Erythema Nodosum as the Primary Manifestation of Acute Histoplasmosis in a Pediatric Patient From an Endemic Region.

Erythema nodosum (EN) is a common form of septal panniculitis that typically presents with painful, erythematous nodules on the lower extremities. While most cases are idiopathic, EN can be triggered by infection, medications, autoimmune and inflammatory pathologies, recent immunization, or malignancy. Commonly, EN has been associated with fungal infections, including Histoplasma capsulatum, a dimorphic fungus endemic to the Ohio and Mississippi River Valleys. Although pulmonary involvement is the most common manifestation of the fungal infection, extrapulmonary presentations can occur. We present a case of a nine-year-old immunocompetent male patient from an endemic region who developed EN in the absence of any pulmonary symptoms or radiographic abnormalities. Serologic testing was notable for elevated H. capsulatum antibodies, and the patient reported complete resolution with supportive care alone. This case highlights the importance of considering fungal etiologies while maintaining a broad differential diagnosis when evaluating EN, especially in endemic areas.