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New Criteria Would Double Fibromyalgia Cases
Monday 9 February 2015
New Criteria Would Double Fibromyalgia Cases
More than 5% of the general population could be diagnosed under new system.
Applying the proposed 2010 modified American College of Rheumatology (ACR) fibromyalgia classification criteria greatly expands the number of persons who qualify for the diagnosis compared with earlier ACR criteria. More than 5% of the general population fulfill the modified 2010 criteria, compared with less than 2% who fulfilled the 1990 and the proposed 2010 criteria, report researchers in Arthritis and Rheumatology.
The findings "do not support previous claims that the modified 2010 criteria do not result in inflated prevalence estimates," they concluded. "We have demonstrated that the prevalence of fibromyalgia varies more than four-fold with the application of different ACR fibromyalgia classification criteria sets, the lowest estimate being with the 2010 criteria and the highest with the modified 2010 criteria. Further, we have shown that there are fundamental differences in the populations identified, in terms of sex ratio and preexisting comorbid rheumatologic conditions."
The modified 2010 classification criteria rely on self-reported pain and a simplified self-reported version of somatic symptoms, whereas previous ACR classification criteria required moderate or high levels of chronic pain using clinical judgment. A large population survey in Germany found a prevalence of fibromyalgia of 2.1% using the modified 2010 criteria.
Investigators led by Gareth T. Jones, PhD, at the University of Aberdeen in Scotland, compared three sets of fibromyalgia classification criteria -- the ACR 1990 criteria, the ACR 2010 criteria, and the ACR modified 2010 criteria -- in a general population sample of adults in northeast Scotland. Among 1,604 respondents to screening questionnaires that asked about pain, symptoms, and rheumatologic diagnoses, 104 of 269 who reported chronic widespread pain per the ACR 1990 criteria or fibromyalgia according to the ACR modified 2010 criteria accepted an invitation to attend a research clinic for a clinical examination.
Of the 104 clinic attendees, 32 (31%) met at least one set of criteria for fibromyalgia. Eleven met the ACR 1990 criteria, seven met the ACR 2010 criteria and 27 met the ACR modified 2010 criteria. Overlap was modest, with only four subjects (12.5%) meeting all three sets of criteria.
The prevalence of fibromyalgia was 1.7% according to ACR 1990 criteria, 1.2% according to ACR 2010 criteria and 5.4% according to the ACR modified 2010 criteria.
Those meeting the ACR 1990 criteria were mostly female, with a female to male ratio of 13.7 to 1. The female to male ratio was lower when using the ACR 2010 criteria (4.8 to 1) and lower still when using the ACR modified 2010 criteria (2.3 to 1).
A total of 55% who met the ACR 1990 criteria reported prior rheumatologic diagnoses, compared with 28% who met the ACR 2010 criteria and 45% who met the ACR modified 210 criteria. All who fulfilled both the ACR 2010 and the ACR modified 2010 criteria met the ACR modified 2010 criteria on the basis of a high score on the Widespread Pain Index rather than the Symptom Severity Scale.
The specificity of the ACR 2010 criteria was "near perfect," with 92 of 93 participants correctly identified from these criteria as not having fibromyalgia, the authors note. The sensitivity, however, was barely more than 50%. "The modified 2010 criteria, while exhibiting improved sensitivity (more participants positive for fibromyalgia according to the 1990 criteria were correctly identified), suffered from a decrease in specificity (fewer participants negative for fibromyalgia according to the 1990 criteria were correctly identified)," they wrote.
Before confirming the new criteria, the authors urge the ACR to consider that the new set of criteria identifies a different patient group compared with the ACR 1990 criteria, with the modified 2010 criteria influenced more by somatic symptoms rather than pain, and that "operationalization of any new criteria must be clear and unambiguous, as well as immediately implementable." They state that, "This is not currently the case."
A limitation is the modest (36%) response rate to the initial survey and the reliance on very small samples to determine prevalence. Another limitation was the use of a single clinician for the examination and case history.
The study was supported by the University of Aberdeen Development Trust from charitable donations for research in the study of fibromyalgia.
The above originally appeared here.
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