S3775 Crystalline Colitis: A Rare Adverse Effect of Sevelamer Therapy

Introduction: Sevelamer-induced colitis is considered a rare but increasingly recognized adverse effect of sevelamer use. Although its true prevalence is unknown, a 2014 case series reported sevelamer crystal deposition in the GI tract of 15 patients. It is likely underdiagnosed due to its nonspecific clinical presentation and the need for histopathologic confirmation. We present a case of sevelamer-induced colitis mimicking infectious or ischemic colitis. Case Description/Methods: A 61-year-old man with a history of end-stage renal disease (ESRD) on hemodialysis presented to the hospital with a 1 week history of abdominal pain and bloody diarrhea. Home medications included sevelamer carbonate dosed at 2400 mg 3 times daily. On arrival, he was found to be in new onset atrial fibrillation with rapid ventricular response and required vasopressor support. Laboratory evaluation revealed leukocytosis (WBC 15.8 × 10⁹/L), elevated inflammatory markers (CRP 22.1 mg/dL, procalcitonin 35.91 ng/mL), and an acute drop in hemoglobin (9.8 g/dL from a baseline of 12 g/dL). Computed tomography (CT) imaging showed inflammatory changes in the ascending colon, suggestive of infectious or inflammatory colitis. Stool studies, including Clostridioides difficile and enteric bacterial PCR panel (Salmonella, Campylobacter, Shigella, Escherichia coli, and Shiga toxin), were negative. Colonoscopy revealed severe diffuse inflammation characterized by altered vascularity, erosions, erythema, friability, granularity, loss of vascularity and deep ulcerations in the proximal transverse colon. Histopathology revealed regenerative changes, focal uninflamed erosion, and numerous sevelamer crystals embedded in the mucosa. These findings were consistent with medication-related injury, though ischemia could not be entirely excluded. Given the presence of sevelamer crystals, the medication was discontinued and replaced with lanthanum carbonate. Discussion: Sevelamer-induced colitis should be considered in dialysis patients presenting with unexplained colitis, especially when infectious and ischemic causes have been ruled out. The characteristic histopathologic findings of sevelamer crystals embedded in the colonic mucosa are key to diagnosis. Delayed recognition may lead to unnecessary treatments, prolonged symptoms, and increased morbidity. Early identification and discontinuation of sevelamer, with substitution by an alternative phosphate binder, are essential for symptom resolution and prevention of further gastrointestinal injury.