Delayed diagnosis of primary cutaneous histoplasmosis in a patient receiving tumour necrosis factor alpha inhibitor therapy

Primary cutaneous histoplasmosis (PCH) is a rare fungal infection, often misdiagnosed due to its polymorphic skin manifestations. We describe a woman in her 60s with rheumatoid arthritis receiving infliximab and long-term prednisone who presented with progressive, non-healing lesions of the left forearm. Initially treated as cellulitis without improvement, further investigation led to a diagnosis of PCH due to Histoplasma capsulatum confirmed by fungal culture. She was treated with systemic antifungal therapy with clinical resolution. This case underscores the importance of considering endemic fungal infections in immunocompromised individuals with persistent skin lesions, the value of early biopsy with cultures and careful management of immunosuppression.