Update for indeterminate colitis

The distinctive diagnosis of Crohn's disease (CD) and ulcerative colitis (UC) is based on a combination of clinical, histologic, endoscopic, and radiologic data. Both UC and CD show characteristic, but non-specific, pathological features that may overlap and result in a diagnosis of indeterminate colitis (IC), which was proposed by pathologists for colectomy specimens in 1978, usually from patients operated on for severe colitis, especially in cases of acute fulminant disease of the colorectum. The subgroup of patients with an uncertain diagnosis has been classified as IC. Later, the same terminology was used for patients showing no clear clinical, endoscopic, histologic, or other features allowing a diagnosis of either UC or CD. More recently, the term IC has been applied to biopsy material when it is not been possible to differentiate between UC and CD. However, this term IC has suffered varying definitions, which in addition to numerous difficulties in diagnosing inflammatory bowel disease, has led to much confusion. In resected specimens, the term colitis of uncertain type or etiology is preferred. Over time, the majority of patients remain with a diagnosis of IC or show symptoms similar to UC. Ileal pouch anal anastomosis can be performed in such patients, with outcomes of pouch failure and with functional outcomes that are similar to those in patients with UC, but with increased risk of postoperative pouch complications. This review addresses the definition of indeterminate colitis, its pathology, its natural history, and the outcomes of restorative proctocolectomy.