Abstract and Introduction
This review identified prospective cohort studies in the general population, which showed incidence (23 papers) and risk factors (37 papers) for fibromyalgia and chronic widespread pain. Median incidence of physician diagnosed fibromyalgia in the general population was 4.3 per 1000 person-years (range = 0.33–18.8) but 14.0 (1.2–32.7) if medical illness was present. Median incidence of chronic widespread pain was 12.5 per 1000 person-years (7.2–81.6) but 67 per 1000 person years (14.8–124) for those with pre-existing pain. Risk factors included various childhood difficulties, female sex (except with pre-existing medical disorders), older/middle age, smoking, high body mass index, alcohol abstinence, and pre-existing medical disorders in adulthood. The strongest associations were with sleep disorders, headaches and other pains, depression, and illness behaviour. These data suggest strongly that there are many aetiological routes into fibromyalgia, and future research could be enhanced by studying the underlying mechanisms relating to these risk factors.
Fibromyalgia is a common condition, but its aetiology is not fully understood.[15,21,41,43] Previous reviews have listed numerous somatic, psychological, and social factors associated with fibromyalgia in cross-sectional studies, but very few large prospective studies have been reported.[4,10,15,21] As a result, too many reviews rely on prevalence data to support aetiological theories when only prospective studies can demonstrate causality.
There are several definitions of fibromyalgia, and the prevalence varies between 1.2% and 5.4% of the population according to definition. Chronic widespread pain (CWP) is more common affecting 14.2% of UK population.[9,18] The incidence of fibromyalgia has been measured rarely and is quoted in reviews as 5.83 per 1000 using ACR criteria in middle-aged women, and 11.28 and 6.88 per 1000 in female and male adults, respectively, using ICD-9 codes.[4,39] The Forseth study found the incidence of CWP to be approximately twice that of fibromyalgia. The current review included studies of fibromyalgia and CWP; the incidence data are presented separately, but the risk factors have been assessed together partly to maximise numbers of studies.
There has been no previous systematic review of onset of fibromyalgia in population-based samples. One systematic review concerned physical and psychological traumatic events in fibromyalgia development, but the only prospective studies concerned follow-up of people with whiplash or other injuries. Another review reported an increased prevalence of fibromyalgia in patients with other medical disorders including irritable bowel syndrome, diabetes, and patients undergoing haemodialysis. A review concerning the transformation of regional pain to CWP was inconclusive, possibly because it included very few studies. A further systematic review found a bidirectional relationship between sleep disturbance and CWP. This review aimed to find all studies that demonstrated the incidence of fibromyalgia and CWP in population-based cohorts of adults and collate the risk factors for new onsets of both conditions.
Pain. 2020;161(6):1169-1176. © 2020 Lippincott Williams & Wilkins