here - Australian College of Veterinary Scientists

the pathology labs was for granulomatous skin. Recently, a group of 7 horses were
investigated which had primary pulmonary disease and no reported concurrent
dermatologic symptoms (Pusterla and others 2003). All of these horses showed
granulomatous lesions in the lungs, which formed the inclusion criterion for the
report. Cutaneous signs may not have been present, not mentioned specifically or
overlooked due to the gravity of the systemic disease. There may be significant
similarity between human and equine sarcoidosis and the disease may present with a
spectrum of clinical signs. Dermatologic lesions may be on one end of the spectrum
and pulmonary lesions on the other.
Sarcoidosis is a rare disease in equine medicine and the pathogenesis is unclear. In
human medicine, histopathologic findings of sarcoidosis resemble those seen in
tuberculosis. Furthermore, tuberculosis shows an increased incidence in patients
with sarcoidosis. As long as 35 years ago, a role for atypical mycobacteria was
presented (Mankiewicz 1964). By using molecular biologic methods, DNA from M.
tuberculosis and an unidentified nontuberculous mycobacterium was identified in
tissue sections and bronchial washings of some patients with sarcoidosis (Fidler and
others 1993). Multiple species of mycobacteria were detected by polymerase chain
reaction (PCR) predominantly from samples of the lymph nodes and pulmonary
tissue (Li and others 1999). These findings support a potential role of mycobacteria
in the pathogenesis of sarcoidosis in some human patients. However it must not be
thought to be the exclusive infectious agent as recent studies in Japan and Europe
suggest that Propionibacterium spp. may also be involved in the aetiology of sarcoidosis
(Eishi and others 2002). Infectious agents could not be detected in horses by culture,
electron microscopy, animal inoculation, direct immunofluorescence or
immunoperoxidase testing (Heath and others 1990, Scott 1991, Stannard 1987, von
Tscharner and others 2000). In three previously reported cases positive titers to
Borrelia burgdorferi were shown (Rose and others 1996). In a recent report, paraffinembedded
skin specimens from 8 horses with sarcoidosis were evaluated with special
stains and PCR assays for Mycobacteria spp., Borrelia burgdorferi, Coccidioides immitis,
Cryptococcus neoformans and Corynebacterium pseudotuberculosis to no avail (Spiegel and
others 2005). There are anecdotal reports about improvement of the condition in
horses which were moved from one state to another (personal communication Tony
Stannard). It was hypothesized that the beneficial effect of relocation was due to
differences in environmental concentrations of mould spores which may play a role
in the pathogenesis of the disease. None of the horses included in this study had a
correspondent history.
In humans, massive immunosuppressive doses of glucocorticoids are the treatment
of choice for sarcoidosis with significant systemic involvement (Braverman 2003).
Cutaneous lesions generally respond to therapy for systemic involvement, but often
recur when the dosage is lowered or discontinued. Patients without systemic
involvement are typically not treated with glucocorticoids. There are anecdotal
reports of success with chloroquine (Zic and others 1991), hydroxychloroquine
(Jones and others 1990), methotrexate (Lower and others 1995), minocycline
(Bachelez and others 2001), thalidomide (Calderon and others 1997, English and
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ACVSC Proceedings Dermatology Chapter Science Week 2005