3155 Macroscopic to Microscopic: A Case of Crohn's Disease Progressing to Collagenous Colitis

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INTRODUCTION: Microscopic colitis (MC), sub-typed into lymphocytic and collagenous colitis is characterized by normal endoscopic/macroscopic/radiologic colonic mucosa but abnormal histological findings and presents as chronic, non-bloody diarrhea mostly in elderly females. Association of MC with inflammatory bowel disorders (IBD), Crohn's or Ulcerative colitis is unclear and has been rarely reported. Herein, we present a patient with Crohn's disease with eventual progression to MC. CASE DESCRIPTION/METHODS: 56-year-old female presented with 12-day non-bloody diarrhea with nocturnal symptoms, weight loss, and diffuse cramping abdominal pain. No fever, sick contacts, travel, food contamination, recent antibiotics or new medications. CT Abdomen/Pelvis was normal. Labs showed leukocytosis, elevated CRP and fecal-calprotectin. Colonoscopy showed inflammation characterized by congestion, granularity, cobblestoning of mucosa from the rectum to the transverse colon. The IC valve was stenotic and difficult to intubate. Biopsy showed mild-chronic active colitis without granulomas or dysplasia. CT Enterography showed narrowing of TI and two other small bowel segments. The patient was started on steroids for possible Crohn's disease and bridged to Adalimumab. Despite being compliant, the patient was re-admitted with 10-day non-bloody diarrhea after 2-3 months. Colonoscopy showed improved endoscopic inflammation but biopsies revealed collagenous microscopic colitis. Trials of budesonide, cholestyramine, bismuth and loperamide along with Adalimumab were unsuccessful. The patient was on SSRI, which was discontinued. The patient continued to be symptomatic. Repeat colonoscopy showed endoscopically benign mucosa and continued presence of collagenous colitis on biopsy. Given the refractoriness of the patient's symptoms, she was referred to IBD specialist at a tertiary center. DISCUSSION: Concomitant presence of MC with IBD or progression of one condition to other is rare and the pathogenesis is unclear. It is hypothesized that IBD and MC may share common pathophysiologic pathway, but there is no clear data. A study proposed increased Th1/Tc1, TNFα-producing cells, and a subset of Th2/Tc2 cells, to be involved in MC-to-IBD transformation. The clinical relevance of our case is to emphasize the consideration of MC in a patient with UC or CD, who develops chronic, non-bloody diarrhea. Mucosal biopsies should be obtained to rule out MC. Once confirmed, the management should be adjusted accordingly.

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