Isolated perianal Crohn disease: the next challenge is long-term surveillance

To the Editors: I read with great interest the pilot study by Wanchaitanawong and colleagues validating the TOpClass diagnostic criteria for isolated perianal Crohn disease (ipCD).1 Their study provides encouraging validation of the TOpClass framework and identifies additional fistula characteristics that may further improve its diagnostic sensitivity.1 Perhaps the most important question raised by this study, however, extends beyond diagnosis alone. Recognition of ipCD as a distinct clinical phenotype does not necessarily predict its long-term biological behavior. In the cohort of participants in this study no patients developed luminal Crohn disease during a median follow-up of 26 months.1 This finding, although it supports the short-term performance of the proposed criteria, should not be interpreted as evidence that luminal progression is uncommon. While the results are reassuring, the follow-up duration may have been insufficient to allow the determination of whether ipCD remains isolated over the longer term or instead represents the earliest manifestation of luminal disease in a proportion of patients.