INFLAMMATORY BOWEL-DISEASE - REEVALUATION OF THE DIAGNOSIS IN A PROSPECTIVE POPULATION-BASED STUDY IN SOUTH EASTERN NORWAY

Background-The incidence figures for ulcerative colitis (UC) and Crohn 's disease (CD) have been difficult to interpret, and geographical var iations may be due to differences in classification criteria and study design. Few studies have based the incidence on prospective systemati c follow up to confirm the initial diagnosis. Methods-Between 1990 and 1993, in a prospective incidence study of inflammatory bowel disease (IBD) in south eastern Norway, 527 cases of UC, 228 cases of CD, 36 ca ses of indeterminate colitis (IND), and 55 cases of possible IBD were identified, yielding an annual incidence of 13 . 6, 5 . 9, 0 . 9, and 1 . 4 per 10(5) respectively. The diagnosis and all clinical data were reviewed by two gastroenterologists independently of each other. One to two years after diagnosis, all patients were offered a clinical fol low up in which the initial diagnosis was assessed. Results-Between th e time of diagnosis and the follow up, 16 patients had died, four of c omplications related to IBD. Of the remaining 830 patients, 98% (814/8 30) were available for follow up, 93% (772/830) attended a clinical ex amination which included a colonoscopy in 77% (637/830), and the remai nder had had a telephone interview, or reassessment based on hospital records, or both. Twenty seven patients were reclassified as not havin g IBD (3%), and 65 patients were characterised as possible IBD (8%). O f the patients initially classified as UC, 88% had their diagnosis con firmed, compared with 91% with an initial diagnosis of CD. In patients with indeterminate colitis, 33% were classified as definite UC and 17 % as CD. This reclassification of patients yielded a corrected annual incidence of 12 . 8 for UC and 6 . 0 for CD. Conclusion-At follow up o ne to two years after the diagnosis of IBD, the initial incidence was only marginally altered. This is probably due to uniform inclusion cri teria and careful diagnostic methods. The study also illustrates the i mportance of the re-evaluation of the initial diagnosis as close to 10 %, both among patients with UC and CD, were reclassified at follow up.