The risk factors for self-reported fibromyalgia with and without multiple somatic symptoms: The Lifelines cohort study.

Objective: The numerous risk factors for fibromyalgia reflect its heterogeneous nature. This study assessed whether the predictors of fibromyalgia onset vary according to number of prior somatic symptoms.

Methods: The prospective, population-based Lifelines cohort study included 138,617 adults without fibromyalgia or marked muscle pain. At baseline socio-demographic status, physical and psychiatric disorders, psycho-social and behavioural variables were assessed as potential predictors. At follow-up (mean 2.4 years later) new onsets of fibromyalgia were recorded by self-report. The predictors of new onsets of self-reported fibromyalgia were assessed using logistic regression with interaction terms between key variables and number of somatic symptoms.

Results: At follow-up 679 (0.5%) participants reported new onset fibromyalgia. The strongest predictors were: female sex, rheumatoid and osteo-arthritis, IBS, impaired sleep, migraine, few years of education and impairment by bodily pain. Interaction terms with somatic symptoms were significant for years of education, low income, rheumatoid arthritis and no. of analgesics; these were predictors only for fibromyalgia with few somatic symptoms. Participants with multiple somatic symptoms had a higher number of predictors than those with few somatic symptoms.

Conclusion: This study suggests that people developing self-reported fibromyalgia with multiple pre-existing somatic symptoms have a high risk factor load reflecting risk factors for both fibromyalgia and multiple somatic symptoms. Self-reported fibromyalgia with few somatic symptoms has fewer predictors which may be specific to fibromyalgia. Future research could usefully study whether different pathophysiological mechanisms occur when fibromyalgia is preceded by high or low number of somatic symptoms.