Provisional diagnostic criteria for polymyalgia rheumatica: moving beyond clinical intuition?

In 1964, US Supreme Court Justice Potter Stewart, a master of words, when trying to define hardcore pornography admitted, “I could never succeed in intelligibly doing so, but I know it when I see it. . . .” Polymyalgia rheumatica (PMR) has been in that sense the pornography of rheumatic diseases—a difficult to define syndrome of inflammatory pain and stiffness in older people, but one commonly encountered in practice, and not commonly missed by experienced clinicians. The response to low doses of corticosteroids is often rapid, dramatic, and has been used by many clinicians as a feature that helps define the disease. No single clinical finding or laboratory abnormality is unique to this disorder, and although some aspects of cytokine abnormalities and histopathologic findings in this disorder are understood, there is no single identifiable etiopathogenesis. The rather recent history of PMR is one of many names and definitions, reflecting this uncertainty about the pathology and pathogenesis (1). In this issue of Arthritis & Rheumatism, Dasgupta and colleagues (2) report provisional classification criteria for PMR. In a study jointly sponsored by the European League Against Rheumatism and the American College of Rheumatology the authors propose a set of “provisional” classification criteria. These emerged as the result of a multiphase effort in which they initially developed candidate criteria through a systemic literature review, then a consensus process and wider survey. These criteria were then assessed by experts, and those that emerged as most widely agreed upon were reviewed by both rheumatologists and nonrheumatologists in a wider survey generating a number of criteria most widely accepted. They then evaluated the performance of these proposed criteria in a 6-month prospective cohort study of 125 patients with new-onset PMR and 169 non-PMR control patients whose clinical presentation included features that can mimic PMR. They assessed the accuracy of the initial diagnoses at 6-month followup and assessed the relative performance of the individual proposed criteria for discriminating PMR from other conditions. As a prerequisite, based on consensus of experts, all patients with PMR had to be 50 years old and have elevations of C-reactive protein (CRP) and/or the erythrocyte sedimentation rate (ESR) (although the extent of those elevations was not defined). The proposed criteria are found to have a 68% sensitivity and a 78% specificity for discriminating PMR patients from comparison controls. In an explorative substudy, the authors evaluated the use of ultrasound in a scoring algorithm for classifying patients with PMR and found a poor capacity for discriminating shoulder conditions in PMR and rheumatoid arthritis, the latter probably posing the most important differential diagnostic challenge in this age group. Moreover, the authors do not report anything on intraand interobserver variability of these assessments that probably would also hamper the use of this instrument. They published a small validation substudy a few years ago focusing on interobserver variability of shoulder and hip pathologies, but only 2 PMR and 2 rheumatoid arthritis patients were compared (3). It is important to emphasize that these proposed criteria are provisional (meaning that they must ultimately be confirmed in additional prospective validation cohorts) and not diagnostic criteria. Classification criteria are useful for defining patient groups for clinical or epidemiologic studies. They are not developed or intended to define diagnoses in clinical practice. This point seems particularly relevant in PMR, a syndrome that is common, eminently treatable, and most often initially encountered by and treated by primary care providers This editorial is published simultaneously in the April 2012 issue of Annals of the Rheumatic Diseases. Robert Spiera, MD: Hospital for Special Surgery, New York, New York; René Westhovens, MD, PhD: Katholieke Universiteit Leuven, Leuven, Belgium. Address correspondence to René Westhovens, MD, PhD, Department of Rheumatology, University Hospital Katholieke Universiteit Leuven, Leuven 3000, Belgium. E-mail: rene.westhovens@ uzleuven.be. Submitted for publication November 30, 2011; accepted in revised form January 8, 2012.