D0089 - A Wolf in Sheep's Clothing: Isolated Colonic Histoplasmosis as a Rare and Devastating Disease in Patients Undergoing Immunomodulator Therapy - A Systematic Review

Introduction: Gastrointestinal histoplasmosis is mainly considered a protean manifestation of disseminated histoplasmosis. It can mimic inflammatory bowel disease (IBD), cancer, or other bowel diseases, presenting diagnostic and therapeutic challenges. To our knowledge, this report represents the first systematic review on isolated colonic histoplasmosis in patients receiving immunomodulator therapy (IMT).

Methods: A systematic search of MEDLINE, Google Scholar, Embase, and Scopus was conducted for English-only studies, published between inception and June 15, 2022. Abstracts from major GI conferences and articles’ reference lists were also screened. The search terms “Histoplasma capsulatum,” and ‘‘histoplasmosis’’, were combined using the Boolean operators ‘AND’ and ‘OR’ with the terms “isolated colonic” and ‘’colon’’, with all permutations. Two authors reviewed each study to determine eligibility. The search yielded a total of 264 relevant results. However, only 13 articles fulfilled the inclusion criteria.

Results: A total of 13 patients were identified with isolated colonic histoplasmosis in the setting of IMT. The mean age was 55.62 ± 10.66 years, and 62% of patients were women. Screening colonoscopy incidentally diagnosed histoplasmosis in 38% of patients. Common symptoms were diarrhea 31%, weight loss 23%, or abdominal pain 23%. IMT was mainly administered for liver transplant 31%, renal transplant 31%, and ulcerative colitis 15%. Colonoscopy mostly revealed colonic ulcers 69%, polypoid lesions 15%, or hemorrhage 15%. Of 38%, Histoplasma antigen was positive in 23% of patients. Colonic biopsy diagnosed 85% of patients. Unfortunately, 15% of patients also underwent GI surgery for diagnosis. Amphotericin B with itraconazole 54%, itraconazole alone 38%, and amphotericin B alone was administered in 8% of patients. All patients achieved complete recovery.

Discussion: This systematic review shows that isolated colonic involvement can be the only clinical presentation of disseminated or primary histoplasmosis. Gastroenterologists should consider it in patients undergoing IMT who present with consistent symptoms. GI histoplasmosis should be ruled out before starting immunosuppressive therapy for colitis due to other causes. Colonoscopy with biopsy can play a pivotal diagnostic role in suspected patients (Figure 1). Prompt detection and antifungal treatment can result in uneventful recovery. However, delayed identification and improper treatment can lead to death in immunocompromised individuals.