My colleague’s e-mail made the assertion that we had set out to do classification and not diagnostic criteria for vasculitis. The diagnostic criteria would come later. Even with a cast on, I had qualms about this. Why? Once, all the disease criteria in our discipline were diagnostic. These were the days of authoritative, eminence-based, ad hoc criteria. The prototype was the Jones criteria for rheumatic fever. Then we began to learn about sensitivity and specificity. The criteria began to be data based—the ACR criteria set for systemic vasculitis is an example. It soon became apparent, however, that these criteria were of limited use in an actual clinical setting. The response was ready: Such criteria were not for diagnosis of the individual patient but were mainly for research studies, enrolling well-defined groups of patients in drug trials or for other clinical and laboratory studies. Nobody questioned why we felt that we had to have an exact diagnosis each time we planned the care of an individual and we could be less precise when we did research. The sophisticated cliché became that criteria available were for classification only. Parallel to this assertion has been the cliché of hope that we would prepare a separate diagnostic criteria set. This is what our vasculitis expert group was and is trying to do.
To me, there is actually no difference in the mental or mathematic activity in the formulation of criteria for diagnosis, classification, or both. Diagnosis, to me, is nothing more than classification in the individual patient.5 The comparator groups, the odds ratios, and the pretest probabilities are there in either exercise, whether we do them by an electronic computer or by our brain, as reading Blink has taught me. Further, the assumption that we should always be more precise in making a diagnosis than when enrolling a patient into a clinical trial may not have as sound a basis as we generally assume.
What It Means to Diagnose in Rheumatology
Why do we need diagnostic or classification criteria in rheumatology? The immediate answer is that we do not have histologic, laboratory, or radiologic leads to accurately define many of our diseases. Equally important is the question of why we want to diagnose or classify in the first place. According to Webster’s Dictionary, the verb diagnose is originally Greek, and the best synonym is discern. It also has the connotation of “understanding the nature of.” The verb classify, on the other hand, is newer; its first use is in the English language was at the end of 18th century and simply means to put into classes. As such, it implies less precision and perhaps less of an anxiety “to know the nature of.” So, when we do research we like to classify, and when confronted with a patient we prefer to diagnose. In other words, with a patient, we are not content with a classification only, we also want to attach an “omniscience” to what we classify. We, as rheumatologists, painfully know we do not know the exact nature of many of the ills we recognize and manage—rather successfully in recent times, at that. Perhaps we should be more open about this, first to ourselves, then to our patients, and finally to the public.
To me, there is actually no difference in the mental or mathematic activity in the formulation of criteria for diagnosis, classification, or both. Diagnosis, to me, is nothing more than classification in the individual patient.
Let us now take this line of thought into a recent undertaking in our discipline, the new ACR/European League Against Rheumatism (EULAR) rheumatoid arthritis (RA) criteria set. Between you and me, we still do not know what causes, propagates, and, in a few patients, even heals RA. Most probably it is more than one disease. However, in recent years we have been quite successful in our management of what we diagnose or classify as RA.
