S3847 A Case of Mycophenolate Mofetil-Induced Colitis in a Patient With Lupus Nephritis

Introduction: Mycophenolate mofetil (MMF) is a potent immunosuppressive agent widely used in therapeutic regimens for autoimmune conditions, such as systemic lupus erythematosus (SLE) and myasthenia gravis, as well as in post-solid organ transplant periods to counter allogenic graft rejection. MMF-induced colitis is a serious complication seen in post-transplant patients on chronic immunosuppression but infrequently reported in autoimmune disorders. Here we present a case of a young woman with SLE and active lupus nephritis presenting with MMF-induced colitis. Case Description/Methods: A woman in her twenties with a known history of systemic lupus erythematosus (SLE) was sent from the nephrology clinic to the emergency department with progressive anasarca, nausea, pruritus, and chronic diarrhea for the past 6 weeks. She was treated with high-dose glucocorticoids and an intensified dose of mycophenolate mofetil (MMF), which was increased from 250 mg twice daily to 1000 mg 3 times daily (3 grams/day) as induction therapy for a flare of biopsy confirmed lupus nephritis, with partial improvement in renal function. She continued to experience increasingly frequent diarrheal episodes (up to 10 times a day), 2 weeks after increasing the dose of MMF. She reported passing large volume, watery, non-greasy, and non-foul-smelling loose stools, without gross admixture of blood, mucus, or pus. The stool workup was positive for the guaiac test but otherwise negative for infectious etiologies. Biopsies taken from the ascending colon, transverse colon, and sigmoid colon revealed fragments of benign colonic mucosa demonstrating pathologic features consistent with mycophenolate mofetil toxicity. Discussion: Mycophenolate mofetil (MMF) is widely used as an induction agent for lupus nephritis due to its immunosuppressive efficacy and a relatively acceptable toxicity profile. MMF has been shown to reduce the steroid requirement and the number of subsequent disease flares. However, gastrointestinal side effects, particularly diarrhea and colitis, are more commonly observed with MMF. Given that MMF-induced colitis can closely mimic conditions such as inflammatory bowel disease (IBD) or graft-versus-host disease (GVHD), it is essential to pursue diagnostic evaluation, particularly colonoscopy with biopsies, to exclude these ‘mimics’ or coexisting pathologies. Simply discontinuing MMF without a thorough investigation may be inappropriate or even unsafe in cases where active IBD or GVHD is a diagnostic consideration.