muzzle), ventral body
(especially paragenital region and axillae).
• Six forms of sarcoid exist - occult, verrucose,
fibroblastic, nodular, mixed and malignant.
• Individual horses may have several different types
of sarcoid lesion and even single anatomical
locations may have several forms concurrently.
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Geographic incidence
• Although most cases are identified first around
2-10 years of age, de novo cases can develop at
any age, at any time, in any horse that is geneti-
cally liable to the condition.
Sex predisposition
• No sex predisposition has been demonstrated
convincingly.
Breed/Species predisposition
• Incidence related to specific genetic susceptibility
associated with the major histocompatibility
complex (MHC) antigen ELA-B1, also ELA-W3,
W5 and W13. Genetic susceptibility relates to the
presence of 'susceptibility' genes.
• Appaloosa, Arabian and Quarterhorses have
been shown in studies to be at a higher risk of
developing sarcoid than Thoroughbreds.
• Standardbred horses have a lower incidence of
sarcoids than Thoroughbreds.
• It is reasonable to assume that all breeds can be
affected.
• Equine Health Update •