Evolving concepts in the classification, diagnosis and epidemiology of fibromyalgia

Marco Di Carlo
Rheumatological Clinic, Università Politecnica delle Marche, Ospedale “Carlo Urbani”, Jesi (Ancona), Italy

Different studies, coming from different countries and settings estimated the prevalence of fibromyalgia (FM). The worldwide prevalence of FM is around the 2.7%, ranging from values of 0.4% (Greece) to 12%  (Tunisia). Across the various continents, the prevalence of FM is of the 3.1 % in the Americas, 2.5 %in Europe, and 1.7 % in Asia. Globally, FM mean prevalence is 4.2 % in females and 1.4 % in men, with a female-to-male ratio of 3:1. The prevalence of the disease is also influenced by the diagnostic criteria adopted: applying the 2010 criteria of the American College of Rheumatology (ACR) seems to be higher than the 1990 criteria that required the objective examination of the tender points. Some studies have also evaluated the incidence of the disease. A Norwegian study shows an incidence of 5.83 cases/1000 people in women between 20 and 49 years of age, while Weir and coworkers  detected an age-adjusted incidence rate of 6.88 cases/1000 person-years for males and 11.28 cases/1000 person-years for females. Over the last decades, numerous efforts have been made to establish valid diagnostic/classification criteria for FM, and this area of research is still extremely dynamic. FM is still a complex disease to diagnose, and the diagnostic delay is about two years. As a result, FM is still an under-diagnosed and under-treated disease. The 1990 ACR criteria were extremely focused on chronic widespread pain (CWP) (defined as pain in the left side of the body, pain in the right side of the body, pain above the waist, pain below the waist, and axial skeletal pain) and tenderness (defined as pain on palpation of 11 or more of 18 specific tender point sites on the body), with little relevance to symptoms for diagnostic purposes. Therefore, for over 20 years, a history of CWP and the presence of tender points have been the cornerstones for the diagnosis of FM. However, over the years a number of critical issues have emerged with regard to this diagnostic/classification approach. First of all, it has been revealed that in primary care many physicians do not know how to evaluate tender points and, refusing to do so, in practice the diagnosis is based on symptoms. Secondly, the literature has increasingly valued the presence of symptoms, such as fatigue, unrefreshing sleep, and cognitive symptoms, as key elements for the diagnosis of FM. A third important objection was that a complex pathology such as FM is that characterized by manifestations that are a continuum, whose diagnosis is difficult to interpret in a simple cut-off point. Consequently, the 2010/2011 criteria have been developed with the intention of enhancing the non-tender point symptoms by translating them into a symptom severity (SS) scale. In addition, the formal count of tender points was replaced by the widespread pain index (WPI), avoiding the objective examination. Recently, one of the criticisms levelled against the 2010/2011 ACR criteria, is that they have allegedly moved away from chronic pain. The latest development of diagnostic criteria for FM has been provided by the FM Working Group of the AAPT (Analgesic, Anesthetic, and Addiction Clinical Trial Translations Innovations Opportunities and Networks [ACTTION] - American Pain Society [APS] – Pain Taxonomy). In these criteria, FM has again been classified as a disease characterised predominantly by chronic pain (a self-reported of the multi-site pain [MSP], defined by the presence of at least six of nine pain sites throughout the body), along with fatigue and sleep problems as two key associated symptoms.

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