Frequency and clinical evolution of indeterminate colitis: a retrospective multi-centre study in northern Italy

Objective To evaluate the prevalence and the clinical evolution of patients with an initial diagnosis of indeterminate colitis. Design Retrospective, observational study. Setting Fifteen gastrointestinal units in northern Italy. Participants Patients with an initial diagnosis of indeterminate colitis seen between 1988 and 1993. Interventions Patients were traced through a common database and centres were requested to update their clinical follow-up. Main outcome measures Frequency of patients with an initial diagnosis of indeterminate colitis among those with IBD; rate of patients who subsequently had a definite diagnosis of either Crohn's disease or ulcerative colitis. Results Fifty out of 1113 IBD patients (4.6%) had been diagnosed as having indeterminate colitis. During follow-up, 37 patients (72.5%) had a definite diagnosis of either Crohn's disease or ulcerative colitis. The cumulative probability of having a definite diagnosis of either ulcerative colitis or Crohn's disease was 80% 8 years after the first one (i.e. the first diagnosis). The probability of having a diagnosis of Crohn's disease was increased in patients with fever at onset, segmental endoscopic lesions or extra-intestinal complications and in current smokers. The probability of having a diagnosis of ulcerative colitis was increased in patients who had not undergone appendectomy before diagnosis. Conclusions In our area, indeterminate colitis accounts for about 5% of initial diagnoses of IBD. In about 80% of patients, a diagnosis of either ulcerative colitis or Crohn's disease is made within 8 years. Several clinical and demographic features can help in identifying those patients more likely to have a subsequent diagnosis of Crohn's disease and those more likely to have a subsequent diagnosis of ulcerative colitis.