Indeterminate colitis: definition, diagnosis, implications and a plea for nosological sanity.

In 1978, Price introduced the concept of indeterminate colitis to describe cases in which colonic resections had been undertaken for chronic inflammatory bowel disease (CIBD), but a definitive diagnosis of either of the classical types of CIBD, ulcerative colitis and Crohn's disease, was not possible. This was especially apposite in cases of acute fulminant disease of the colorectum. More recently, the term indeterminate colitis has been applied to biopsy material, when it has not been possible to differentiate between ulcerative colitis and Crohn's disease. In our opinion, and in those of other workers in this field, the term should be restricted to that originally suggested by Price. This then provides a relatively well-defined group of patients in whom the implications and management of the disease are becoming much clearer. Cases where there are only biopsies with CIBD, but equivocal features for ulcerative colitis and Crohn's disease, should be termed 'CIBD, unclassified', 'equivocal/non-specific CIBD' or IBD unclassified (IBDU), in line with recent recommendations. When the diagnosis is correctly restricted to colectomy specimens, there is now good evidence that the majority of cases will behave like ulcerative colitis. Furthermore, the diagnosis should not be a contraindication to subsequent pouch surgery. When the latter is undertaken, surgeons and patients can expect an increased complication rate, compared with classical ulcerative colitis, especially of pelvic sepsis, but most patients fare well. Only very occasional patients, around 10%, will eventually be shown to have Crohn's disease. This review describes the pathology of cases appropriately classified as indeterminate colitis and the implications of that diagnosis. It also highlights recent advances in its pathological features, clinical management and its immunological and genetic associations.