Assessing the association between child maltreatment and chronic pain: a cross-sectional co-twin control study

Although associations exist between child maltreatment (CM) and multiple chronic painful conditions, it remains unclear to what extent associations might be attributable to unmeasured confounding. We leveraged the co-twin control approach, which rules out genetic and shared environmental confounding by design, with cross-sectional, national Swedish data from the Study of Twin Adults: Genes and Environment (N = 25,418; M age = 33.2; SD age = 7.7; 55.7% female) to assess associations between the number of self-reported experiences of CM (ie, experiencing emotional or physical abuse/neglect, sexual abuse, or witnessing family violence before age 18 years) and self-reported endorsement of criteria for chronic widespread pain (CWP), lower back pain (LBP), and irritable bowel syndrome (IBS). In negative binomial generalized estimating equation models adjusting for age and sex at birth, a one-unit increase in CM counts was associated with 37%, 18%, and 34% more endorsement of CWP, LBP, and IBS criteria, respectively (CWP-adjusted incidence rate ratio [aIRR] = 1.37 [95% confidence interval: 1.32-1.42]; LBP aIRR = 1.18 [1.16-1.21]; IBS aIRR = 1.34 [1.29-1.39]). In comparisons of differentially exposed co-twins, associations attenuated only slightly for CWP (aIRR, 1.21 [1.12-1.31]), LBP (aIRR, 1.15 [1.09-1.21]), and IBS (aIRR, 1.24 [1.14-1.35]). Analyses restricted to monozygotic twins to rule out virtually all genetic confounding produced similar results (CWP aIRR, 1.20 [1.05-1.38]; LBP aIRR, 1.10 [1.01-1.21]; IBS aIRR, 1.14 [1.00-1.30]). Altogether, the results suggest that associations between CM and CWP, LBP, and IBS are not entirely attributable to genetic or shared environmental confounding.