Adverse outcomes of chronic widespread pain and common mental disorders in individuals with sickness absence – a prospective study of Swedish twins

BACKGROUND: Chronic widespread pain (CWP) and common mental disorders (CMDs) are common public health problems, but little is known about the role of CWP and CMDs on future adverse outcomes among work disabled individuals. The aims of the study were to investigate the associations between CWP and CMDs with subsequent disability pension (DP), long-term unemployment (> 90 days) and all-cause mortality in individuals with sickness absence (SA) and whether the associations were explained by familial factors. METHODS: In this prospective cohort study, 7884 Swedish twins born between 1933 and 1985 were included and baseline data were gathered from a questionnaire in 1998 to 2006. Register data were used for obtaining information regarding demographics, SA, DP, unemployment and mortality. Cox proportional hazards regressions were used to calculate Hazard Ratios (HR) with 95% Confidence Intervals (CI) for the associations between CWP and/or CMDs with DP, unemployment and mortality, while conditional Cox models for twin pairs provided control for familial confounding. RESULTS: Having either CWP or CMDs among those with a history of SA was associated with a higher risk of DP and all-cause mortality than individuals without CWP and CMDs after controlling for socio-demographic and health factors. Moreover, sick-listed individuals with both CWP and CMDs had a higher risk of DP while those who only had CMDs had a higher risk of long-term unemployment compared to those without CWP and CMDs. The association between CMDs with DP and long-term unemployment was no longer significant when controlling for familial factors. CONCLUSIONS: CMDs was a risk factor for DP, unemployment and mortality among individuals with SA, while CWP seems to be important in relation to future DP and mortality. Familial factors played a role in the associations between CMDs and DP and CMDs and unemployment.