Studies of the relation of fibromyalgia (FM) and widespread pain (WSP) to mortality have differed as to the presence or absence of an association and the extent of cause-specific mortality. However, no studies have investigated which definitions of FM and WSP associate with mortality, nor of FM mortality in other diseases. We investigated these issues and the meaning of mortality in patients with FM.
We used Cox regression to study 35,248 rheumatic disease patients with up to 16 years of mortality follow-up in all patients and separately in those with diagnoses of rheumatoid arthritis (RA) (N = 26,458), non-inflammatory rheumatic disorders (NIRMD) (N = 5,167) and clinically diagnosed FM (N = 3,659). We applied 2016 FM criteria and other FM and WSP criteria to models adjusted for age and sex as well as to models that included a full range of covariates, including comorbid disease and functional status. We estimated the degree of explained of variance (R2) as a measure of predictive ability.
We found positive associations between al`l definitions of FM and WSP and all-cause mortality, with relative risks (RR)s ranging from 1.19 (95%CI 1.15-1.24) for American College of Rheumatology (ACR) 1990 WSP to 1.38 (1.31-1.46) in age and sex adjusted revised 2016 criteria (FM 2016). However, in full covariate models the FM 2016 RR reduced further to 1.15 (1.09-1.22). The association with mortality was noted with RA (1.52 (1.43-1.61)), NIRMD (1.43 (1.24-1.66)) and clinical FM (1.41 (1.14-1.75) - where 37% of FM diagnosed patients did not satisfy FM 2016 criteria. In the all-patient analyses, the age and sex explained variation (R2) was 0.255, increasing to 0.264 (4.4%) when FM 2016 criteria were added, and to 0.378 in a full covariate model. Death causes related to FM 2016 status included accidents, 1.45 (1.11-1.91); diabetes 1.78 (1.16-2,71); suicide, 3.01 (1.55-5.84) and hypertensive related disorders, 3.01 (1.55-5.84). Cancer deaths were less common 0.77 (0.68-0.88).
FM is weakly associated with mortality within all criteria definitions of FM and WSP examined (3.4% of explained variance), and across all diseases (RA, NIRMD, clinical FM) equally. Clinical and criteria-defined FM had different mortality outcomes. We found no evidence for a positive association of cancer and FM or WSP.