Equine cutaneous fungal granuloma: a study of 44 lesions from 34 horses

Abstract

Forty-four nodular and noninvasive cutaneous fungal granulomas were identified in 34 horses over a 14.5-year period. Cutaneous fungal granulomas were most common in young horses (mean age 6.1 +/- 4.2 years; range 1-19 years). There was no apparent breed or sex bias. Granulomas were either single or multiple, and most often occurred in the skin of the head and neck. The characteristic histological finding was a nodular dermal mass with a mean diameter of 7.3 mm (range 2.5-20 mm) and an intact overlying epithelium. Lesions most often exhibited intense lymphocytic inflammation, with admixed pyogranulomatous inflammation associated with a small to moderate number of fungal elements. Causative fungi were both pigmented and nonpigmented organisms of variable morphology. Penetrating plant material was identified in three cases. Granulomas caused by nonpigmented fungi were most common in horses from wet regions. Both pigmented and nonpigmented fungi were found in granulomas from horses in dry regions. Cutaneous fungal granulomas occurred in February through November, with peaks in April and July. No correlation of yearly incidence with annual average temperature or rainfall was detected. This study confirms that equine cutaneous fungal granuloma is relatively common in horses in the Pacific Northwest. Morphology of causative fungi was variable, but the signalment, history, and clinical and overall histological features were very similar. Surgical excision was curative.