Diagnostic vs classification criteria of rheumatic diseases

Dr Christian Dejaco is an associate professor in the Department of Rheumatology at the Medical University of Graz (Austria) and author of the European League Against Rheumatism (EULAR) recommendations for the management of polymyalgia rheumatica and large vessel vasculitis.

What is the difference between diagnostic and classification criteria of rheumatic diseases? What should we be aware of when using classification criteria in clinical practice?

Christian Dejaco, MD, PhD: The difference between classification and diagnostic criteria is that classification criteria have been developed for the classification of patients for the purpose of clinical studies, whereas diagnostic criteria are used to diagnose patients in clinical practice.

The danger of using classification criteria is that they should be applied only to a distinct population. For example, the new classification criteria for giant cell arteritis that have been presented at the last conference of the American College of Rheumatology can only be applied to patients that already have a diagnosis of vasculitis—then one can use classification criteria to distinguish between different types of vasculitis and classify giant cell arteritis.

Another problem of many classification criteria is that they have very high specificity, but they usually lack sensitivity. It is because for clinical trials we would like to have a very distinct and specific population, but at the cost of sensitivity for clinical practice.