Histologic remission: the ultimate therapeutic goal in ulcerative colitis?

Ulcerative colitis (UC) is a disease of the mucosal layer, and activity of the disease is assumed to be related to mucosal appearance. Mucosal healing has emerged as a major therapeutic goal in UC. Whether mucosal healing should be the ultimate therapeutic goal in these patients is unknown. Even when endoscopy suggests mucosal healing, evidence of histologic activity has been observed. Histologic healing requires complete recovery of the colonic mucosa, with absence of inflammation or structural changes. Histologic improvements have been linked with improved clinical outcomes, such as a reduced risk of relapse and need for surgery/hospitalization and a reduced risk of developing cancer. Hence, there is a rationale for aiming for histologic remission in UC. Numerous methods of classification of histologic activity in UC have been proposed, although only some of these are widely used. We review the current definitions of histologic remission, the range of scoring systems most commonly used, and the evidence of histologic improvement that is available from the latest therapies for UC. We also highlight questions that will require careful consideration if histologic remission is to become more widely used as an end point in clinical trials and a treatment goal in clinical practice.