Atypical distribution of inflammation in newly diagnosed ulcerative colitis is not rare.

Background: Appendiceal orifice inflammation (AOI) is a common 'skip lesion' in patients with ulcerative colitis (UC). However, other skip lesions are less well known.

Objective: To evaluate the atypical distribution of UC lesions, other than AOI, in terms of their frequency, pattern, risk factors and prognostic implications.

Methods: A retrospective analysis of colonoscopic findings and clinical course of 240 adult UC patients who were initially diagnosed at Asan Medical Center (Seoul, South Korea) was performed. #

Results: Of 240 patients, 46 (19.2%) showed an atypical distribution of lesions at initial colonoscopy: eight (3.3%) had rectal sparing (segmental-type UC); and 38 (15.8%) had patchy⁄segmental skip lesions other than AOI. Skip lesions were detected more frequently in proximal segments of the colon than in distal segments (P=0.001). An atypical distribution was more common in patients with AOI (31.3%) than in those without AOI (10.6%; P<0.001). The clinical course of patients with an atypical distribution was not different from that of patients with a typical distribution in terms of remission, relapse, disease extension, colectomy and mortality. In addition, of the 36 patients with an atypical distribution of lesions at diagnosis who underwent follow-up colonoscopy, 24 (66.7%) demonstrated a typical distribution of lesions.

Conclusions: Patchy⁄segmental skip lesions and rectal sparing occur not infrequently in adult patients with newly diagnosed, untreated UC. As such, these features alone should not be considered to be definitive evidence against a diagnosis of UC. There does not appear to be a prognostic implication of an atypical distribution of lesions.