How is FM Population Determined?

Have you ever wondered why the reported fibromyalgia population percentages are different?  Between 2-4% of people have fibromyalgia according to oft-cited studies reviewed here.  In the U.S. that difference is 6,337,000 to 12,674,000.

In Wichita, Kansas, (1994) a random sample of 3,006 people in the general population were characterized with no pain (NP), non-widespread pain, and widespread pain.  The prevalence of fibromyalgia was 2%, with occurrence in women 7 times more likely than in men.  Women between 60-79 years had the highest occurrence (>7%).

Wolfe, et al. concluded that "Fibromyalgia is common in the population, and occurs often in older persons.  Characteristic features of fibromyalgia--pain threshold and symptoms--are similar in community and clinic populations, but overall severity, pain, and functional disability are more severe in the clinic population."  (Arthritis Rheum. 1995 Jan;38(1):19-28.)

Weir, et. al evaluated insurance claims (62,000) from 1997 to 2002 using the International Classification of Diseases, 9th Revision to identify fibromyalgia. They reported that females were 1.64 times more likely than males to have FM. (J Clin Rheumatol. 2006 Jun;12(3):124-8.)

Researched in Sao Paulo, Brazil (2009), Assumpcao, et. al found that in an adult, low socioeconomic status population the prevalence of fibromyalgia was 4.4%, similar to other studies in a more diverse socioeconomic population. The authors noted that the "high prevalence of FM found in our study may be explained by the age of our inclusion sample (35-60 years old), when fibromyalgia is more frequent, as shown in studies that enrolled other age categories, such as 18 or 20 and 70 or 80 years old.  Indeed, studies consistently show that FM is more common in middle-aged individuals and is less prevalent in the youngest and the elderly." (BMC Musculoskeletal Disorders 2009,10:64)

Gansky and Plesh assessed the distribution of widespread pain, tender points and fibromyalgia in 1334 young African American and Caucasian women (21-26 years old).  Overall 5.6% reported chronic widespread pain, and 57% of these were confirmed as FM cases.  Caucasian women had significantly more tender points and greater tender point score than African American women.  Overall FM prevalence was 2.4%, with 3% in African American women and 2.0% in Caucasian women. "Increase in body pain and tenderness was significantly associated with decreased subjective socioeconomic status, worse self-reported health, greater impact of premenstrual symptoms on activities, and greater depressive symptoms." They concluded  that "racial differences seem to exist; Caucasian women had significantly increased tenderness while African American women had more widespread pain.  The association of depressive symptoms and pain was stronger in African American women. (J Rheumatol. 2007 Apr;34(4):810-7).

Assessment tools used consistently were the FIQ (Fibromyalgia Impact Questionnaire), the American College of Rheumatology diagnostic criteria for fibromyalgia, Fischer dolorimeter, and pain intensity was measured with the Visual Analogue Scale (VAS).  (The dolorimeter pressure applied to tender points varied with a range from 2.6 kg to 4 kg/cm(2) of pressure.)

It can be concluded that the difference in fibromyalgia population references is based on the population studied.  A conservative figure of 2.5% in the U.S. population would be approximately 8 million people.



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