A retrospective study examined data on cutaneous nodular and proliferative lesions in horses, donkeys and mules submitted to the Veterinary Diagnostic Laboratory at Oregon State University in a 3.5-year period. One hundred and sixteen non-neoplastic nodular and proliferative lesions were identified, comprising 18% of all lesions studied and 6.4% of total equine pathology accessions. Exuberant granulation tissue, eosinophilic granuloma, fungal granuloma, cysts and habronaemiasis were most common, and constituted 91% of non-neoplastic lesions, 16% of all lesions studied, and 5.85% of total equine pathology accessions. Calcinosis circumscripta and cutaneous granulomas, including eosinophilic granuloma, fungal granuloma, and other granulomas, were most common in horses up to 10 years of age. Eosinophilic granuloma was more common in males than in females, and was diagnosed most often in autumn and winter. Fungal granuloma was common in this population and was most often diagnosed in the spring. Habronaemiasis was diagnosed in late summer and early autumn, and was most common in males. Results of this study indicate that equine non-neoplastic nodular and proliferative skin lesions are commonly submitted for histopathologic examination. Results also suggest that regional differences exist regarding incidence of cutaneous fungal granuloma and season of occurrence of eosinophilic granuloma in horses.
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