Clinical course of sarcoids in 61 Franches-Montagnes horses over a 5-7 year period.

BACKGROUND: The progression of equine sarcoids (ES) is notoriously unpredictable. Making a choice for the appropriate treatment is challenging when dealing with milder manifestations of ES.

OBJECTIVE: The aim of this study was to investigate the clinical course of ES in young horses.

ANIMALS AND METHODS: A cohort of 61 ES-affected three-year-old Franches-Montagnes horses and a breed-, age- and geographically matched control group of 75 ES-free peers were examined twice over a period of 5-7 years. Owners and caretakers were queried, using a standardized questionnaire.

RESULTS: More than half of the 38/61 (62%) horses that were ES-affected at the age of three, had become ES-free at the time of follow-up. In 29 of 38 horses, representing 48% of the entire study population, ES lesions had spontaneously disappeared without therapy. When differentiating the clinical types of ES lesions, occult ES underwent complete spontaneous regression in 65% (11/17), while verrucous lesions regressed spontaneously in 32% (9/28). None of the evaluated intrinsic or environmental factors showed a significant effect on the risk for development, regression or exacerbation of ES disease.

CONCLUSIONS: Our results document a surprisingly high rate of spontaneous ES regression for young horses affected with milder manifestations of ES disease. These findings justify a 'wait-and-see' approach in selected cases of occult and verrucous ES, provided that all lesions are closely monitored. Furthermore, results of this study should also be considered when critically assessing treatment effects of therapies directed against ES, especially in the context of uncontrolled studies.