Microscopic / “Backwash” Ileitis and its Association with Colonic Disease in New Onset Pediatric Ulcerative Colitis

Background: Microscopic ileitis and its association with pancolitis in adults with ulcerative colitis (UC) has been described. However, the incidence of ileitis and associations with colonic disease in pediatric UC have not been thoroughly investigated. This study was undertaken to examine the prevalence of microscopic ileal inflammation at the time of initial diagnosis in a cohort of children with UC. Methods: We reviewed colonoscopy and biopsy data at time of diagnosis from 105 children and young adults with treatment naïve ulcerative colitis; ileal and colonic mucosal biopsies were available on all patients. Ileal mucosal biopsies were examined for the presence and severity of ileal inflammation, as well as other histologic features. Concurrently obtained colonic mucosal biopsies were assessed to define the severity, distribution, and extent of disease; endoscopic and clinical follow-up data were reviewed. Results: 107 ileal mucosal biopsies and 693 corresponding colonic mucosal biopsies were examined. Seventeen of 105 patients (16%) were found to have ileal inflammation (mean age = 10.4 years, 59% female), 14 (82%) of whom had histologic pancolitis. The presence of ileal inflammation was significantly associated with endoscopic pancolitis (p = 0.02). The association between histologic pancolitis, severity of active inflammation in the cecum and ascending colon suggested a possible association with ileal inflammation (p = 0.06, 0.07, and 0.08 respectively), but did not reach statistical significance. Conclusion: Patients with new onset ulcerative colitis may have microscopic ileal inflammation at time of diagnosis, even if the terminal ileum appears macroscopically normal. The presence of endoscopic pancolitis is associated with the presence of histologic ileitis. In contrast to existing studies in adults, an association between the presence of ileitis and the histologic severity or the histologic extent of colitis was not observed. Children with microscopic ileitis in the context of UC do not need to be reclassified as "indeterminate colitis" or Crohn's disease. Address correspondence and reprint requests to Jeffrey D. Goldsmith, MD, Boston Children's Hospital, Department of Pathology, BCH 3027, 300 Longwood Avenue, Boston, MA 02215, USA (e-mail: jeffrey.goldsmith@childrens.harvard.edu). Received 10 July, 2018 Accepted 6 December, 2018 Source of Funding: None. Relevant Conflicts of Interest: None. The authors report no conflicts of interest. © 2019 by European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology,

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