Assessing the Association Between Child Maltreatment and Chronic Widespread Pain Adjusting for Familial Confounding: A Co-Twin Control Approach

Many studies document the relationship between child maltreatment (CM) and increased risk of chronic pain. However, estimating the effect of CM on chronic pain is challenging given the threat of familial and other environmental confounding. We used a co-twin control approach to examine the potential causal relationship between self-reported CM (i.e., experiencing any emotional, physical, or sexual abuse, physical neglect, or witnessing family violence) and self-reported chronic widespread pain (CWP) symptom counts after ruling out familial confounding by design. We applied a complete case approach to cross-sectional, national Swedish data from the Study of Twin Adults: Genes and Environment (N = 6,936 individuals in complete twin pairs; Mage = 32.9; SDage = 7.7; 60.5% female). Negative binomial generalized estimating equation models examined unrelated-individual and within-twin-pair associations between CM and CWP. Adjusting for age and biological sex, CM was associated with increased rates of CWP symptoms among unrelated individuals (incidence rate ratio [IRR], 2.35 [95% CI: 2.02, 2.74]). In the within-twin-pair comparison, which provided a stronger test of a causal effect independent of familial confounding, the association attenuated only slightly (IRR, 1.74 [1.36, 2.22]). That is, twins who experienced CM were expected to have relatively greater CWP symptoms than their co-twins who did not experience CM. Restricting the sample to monozygotic twins to further rule out genetic confounding produced similar results (IRR, 1.87 [1.29, 2.70]). Findings preliminarily support the hypothesis that CM is an important risk factor of CWP. Future directions include statistically accounting for missing data to further examine causality.