S5097 Colonic Clue to a Hidden Diagnosis: Isolated GI Histoplasmosis in an Unaware HIV Patient

Introduction: Histoplasmosis is an opportunistic fungal infection primarily affecting immunocompromised individuals, particularly those with AIDS. While pulmonary involvement is most common, gastrointestinal (GI) manifestations are rare and often underrecognized. This case of disseminated histoplasmosis is notable for its presentation with isolated GI symptoms, highlighting the need for awareness of atypical presentations to ensure timely diagnosis and management. Case Description/Methods: A 32-year-old man with a history of recurrent esophageal candidiasis presented with fever (103.1°F), nausea, vomiting, and 30-pound weight loss over a year. On arrival, he was tachycardic, with a blood pressure of 137/87 mmHg.. Empiric vancomycin and piperacillin-tazobactam were started for suspected sepsis. Due to pancytopenia and transaminitis, doxycycline was added for possible tick-borne disease which is endemic to the patient's region, and intravenous fluconazole was added to cover for candidiasis. A computed tomography (CT) abdomen/pelvis showed right upper quadrant fat stranding, suggestive of duodenitis or pancreatitis. CMV titers were elevated, though polymerase chain reaction was negative. Human immunodeficiency virus (HIV) enzyme-linked immunosorbent assay (ELISA) was positive, with a viral load of 1,881,584 and CD4 count of 25. Endoscopy revealed gastritis and colonoscopy showed a 13 mm ulcer in the ascending colon and mild inflammation in the transverse colon. Biopsy showed necrotizing granulomas with positive fungal stains. Histoplasmosis urine antigen was positive. Lumbar puncture was unremarkable. Subsequently, the patient was started on antiretroviral therapy (bictegravir, emtricitabine, tenofovir) and Amphotericin B, followed by itraconazole. After 2 months, liver function test normalized, the viral load dropped down, the CD4 count improved, and GI symptoms resolved. Discussion: Disseminated histoplasmosis poses diagnostic challenges due to its nonspecific presentation. Isolated GI involvement is extremely rare and can mimic other common conditions like inflammatory bowel disease. In such patients, GI histoplasmosis should be considered early, especially prior to initiating immunosuppressive therapy. This case highlights the importance of considering histoplasmosis in patients without known immunosuppression and unexplained GI symptoms, as it may be the first clue to undiagnosed HIV and delays in diagnosis can have serious consequences. AI was used to refine language only.