S5014 Adverse Gastrointestinal Symptoms and Inflammatory Bowel Disease Secondary to Enteric Coated Mycophenolate Sodium

Introduction: Gastrointestinal symptoms are a common side effect of the immunosuppressant drug mycophenolate mofetil (MMF), prompting the development of enteric coated mycophenolate sodium (MPS). MMF has also been shown to cause changes in bowel histology mimicking inflammatory bowel disease, bowel ischemia, and graft vs host disease, with limited evidence of whether MPS leads to these changes as well. Here we present a novel case of persistent diarrhea and histological mimicry of inflammatory bowel disease due to use of MPS. Case Description/Methods: Twenty-two-year-old woman with history of linear morphea and irritable bowel syndrome who was on treatment with methotrexate and prednisone developed worsening of her morphea in October 2024. She was given another course of steroids and started MMF in addition to methotrexate. Due to immediate abdominal discomfort from MMF, she was switched to MPS a week later. In January 2025, the patient was seen by her dermatologist and reported 4-5 episodes of diarrhea per day with 18 lb weight loss. She was referred to gastroenterology for further evaluation. Her stool calprotectin was 125 mcg/g. She underwent colonoscopy in March 2025 which showed patchy mild inflammation with congestion, erythema, granularity throughout the colon with biopsies showing moderately active colitis w/ crypt apoptosis and crypt distortion. A video capsule endoscopy was normal. After discussion with her dermatologist, the MPS was discontinued with plan to switch to upadacitinib. At follow-up, she reported improvement in diarrhea after discontinuation of MPS, noting more formed stools. Discussion: MMF is often switched to MPS to reduce adverse gastrointestinal symptoms. Several studies suggest that patients experience less GI side effects and subsequently less likelihood of dosing changes or discontinuations with the latter. Histological changes due to MPS have been less so studied. This is a unique case of a patient with frequent diarrhea corresponding with the same time frame as MPS use, with notable improvement after discontinuation. Of note, the patient had underlying irritable bowel syndrome but there was a clear worsening of her symptoms with weight loss after initiation of MPS and resolution on stopping the medication. Biopsies showed histology mimicking inflammatory bowel disease, a known sequelae of MMF, during use of MPS. This case demonstrates that while rare, MPS may cause colitis similar to that caused by MMF.