To Örebro University

BACKGROUND: A definitive diagnosis of Crohn's disease (CD) or ulcerative colitis (UC) is not always possible and a proportion of patients will be diagnosed as inflammatory bowel disease unclassified (IBDU). The aim of the study was to investigate the prognosis of patients initially diagnosed with IBDU and the disease course during the following five years.

METHODS: The Epi-IBD study is a prospective population-based cohort of 1,289 IBD patients diagnosed in centres across Europe. Clinical data were captured prospectively throughout the follow-up period.

RESULTS: Overall, 476 (37%) patients were initially diagnosed with CD, 701 (54%) with UC, and 112 (9%) with IBDU. During follow-up, 28 (25%) IBDU patients were changed diagnoses to either UC (n=20, 71%) or CD (n=8, 29%) after a median of six months (IQR: 4-12), while 84 (7% of the total cohort) remained IBDU. A total of 17 (15%) IBDU patients were hospitalized for their IBD during follow-up, while 8 (7%) patients underwent surgery. Most surgeries (n=6, 75%) were performed on patients whose diagnosis was later changed to UC; three of these colectomies led to a definitive diagnosis of UC. Most patients (n=107, 96%) received 5-aminosalicylic acid, while 11 (10%) patients received biologicals, of whom five remained classified as IBDU.

CONCLUSIONS: In a population-based inception cohort, 7% of IBD patients were not given a definitive diagnosis of IBD after five years of follow-up. One in four patients with IBDU eventually were classified as CD or UC. Overall, the disease course and medication burden in IBDU patients were mild.