Abstract and Introduction
Study Design: A longitudinal cotwin control study of the Vietnam Era Twin Registry.
Objective: The aim of this study was to examine the association of post-traumatic stress disorder (PTSD) symptoms with incident chronic back pain (CBP), while controlling for genetic factors and early family environment.
Summary of Background Data: It is unknown whether PTSD symptoms are associated with an increased incidence of CBP.
Methods: In 2010 to 2012, a baseline survey was undertaken as part of a large-scale study of PTSD. Study participants completed the PTSD Symptom Checklist (PCL) and a self-report measure of CBP. In 2015 to 2017, a follow-up survey was sent to all 171 monozygotic (MZ) twin pairs (342 individuals) where both cotwins had no history of CBP at baseline, but only one cotwin in the pair met criteria for having current PTSD symptoms (one twin with PCL <30 and the cotwin with PCL ≥30). No other inclusion/exclusion criteria were applied. CBP at 5-year follow-up was defined as back pain of duration ≥3 months in the low back or mid/upper back. Covariates included age, race, education, income, Veterans Affairs health care use, disability compensation, smoking, body mass index, and depression. Statistical analysis estimated the cumulative incidence of CBP according to baseline PTSD symptoms. Risk ratios (RRs) and 95% confidence intervals (95% CIs) were estimated in matched-pair cotwin control analyses adjusting for familial factors.
Results: Among 227 males completing 5-year follow-up, including 91 MZ twin pairs, the mean age was 62 years. Five-year incidence of CBP in those without and with baseline PTSD symptoms was 40% and 60%, respectively. Baseline PTSD symptoms were significantly associated with incident CBP in crude and multivariable-adjusted within-pair analyses (RR 1.6, 95% CI 1.2–2.1; P = 0.002).
Conclusion: PTSD symptoms were associated with an increased incidence of CBP, without confounding by genetic factors or early family environment. PTSD symptoms may be a modifiable risk factor for prevention of CBP.
Level of Evidence: 3
Back pain is one of the most common symptoms prompting health care visits and the leading cause of years lived with disability worldwide.[1,2] Mental health conditions may predispose to incident back pain,[3,4] and the comorbidity of back pain with mental health conditions predicts worse overall back-related outcomes.[5–8] Although the association of back pain with depression and anxiety has been extensively studied, less is known regarding the relationship between back pain and other mental health conditions, such as post-traumatic stress disorder (PTSD).
Military Veterans have a high prevalence of both PTSD and back pain.[9,10] PTSD is comorbid with chronic pain in 47% to 59% of United States (US) military Veterans in outpatient pain clinics and post-deployment clinics,[11,12] where the back is the most common individual location of chronic musculoskeletal pain. Much remains unknown about the relationship between PTSD and back pain. The association between PTSD and back pain may be due to causal links between these two conditions or their correlates, raising the possibility that treatment of one condition might prevent or improve symptoms of the other. Alternatively, PTSD and back pain may be explained by other confounding factors. Several theoretical models to explain the comorbidity of PTSD and chronic pain have suggested that the two conditions coexist due to underlying "vulnerabilities" that predispose to the development or maintenance of both conditions.[13–15] Such vulnerabilities might be genetic predispositions or familial factors related to upbringing that lead to both PTSD and back pain, without a direct causal link between the two conditions. If such predispositions are a major driver of the PTSD-back pain association, treatment of PTSD symptoms would not be expected to have a direct effect on the occurrence of back pain. Twin studies of back pain indicate a heritability of 40%,[16,17] with generally greater heritability for chronic back pain (CBP) than for any back pain, and PTSD is also moderately heritable (up to 46%[19,20]). These estimates suggest that shared genetic contributions to CBP and PTSD are a possible explanation for their co-occurrence, as seen in prior twin studies of depression/anxiety and CBP.[21–23] However, to date, no published studies have used genetically informative samples that permit the examination of whether PTSD symptoms are a risk factor for future CBP independent of genetic factors and the early family environment.
The aim of the current study was to examine whether PTSD is associated with an increased risk of CBP at 5-year follow-up, after accounting for confounding by genetic or early family environmental influences (which henceforth we refer to collectively as "familial factors").
Spine. 2019;44(17):1220-1227. © 2019 Lippincott Williams & Wilkins