Fibromyalgia Underdiagnosed, Report Mayo Clinic Experts

Janis C. Kelly

December 26, 2012

The first population study to compare the prevalence of diagnosed fibromyalgia (FM) to the general population prevalence of people reporting symptoms that met the updated 2010 American College of Rheumatology (ACR) diagnostic criteria indicates that FM may be more common than previously thought and that most FM cases are not being diagnosed, especially in men.

The researchers, led by Ann Vincent, MD, medical director of the Mayo Clinic's Fibromyalgia and Chronic Fatigue Clinic, Rochester, Minnesota, report, in an article published online November 30 in Arthritis Care & Research, that FM prevalence was 6.4% in the general population of Olmstead County but that the age- and sex-adjusted prevalence of diagnosed FM was only 1.1%.

Age-adjusted FM prevalence in men was 4.88% (95% confidence interval [CI], 2.08 - 7.69) in the general population but only 0.15% (95% CI, 0.12 - 0.19) in the diagnosed cases. Age-adjusted prevalence in women was 7.71% (95% CI, 4.65 - 10.77) in the general population survey and 2.00% (95% CI, 1.8% - 2.12%) in the diagnosed cases. The difference in FM prevalence in women compared with men, adjusted for age, in the general population survey did not reach statistical significance (namely, 4.88 vs 7.71; P = .08). Another surprising finding reported by the researchers was that FM prevalence was somewhat higher in younger age groups (8.45% in those aged 21 - 39 years; 6.02% in those aged 40 - 59 years; and 3.79% in those aged 60 years and older; P = .05 for sex-adjusted differences); these data are "in contrast to the trend of increasing prevalence of diagnosed FM with older age," the authors write

The researchers used data from the Olmsted County, Minnesota, Rochester Epidemiology Project to identify 3410 potential patients with FM to estimate the prevalence of diagnosed FM in clinical practice. They also conducted a random survey of adults in Olmsted County to estimate the percentage who met the FM research survey criteria. Of the 830 participants who responded to the survey, 44, or 5.3%, met the criteria for FM, but only 12 had been diagnosed with FM.

Study Findings Debated by Outside Experts

Dr. Vincent told Medscape Medical News, "This is an epidemiology study, so clinical implications are an extrapolation. However, having said that, the prevalence diagnosed FM (ie, the rate at which FM was being diagnosed in the community) was 1.1%. This is lower than previous estimates of [FM] and suggests that [FM] may be underdiagnosed in the community. Other published literature supports our observation that [FM] is not always recognized or diagnosed correctly when a patient is evaluated."

The researchers were surprised by 2 things from the random survey of the general population: the borderline association of higher prevalence with younger age groups and that FM prevalence in women was not significantly higher than in men. They attribute the former to participation bias. Dr. Vincent said, "This is contrary to what is previously reported and observed and could be related to a low response rate in this [younger age] category, with only sicker people responding."

With regard to prevalence in men, Dr. Vincent said, "The old ACR criteria had some inherent issues (since women are biologically more sensitive to pain, they will have more tender points) and were partly responsible for the big gender difference. The hope of the new criteria was to comprehensively assess presence of [FM] based on all its key symptoms by patient report, and the assumption was that this would correct some of the previously reported gender discrepancy. Our results suggest that this is correct: Men do report symptoms of [FM]. Whether they getting diagnosed is another question."

The ACR diagnostic criteria for FM adopted in 1990 required presence of 11 tender points and led to an estimated FM prevalence of 2% in the US general population, including prevalence of 3.4% in women and 0.5% in men. The 2010 ACR criteria do not require the presence of 11 or more tender points.

Leslie J. Crofford, MD, chief of the Division of Rheumatology and director of the Center for the Advancement of Women's Health at the University of Kentucky, Lexington, who was not involved in the study, discussed the article with Medscape Medical News.

"The 2 studies reported in this paper provide the basis for the next steps in [FM] research, particularly epidemiology. This paper raises the question of whether what you get with different methodologies is the same. Until we go back and look at genetic and physiological factors in patients who are positive for FM, according to the survey criteria, and in patients who have clinically diagnosed FM, we won't know whether they actually have the same disease. Do they have the same genetic changes? Do they have the same changes on functional imaging? We don't yet know the answers to those questions, so we don't know how these 2 methodologies relate to each other."

Mark G. Haviland, PhD, from the Department of Psychiatry at Loma Linda University School of Medicine in California, who has studied FM prevalence in hospitalized patients in the United States, said, "This is a good study and conducted by experienced FM researchers. The study is a good first step in make new estimates based on the new FM diagnostic criteria." Although Dr. Haviland, who was also uninvolved in the trial, found the authors "fair and reasonably complete" in their cautions, interpretations, and limitations noted in the discussion, he said, "It does give me pause that the [male/female] differences are not statistically significant and that there is no increase in FM prevalence as age increases. My understanding is that FM prevalence increases with age up to a point and then declines and that the only issue in dispute is when the decline occurs. To go from the generally accepted 3 to 1 [female] to [male] ratio and to not see an FM [diagnosis] change with age raises questions about the validity of the data."

The study was supported by the National Institute on Aging and the Mayo Clinic Center for Translational Science Activities; the center is funded in part by the National Center for Research Resources. The authors and Dr. Haviland have disclosed no relevant financial relationships. Dr. Crofford is on the editorial board of Arthritis Care & Research, which published the study.

Arthritis Care Res. Published online November 30, 2012. Abstract