S4052 A Diagnostic Odyssey: Cytomegalovirus Colitis in an Immunocompetent Patient

Introduction: Cytomegalovirus (CMV) colitis is rare in immunocompetent individuals, often leading to delayed diagnosis. CMV, a ubiquitous herpesvirus with a seroprevalence of 40–100% in adults, typically causes asymptomatic or mononucleosis-like illness in healthy hosts. Gastrointestinal involvement is uncommon but can cause significant morbidity. In rare cases, CMV colitis occurs due to primary infection or reactivation in the setting of critical illness, posing diagnostic and therapeutic challenge. Case Description/Methods: A 62-year-old woman with bipolar and schizoaffective disorder, living in a nursing home, presented with altered mental status and persistent watery diarrhea for 3 days. She had no history of immunosuppression, malignancy, or steroid use. Initial workup revealed leukocytosis, hypokalemia, hyponatremia, increased kidney, liver functioning tests and C-reactive protein, lactic acidosis. A FilmArray stool panel and CMV DNA PCR were negative. CT abdomen/pelvis showed bowel wall thickening from the transverse to sigmoid colon with ileus. Flexible sigmoidoscopy revealed a large ulcer in the sigmoid colon, initially suspected to be ischemic colitis. Biopsies were negative for CMV. Persistent diarrhea and an unremarkable autoimmune workup prompted further investigation. A second colonoscopy revealed friable, ulcerated colonic mucosa. Repeat biopsies were positive for CMV, confirming CMV colitis. The patient was treated with intravenous ganciclovir, leading to symptom resolution. Discussion: CMV colitis in immunocompetent individuals is rare and challenging to diagnose due to nonspecific symptoms and initially negative serologic and histologic tests. This case underscores the importance of serial endoscopic biopsies, as early samples may miss focal disease. CMV colitis can mimic ischemic colitis or inflammatory bowel diseases, leading to potential misdiagnosis. While most immunocompetent patients clear CMV without treatment, severe colitis with large ulcers may require antiviral therapy. Recognizing CMV as a potential cause of colitis, even in immunocompetent hosts, can prevent delayed diagnosis and improve outcomes.