“Classification, Epidemiology and Natural History of Fibromyalgia”
Musculoskeletal (MSK) pain is common worldwide. In economically developed countries such as the USA, between 14 and 26% of the adult population suffers from chronic pain or arthritis,i, approximately 11% report chronic, widespread painii and MSK disorders account for 15% of work loss daysiii. The figures are similar elsewhere. In Canada, 15% of adults report chronic MSK painiv, 7% reported chronic, widespread painv and 5% report physical disabilities secondary to MSK illness.vi In Europe, the prevalence of chronic widespread MSK pain varies between 11 and 17%vii,, and MSK disorders account for between 14 and 17% of work loss days.viii In economically developing countries, the prevalence of MSK pain may be even higher, effecting 24-31% of adults in Indonesiaix and 36% of respondents in Thailand.x
Fibromyalgia Syndrome (FMS), also known as fibrositis, is a common form of non-articular rheumatism that is associated with chronic generalized MSK pain, fatigue, and a long list of other complaints.xi Clinic studies have found FM to be common in countries worldwide, including economically developing countries such as Mexico,xii Polandxiii and Pakistan.xiv The primary objective of this article is to review the classification, epidemiology and natural history of FM.
The Classification of Fibromyalgia
Controversies in Classification
Medicine has recognized muscular and other soft tissue pain as clinical problems for several centuries.xv, Gowers coined the term “Fibrositis” in 1904 for a painful condition of muscles, which he believed to be due to inflammation.xvi Although clinical states of regional, and generalized muscular pain attracted the interest of some physicians, no consistent pathological changes could be detected, certainly none that strongly suggested inflammation. “Fibrositis” had become an almost forgotten entity until Smythe and Moldofsky started publishing their studies.xvii The term “fibrositis” was subsequently changed to that of “fibromyalgia” (FM) or “fibromyalgia syndrome” (FMS) as it became clear that inflammation in either muscle or fibrous tissue was not part of this condition.xviii
At first FM seemed to meet with a friendly reception. Physicians were pleased to find that they could now label the many patients with generalized pain, fatigue, and sleep disorders that they were seeing in their practices. This honeymoon period did not last very long. The last ten years especially have seen increasingly hostile criticism of FM. The condition affects many patients, and a veritable epidemic was said to have occurred; moreover, many of the sufferers seemed unable to work and requested disability payments.xix FM was perceived by some as one of several functional somatic syndromes with patients mistakenly attributing abnormalities of function to a physical rather than psychological condition.xx There are also those who think that FM does not exist.xxi Some of the criticism probably reflects a sense of frustration with the slow progress made in the understanding and treatment of this condition, the absence of specific abnormalities, and the difficulties in assessing disability claims made by the patients.xxii
Frustrations aside, there are nevertheless some strong criticisms, which have to be addressed. Three of these are especially important [see Table 1]:
is it appropriate to consider FM as an entity that deserves specific recognition and is distinct from chronic widespread pain, (CWP)?
the definition of FM by a committee of the American College of Rheumatology (ACR) (4) involved tautological reasoning, and no gold standards were used;xxiii
both the historical criteria (pain) and the physical signs (report of pain on pressure of tender points) are entirely subjective and patient-dependent without any hard evidence of underlying abnormalities. What objective changes, if any, are there to support the existence of FM?
A distinct entity or part of a spectrum?
Generalized musculoskeletal pain, which accounts for the great majority of cases of
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