Celiac Disease Emerging After ASCT in Multiple Myeloma: A Rare Diagnostic Intersection and Literature Review.

BACKGROUND: Autologous stem cell transplantation (ASCT) is a standard component of therapy for eligible patients with multiple myeloma. Persistent gastrointestinal symptoms after ASCT are commonly attributed to infection, medication-related toxicity, or disease relapse, whereas autoimmune enteropathies such as celiac disease are rarely considered. CASE PRESENTATION: We report a 53-year-old woman with lambda light-chain multiple myeloma who achieved complete remission after bortezomib, lenalidomide, and dexamethasone induction followed by ASCT and lenalidomide maintenance. Four months after transplantation, she developed persistent diarrhea and a 4-kg unintentional weight loss. Infectious investigations were negative, and imaging and bone marrow assessment showed no evidence of myeloma relapse. Upper gastrointestinal endoscopy demonstrated duodenal villous atrophy, and biopsy findings were consistent with Marsh 3A celiac disease. Serum antitissue transglutaminase IgA was markedly elevated at > 123 U/mL. A strict gluten-free diet resulted in complete resolution of diarrhea within 2 weeks and a subsequent decline in celiac serologic markers. Lenalidomide-associated diarrhea or enteropathy was considered but could not be definitively excluded because treatment withdrawal and rechallenge were not performed. In addition, pre-ASCT celiac serology and HLA-DQ2/DQ8 typing were unavailable. CONCLUSION: This case highlights celiac disease as a rare but clinically important cause of persistent diarrhea after ASCT. Immune reconstitution following transplantation may unmask previously subclinical autoimmune disease. Clinicians should maintain a broad differential diagnosis for posttransplant gastrointestinal symptoms, as early recognition and appropriate dietary intervention can lead to rapid symptom resolution and prevent unnecessary treatment interruption or morbidity.