Unmasking Sapovirus: Chronic Enteritis in an Immunocompromised Adult With Hypogammaglobulinemia.

Sapovirus is a recognized cause of acute viral gastroenteritis, predominantly affecting children and older adults. While typically self-limiting in immunocompetent individuals, sapovirus can result in persistent, severe gastrointestinal illness in immunocompromised patients. Chronic sapovirus enteritis remains underrecognized and lacks standardized treatment guidelines. We report the case of a 69-year-old woman with multiple myeloma and profound hypogammaglobulinemia secondary to chimeric antigen receptor (CAR) T-cell therapy who presented with a 10-month history of chronic watery diarrhea. Imaging revealed features of chronic enteritis, and stool polymerase chain reaction (PCR) identified persistent sapovirus shedding. Endoscopic biopsy showed epithelial apoptosis with histologic features mimicking grade 1 graft-versus-host disease (GVHD) in the absence of prior transplantation. The patient failed to respond to corticosteroids and intravenous immunoglobulin (IVIG). She was subsequently treated with nitazoxanide, resulting in marked clinical improvement, weight gain, and complete clearance of viral shedding at follow-up. She was discharged home on a regimen of monthly IVIG and pegfilgrastim for immune support. This case highlights the challenges in diagnosing and managing chronic sapovirus enteritis in immunocompromised hosts. Impaired mucosal immunity, particularly immunoglobulin A (IgA) deficiency, likely contributes to viral persistence. Histologic findings may mimic GVHD-like injury, further complicating diagnosis. While no Food and Drug Administration (FDA)-approved treatments exist, therapies such as nitazoxanide and immunoglobulin may offer benefit; however, these observations remain exploratory and require further study in larger cohorts.