BACKGROUND: Disseminated histoplasmosis, a disease that can present years after exposure to the causative organism, may manifest in many diverse ways. Although the gastrointestinal tract is involved in most cases, the initial presentation occurring along the gastrointestinal tract, including the colon and rectum, is infrequent.

CASE REPORT: This case report describes a 66-year-old male patient who presented with an indurated painful perianal lesion that appeared highly suspicious for malignancy on imaging. The patient had no known history of well-established immunocompromised state except for a short course of prednisolone for chronic obstructive pulmonary disease management. A biopsy of the mass was performed, showing chronic inflammation with clusters of epithelioid histiocytes containing characteristic, PAS-fungus stain-positive, intracellular yeast forms consistent with histoplasmosis. There was no evidence of malignancy. A subsequent work-up revealed perihilar nodularity on chest X-ray suggestive of calcified granuloma, a positive Histoplasma Capsulatum Antigen test result, and mildly decreased CD4: CD8 ratio of unknown significance. HIV testing was negative. Treatment with itraconazole and terbinafine was initiated, and at 5-months follow-up, the patient reported significant improvement in signs and symptoms, with undetectable Histoplasma antigen on repeat testing.

CONCLUSIONS: This case represents an extremely rare presentation of histoplasmosis infection, and highlights the fact that presenting symptoms of histoplasmosis can be vague and may mimic other disease processes, including neoplasia. Biopsy of the lesion with PAS staining and serologic testing is critical in establishing the correct diagnosis.

Keywords: Histiocytes, Histoplasmosis, Lower Gastrointestinal Tract, Antifungal Agents, Anus Diseases, Diagnosis, Differential, Histoplasma, Itraconazole, terbinafine