Endoscopic and Biomarker Workup of Post-CAR T Diarrhea

In this segment the panelists, Dr. Samir Parekh and Dr. Saurabh Mehandru, of Mount Sinai in New York, work through the diagnostic approach to persistent diarrhea after chimeric antigen receptor (CAR) T-cell therapy for relapsed multiple myeloma. Dr. Mehandru cautions that patients conditioned by years of myeloma treatment often assume diarrhea is unavoidable, which delays recognition, and urges clinicians not to treat unexplained diarrhea as par for the course. He recommends a formal diarrhea evaluation covering infectious and non-infectious causes and small versus large bowel involvement, followed by early endoscopy with biopsies from both the duodenum and the colon and ileum. Dr. Parekh adds that infectious workup should include cytomegalovirus, Clostridioides difficile, and common bacterial pathogens. On non-invasive markers, Dr. Mehandru points to undetectable immunoglobulin A and prolonged suppression of soluble B-cell maturation antigen in blood, and to fecal calprotectin, which is more sensitive to colonic than small bowel inflammation. He describes the syndrome as uncommon but increasingly recognized as CAR T-cell use widens, and both panelists emphasize that the great majority of patients do well and that the risk should not dissuade clinicians from an effective therapy.