Impending megacolon: small bowel distension as a predictor of toxic megacolon in ulcerative colitis

Abstract

We have read with great interest the recent excellent review by Di Sabatino et al. [1] on ulcerative colitis (UC). We fully agree with their description that toxic megacolon is a life-threatening complication in severe UC, and that a standard plain X-ray study is useful to evaluate the degree of intestinal distension. In clinical settings, delay of surgery sometimes bears a poor prognosis when patients may not fulfill the clinical criteria for toxic megacolon by Jalan et al. [2] or definitive colonic dilatation. We recently experienced a case of ‘impending’ megacolon in a patient with UC, highlighting small bowel distension as a predictor of toxic megacolon. A 27-year-old man with UC presented with sudden onset of severe abdominal pain after 5 weeks’ duration of relapse with hematochezia. He had experienced multiple relapses of pancolitis and was being treated with 750 mg of oral mesalazine three times a day for over 6 years since the first presentation of colitis. On examination, the temperature was 37.6 C. Abdominal examination revealed a distended and tender abdomen with marked rebound and hypoactive bowel sounds. The clinical activity index was elevated up to 19. Laboratory tests showed an increased white blood cell count of 17,400/lL and a C-reactive protein of 8.36 mg/dL. A supine abdominal X-ray study (Fig. 1) showed a notable dilatation of the small intestine with a maximum internal diameter exceeding 4 cm (arrows) as well as indistinct colonic distension (arrowheads). He was diagnosed as having impending megacolon of UC, and therefore underwent subtotal colectomy with end ileostomy. Histopathological examination revealed severe transmural inflammation of the colon. He had an uneventful post-surgical course. Toxic megacolon, a life-threatening complication of UC and diverse colitis, is defined as nonobstructive hypotonic dilatation of the colon, classically exceeding 5.5 cm in diameter in the transverse colon on supine abdominal X-ray [3]. The pathogenesis for megacolon seems to be the excessive colonic production of inflammatory mediators that inhibit colonic motility and nitric oxide, as the key nonadrenergic, noncholinergic neurotransmitter induces colonic muscle relaxation. Recent studies indicate that the finding of persistent small bowel distension on plain abdominal radiograph characterizes a subgroup of patients at high risk for the development of toxic megacolon and multiorgan dysfunction, termed ‘impending’ megacolon [4, 5]. Gaseous distension in the uninflamed stomach and small intestine may precede colonic dilatation presumably due to the increased release of the above inflammatory mediators. The distension can result from the activation of extrinsic intestine–intestinal inhibitory reflexes, which induce paralytic ileus [5]. In conclusion, although the clinical entity of ‘impending’ megacolon has not been established yet, we highlight small bowel distension as a reliable predictor of toxic megacolon, called ‘impending’ A. Hokama (&) K. Kishimoto J. Fujita Department of Infectious, Respiratory and Digestive Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa 903-0215, Japan e-mail: hokama-a@med.u-ryukyu.ac.jp