Social factors and pain worsening: a retrospective cohort study

Pain, specifically chronic pain, is a major public health issue worldwide with considerable health-related consequences and large economic impact. The relation between socioeconomic status and pain occurrence is well established. However, little is known on the relation between socioeconomic factors and worsening of pain, including progression from non-chronic pain to chronic pain.

To assess the relation between socioeconomic status and pain worsening, we used the Stockholm Public Health Cohort Study from 2006 to 2014 and analysed data of 9721 participants who completed follow-up. The adjusted incidence rate ratios (IRRs) of moderate and severe pain worsening episodes were computed, using a pain amplification model, which encompasses spreading, somatisation, and psychological distress components. Multiple imputation analysis was performed subsequently to adjust for cohort attrition.

Compared with non-skilled workers, self-employed subjects (IRR=1.18; 95% confidence interval [CI], 1.01-1.39) and non-manual employees were at higher risk of moderate worsening (lower non-manual employees: IRR=1.21; 95% CI, 1.03-1.41; intermediate non-manual employees: IRR=1.26; 95% CI, 1.10-1.44; higher non-manual employees: IRR=1.25; 95% CI, 1.08-1.45). This risk increase was limited to worsening starting at stage 0 (non-chronic pain). No association was found between socioeconomic status and severe pain worsening.

Our results support a moderate association between intermediate and high socioeconomic status, and moderate pain worsening. This association could be explained by the heterogeneous composition of the socioeconomic variable used in this cohort, and by changes in exposure and other time-varying covariables' status during follow-up.