Criteria for Behçet's disease with reflections on all disease criteria.

With no specific histologic, laboratory or imaging features the diagnosis/classification of Behçet's Disease (BD) remains clinical. As such, disease criteria are needed. The International Study Group Criteria set is the most widely used. It has some limitations, especially in telling BD from Crohn's disease. On the other hand the main issue, as it also applies to many of the other criteria sets in rheumatology, is our lack of appreciation of a list of misconceptions--some examples of which are unluckily also found in the 2010 ACR/EULAR RA Criteria set--about diagnostic/classification criteria making and their implementation. 1. The view that classification and diagnostic criteria should be different is ill advised in that the cerebral/arithmetic basis of both are the same. 2. The default promise of diagnostic criteria to come once we formulate a classification criteria set is an extension of the previous misconception. 3.Taking pains to avoid circularity in criteria making is unwarranted since the essence of criteria making is circular. In addition we fail to exploit the utility of the disease criteria in ruling out, rather than ruling in, the diseases we seek. Finally we also fail to appreciate the paramount importance of the Bayesian prior (the pretest) probability in formulating and implementing these disease criteria. To formulate criteria tailored to subspecialties, as well as giving the often forgotten family history more importance in our criteria sets are some ways to improve the prior probability on which our diagnostic/classification decisions will be based. We first have to reconcile with ourselves that probabilities are very important in our practice and research. Moreover that reconciliation must also be shared with the public, which includes our patients.