Income dynamics and risk of complex regional pain syndrome: a nationwide cohort study

Complex regional pain syndrome (CRPS) is a chronic, treatment-refractory neuropathic disorder associated with substantial functional impairment and socioeconomic burden. Although socioeconomic conditions have been implicated in vulnerability to chronic pain, evidence on the association between income dynamics and the risk of developing CRPS remains limited. Using the Korean National Health Insurance Service database, we conducted a nationwide cohort study including 3,437,021 adults in South Korea who underwent national health screening in 2012 and were followed through to 2022. Income-related indicators-including baseline income level, cumulative income exposure, income change, and income volatility during the 5 years preceding baseline-were assessed. Incident CRPS was identified using Korean Standard Classification of Diseases codes combined with registration in the Rare Intractable Disease program. Compared with the highest income quartile, individuals in the lowest income quartile had a higher CRPS risk (adjusted hazard ratio [aHR], 3.74; 95% confidence interval [CI], 3.07-4.56). Risk increased with longer duration of low-income status (aHR, 1.91; 95% CI, 1.48-2.45 for 5 vs 0 years) and decreased with longer duration of high-income status (aHR, 0.55; 95% CI, 0.44-0.70 for 5 vs 0 years). In addition, high-income volatility (highest vs lowest quartile aHR, 1.48; 95% CI, 1.23-1.78) and downward income changes (peak aHR, 1.84; 95% CI, 1.24-2.73) were independently associated with increased CRPS risk. These findings suggest that income dynamics represent an important socioeconomic risk factor for CRPS and highlight the relevance of longitudinal socioeconomic vulnerability in the development of disabling chronic pain conditions.