Nightmare Disorder and Low Back Pain in Veterans: Cross-Sectional Association and Effect Over Time

Abstract Low back pain (LBP) disproportionately impacts U.S. military veterans compared to non-veterans. Although the effect of psychological conditions on LBP is regularly studied, there is little published to date investigating nightmare disorder (NMD) and LBP. The purpose of this study was to (1) investigate whether an association exists between NMD and LBP and (2) estimate the effect of NMD diagnosis on time to LBP. We used a retrospective cohort design with oversampling of those with NMD from the Veterans Health Administration (n=15,983). We used logistic regression to assess for a cross-sectional association between NMD and LBP and survival analysis to estimate the effect of NMD on time to LBP, up to 60-month follow-up, conditioning on age, sex, race, index year, Charlson Comorbidity Index, depression, anxiety, insomnia, combat exposure, and prisoner of war history to address confounding. Odds ratios (with 95% confidence intervals) indicated a cross-sectional association of 1.35 (1.13–1.60) and 1.21 (1.02–1.42) for NMD and LBP within 6 months and 12 months pre- or post-NMD diagnosis, respectively. Hazard ratios (HR) indicated an effect of NMD on time to LBP that was time-dependent – HR (with 95% confidence intervals) 1.27 (1.02–1.59), 1.23 (1.03–1.48), 1.19 (1.01–1.40), and 1.10 (0.94–1.29) in the first 3, 6, 9, and 12 months post-diagnosis, respectively – approximating the null (1.00) at >12 months. The estimated effect of NMD on LBP suggests improved screening for NMD among veterans may help clinicians and researchers predict (or intervene to reduce) risk of future back pain.