A Twin Study of the Association Between PTSD Symptoms and Rheumatoid Arthritis

Objectives: To assess the association between posttraumatic stress disorder (PTSD) and rheumatoid arthritis (RA) and to determine if this was due to PTSD or confounding by environmental and genetic factors. Methods: Data were obtained from 3143 twin pairs in the Vietnam Era Twin Registry, which included male twin pairs who served during the Vietnam War era (mean age, 40.6 years; standard deviation, 2.9). Measurements included a PTSD symptom scale, history of physician-diagnosed RA, sociodemographics, and health confounding factors. Co-twin control analytic methods used generalized estimating equation logistic regression to account for the paired twin data and to examine the association between PTSD symptoms and RA in all twins. Separate analyses were conducted within twin pairs. Results: The prevalence of RA among this population was 1.9% (95% confidence interval, 1.6-2.3) and the mean PTSD symptom level was 25.5 (standard deviation, 9.6). PTSD symptoms were associated with an increased likelihood of adult RA even after adjustment for confounding (p(trend) < .001). Among all twins, those in the highest PTSD symptom quartile were 3.8 times more likely (95% confidence interval, 2.1-6.1) to have RA compared with those in the lowest. These findings also persist when examined within twin pairs (p(trend) < .022). Conclusions: PTSD symptoms were associated with adult RA onset. Even after adjustment for familial/genetic factors and other confounders, an association between PTSD symptoms and RA remained. This is one of the first studies to demonstrate a link between PTSD and RA onset among a community-based population sample, independent of familial and genetic factors.