Colonic Involvement in Disseminated Histoplasmosis of an Immunocompetent Child: A Case Mimicking Crohn’s Disease

Summary: Infection with Histoplasma capsulatum can lead to disseminated disease involving the gastrointestinal tract presenting as diffuse abdominal pain and diarrhea which may mimic inflammatory bowel disease (IBD). We report a case of 12-year-old boy with presumptive diagnosis of Crohn’s disease (CD) who presented with several months of abdominal pain, weight loss and bloody diarrhea. Colonoscopy showed patchy moderate inflammation characterized by erythema and numerous pseudopolyps involving the terminal ileum (Figure A), cecum, and ascending colon. Histologic sections from the colon biopsy revealed diffuse cellular infiltrate within the lamina propria with scattered histiocytic aggregates, and occasional non-necrotizing granulomas (Figures B-C). Grocott-Gomori’s Methenamine Silver staining confirmed the presence of numerous yeast forms suggestive of H. capsulatum (Figure D), further confirmed with positive urine antigen (6.58 ng/mL, range 0.2 - 20 ng/mL) and serum antibody (35.9 EU) to H. capsulatum. Intravenous amphotericin was administered then transitioned to oral itraconazole. Follow-up CT imaging showed a left lower lung nodule and mesenteric lymphadenopathy consistent with disseminated histoplasmosis infection. Gastrointestinal involvement with H. capsulatum with no accompanying respiratory symptoms is exceedingly rare and recognition is often delayed due to the overlap of symptoms with manifestations of IBD. This case illustrates the importance of excluding infectious etiologies in patients with “biopsy-proven” CD prior to initiating immunosuppressive therapies. Communication between clinicians and pathologists is crucial as blood cultures and antigen testing are key studies that should be performed in all suspected histoplasmosis cases.