S5004 Successful Induction and Maintenance of Clinical Remission With Adalimumab and Ustekinumab in Steroid-Refractory Collagenous Enterocolitis: A Rare 10-Year Follow-Up Case Report

Introduction: Collagenous colitis (CC) is a variant of microscopic colitis marked by chronic, watery diarrhea that often manifests with normal-appearing colonic mucosa on colonoscopy and a thickened subepithelial collagen band on histology. CC predominantly affects middle-aged to older women, with an incidence of 5–10 per 100,000 person-years and a prevalence of 40–200 per 100,000 adults in North America and Europe. While CC is well-characterized, concurrent small bowel collagen deposition (collagenous enterocolitis [CE]) is exceedingly rare and associated with severe malabsorption. Only limited case reports exist, leaving its etiology and optimal management unclear. We present a rare case of CE successfully managed and maintained in remission with biologics after infliximab non-response. Case Description/Methods: A 56-year-old Hispanic woman presented with an 8-month history of nausea, vomiting, and diarrhea after influenza immunization. Initial inflammatory labs (C-reactive protein, erythrocyte sedimentation rate) were within normal limits. Duodenal biopsies showed patchy villous atrophy and a thickened subepithelial collagenous layer, consistent with collagenous sprue. Symptoms partially improved with daily glucocorticoids, but tapering led to recurrence. Repeat duodenal and colonic biopsies were notable for collagenous duodenitis, ileitis, and colitis, confirming CE. Infliximab was initiated with partial clinical improvement, but persistent histologic inflammation prompted a switch to adalimumab. This led to gradual clinical remission but no histologic improvement. The patient was then transitioned to ustekinumab with sustained clinical remission and histologic improvement in colitis. Discussion: CE represents a rare form of microscopic enterocolitis characterized by profound malabsorption from simultaneous collagen deposition in the small bowel and colon. Its pathogenesis is poorly understood but may involve autoimmune mechanisms. While glucocorticoids, particularly budesonide, are first-line therapy, many patients relapse or require long-term treatment. Our case underscores the role of biologic therapies in steroid-refractory CE, notably highlighting the successful induction of clinical remission with adalimumab and histologic improvement with ustekinumab. Histologic healing is often delayed and may persist even when the patient is symptom-free. However, IL12/23 inhibitors may improve histologic findings as evidenced in our case. Future research should clarify the prevalence, prognosis, and optimal management of this rare condition.