Beyond the Usual Suspects: Gastrointestinal Histoplasmosis as a Marker of Undiagnosed Common Variable Immunodeficiency.

A 28-year-old woman presented with chronic diarrhea, weight loss, and recurrent gastrointestinal infections. Intestinal biopsies unexpectedly revealed Histoplasma capsulatum, prompting immunologic evaluation that demonstrated severe hypogammaglobulinemia and reduced B-cell counts, consistent with common variable immunodeficiency. She improved with intravenous immunoglobulin and antifungal therapy. This case highlights gastrointestinal histoplasmosis as a potential early marker of undiagnosed common variable immunodeficiency and underscores the importance of considering primary immunodeficiency in adults with persistent gastrointestinal symptoms.