• Crohn's disease
• Vienna classification
• genetics

I hasten to congratulate Louis et al on their meticulous and insightful study on the stability of Crohn's disease phenotypes according to the Vienna classification (Gut 2001;49:777–82). It was particularly gratifying to learn from them (in a separate communication) of the remarkably high degree of interobserver agreement in classifying patients by this system.

The principal message that the authors draw from their study is that the initial “behavioural” classification of B1 (non-stricturing non-penetrating) at the onset of Crohn's disease hardly ever remains stable over the lifetimes of the patient but almost invariably progresses in time to either B2 (stricturing) or B3 (penetrating) disease. Naturally, this finding hardly comes as a surprise either to the authors of the Vienna classification¹ or in fact to any clinician caring for patients with Crohn's disease. More important and revealing, in my opinion, is the observation by Louis et al that “the proportion of initially B2 patients changing from B2 to B3 was [only] 15.4% (only 2/13 patients)”.

Therefore, once “inflammatory” (B1) disease has made its almost invariable progression …