Cutaneous clues to a fungal culprit: disseminated Blastomycosis presenting as inflammatory monoarthritis — a Case Report

Blastomycosis is a dimorphic fungal infection caused by Blastomyces dermatitidis and related species, classically presenting with pulmonary and cutaneous involvement. Musculoskeletal manifestations, particularly monoarthritis, are rare and diagnostically challenging. We present the case of a previously healthy 41-year-old man who developed nodular skin lesions, cough, pulmonary nodules and persistent left knee arthritis, initially thought to be due to pseudogout. The diagnosis of disseminated fungal infection was suggested by CT scan, skin biopsy, and confirmatory fungal culture that grew Blastomyces dermatitidis. This case highlights the atypical pattern of joint involvement, the need to expand the differentials as dictated by clinical signs, the role of multidisciplinary collaboration, and the diagnostic utility of skin biopsy and fungal culture.