Fibromyalgia criteria in a tertiary pain clinic

In this issue of the Journal, Egloff and colleagues (1) describe a meticulously performed 15-month, 300patient study of the American College of Rheumatology (ACR) 1990 and 2010 preliminary criteria for fibromyalgia (FM) in patients with ‘functional pain syndromes’, that is syndromes that by definition do not often have widespread or four-quadrant pain, one of the 1990 criteria (2, 3). In the study by Egloff et al, 8.3% of their patients met the ACR 1990 criteria and 43.3% met the 2010 criteria. The specificity of the 2010 criteria for the 1990 diagnosis was 60%, a value that is the smallest of the eight studies that have considered this issue and that had a mean specificity of 88.5% (Wolfe, unpublished observations). In addition, less than half of all 2010 positive patients (46%) suffered from pain in all four quadrants and many had limited forms of pain disorders. To understand Egloff et al’s data, we must first recognize that their population is special. It is composed entirely of hospitalized functional pain syndrome patients and resides in ‘a tertiary university centre for multimodal pain therapy’, where there is an excess of such pain syndromes. The authors raise many important issues that they summarize by stating: ‘By omitting the requirement of “generalized pain”, the distinction between the FM and more localized functional pain syndromes is blurred. Furthermore, by dropping the tender point assessment, the ACR 2010 criteria omit examination of the distinctive “hyperalgesia aspect” of FM. ’ We define FM as a syndrome characterized by generalized pain, decreased pain threshold, and multiple symptoms, in particular non-restorative sleep, fatigue, cognitive problems, and multiple somatic symptoms. There is no gold standard for FM. All criteria for diagnosis are inherently approximate and probabilistic, as patient heterogeneity, variability of symptoms, and measurement errors render it impossible to define criteria for FM that perfectly or almost perfectly identify all cases and noncases. In the 1990 criteria study, the presence of ≥ 11 tender points led to correct classification in 84.2% of cases, using as the gold standard the opinion of the physicians participating in the study (a committee) (2). When the widespread pain criterion was added, the percentage increased to 84.9%. Widespread pain was added to the 1990 criteria to reduce the researchers’ burden by eliminating the need for all subjects to have the tender point examination. That is, if a patient had ≥ 11 tender points, they almost always had widespread pain. The authors of the ACR 2010 and the modified 2011 criteria were very aware that FM should be considered a disorder of generalized pain (3). In fact, they wrote: ‘Among patients positive for the modified ACR 2010 criteria, 93.7% satisfied the widespread pain criterion’. We did not include an absolute widespread pain criterion because all of the authors had observed patients who did not quite have widespread pain but had all of the other features of the syndrome. In the National Data Bank for Rheumatic Diseases (NDB) (4), we regularly observe widespread pain in FM-positive patients at levels in excess of 93% (5). In a German population study, the widespread pain rate was 83% (6). It seems likely that Egloff et al did not find high levels of widespread pain because of the nature of their population and sample. Of note, the ratio of the 2010 symptom severity score (SSS) to the widespread pain index (WPI) in the Egloff et al study was 1.1 compared to 0.7 in the eight-criteria studies cited earlier (Wolfe, unpublished observations). This suggests that patients in this study had proportionately less pain but more symptom severity than in other published reports. In making general rules in criteria, we acknowledge that such rules might not work as well at the extremes and in subsetted specialty samples. In dropping the tender point count in favour of the WPI, we noted in the ACR 2010 study that tender points correlated with the WPI at r = 0.773, and that by regression analysis a 1-unit increase in WPI led to a 1.0 [95% confidence interval (CI) 0.9–1.1]-unit increase in tender point count. The tender point count was dropped in the 2010 criteria because few physicians carried out the examination and often blundered in its performance; Frederick Wolfe, National Data Bank for Rheumatic Diseases, 1035 N. Emporia, Ste 288, Wichita, KS 67214, USA. E-mail: fwolfe@arthritis-research.org