The prevalence of fibromyalgia varied by as much as fourfold, depending on which of three different American College of Rheumatology diagnostic criteria sets was used, a new study reveals.
The findings were published online January 28 in Arthritis & Rheumatology by Gareth T. Jones, PhD, from the University of Aberdeen, United Kingdom, and colleagues.
The investigators compared the 1990 American College of Rheumatology fibromyalgia classification criteria, the 2010 American College of Rheumatology preliminary diagnostic criteria, and the modified 2010 American College of Rheumatology criteria in 104 individuals who had scored positively for possible fibromyalgia on screening questionnaires and were subsequently examined.
The 1990 criteria include a history of chronic widespread pain plus pain on digital palpation in 11 or more of 18 specific sites.
The 2010 provisional classification differed from the 1990 definition by operationalizing the measurement of chronic widespread pain and by eliminating the requirement for a tender point exam, substituting an assessment of fatigue, waking unrefreshed, cognitive symptoms, and somatic symptoms in general. A patient is classified as having fibromyalgia if he or she has high levels of pain plus moderate levels of symptoms or moderate levels of pain plus high levels of symptoms, symptoms present at a similar level for 3 months, and no disorder that would otherwise explain the pain.
In 2011, a modification of the 2010 criteria was proposed that relies on self-reported pain and a simplified self-reported version of somatic symptoms for use in clinical and epidemiologic studies.
Of the 104 study participants, 31% met at least one of the three ACR fibromyalgia criteria: 11 met the 1990 definition, 7 met the 2010 criteria, and 27 met the modified 2010 criteria. There was not a lot of overlap, as only four individuals (12.5%) met all three sets of criteria and only nine (28%) met more than one.
Overall, the prevalence of fibromyalgia was 1.7% (95% confidence interval [CI], 0.7% – 2.8%) with the 1990 criteria, 1.2% (95% CI, 0.3% – 2.1%) with the 2010 criteria, and 5.4% (95% CI, 4.7% – 6.1%) with the modified 2010 criteria. Moreover, the female:male ratios were 13.7:1 for the 1990, 4.8:1 for the 2010, and 2.3:1 for the modified 2010 criteria.
“The current study is the first to compare all 3 sets of classification criteria in a general population sample, and our findings do not support previous claims that the modified 2010 criteria do not result in inflated prevalence estimates,” Dr Jones and colleagues write.
In addition to identifying a greater proportion of men, the modified 2010 criteria also appear to be influenced more by somatic symptoms than by pain, they note.
“Most importantly, operationalization of any new criteria must be clear and unambiguous, as well as immediately implementable. This is not currently the case. Both the ACR 2010 criteria and the ACR modified 2010 criteria are currently considered ‘preliminary,’ and we strongly recommend that the ACR consider these important issues in deciding whether to confirm these proposed criteria for use in future clinical practice and/or research,” they conclude.