Reverse Causality in the Association Between Whiplash and Symptoms of Anxiety and Depression

Abstract

Longitudinal population-based cohort study. The aim of this study was to examine the possibility of reverse causality, that is, if symptoms of anxiety and depression are associated with incident self-reported whiplash injury. The clinical relevance of self-reported whiplash injury was evaluated by its association with subsequent disability pension award. Whiplash is associated with an increased level of anxiety and depressive symptoms. This increase in psychological distress is generally understood as the consequence of the accident and related whiplash. Longitudinal data from the HUNT study was used. Baseline measures of symptoms of anxiety and depression were used in prediction of incident whiplash injury self-reported at follow-up 11 years later. Incident disability pension award was obtained from a comprehensive national registry during 2-year follow-up after self-reported whiplash injury. Case-level symptom load of anxiety and depression at baseline increased the likelihood of reporting incident whiplash at follow-up (odds ratio [OR] = 1.60, 95% confidence interval = 1.22-2.11). Self-reported whiplash increased the chances of a subsequent disability pension award (OR = 6.54), even in the absence of neck pain (OR = 3.48). This is the first published study with a prewhiplash prospective evaluation of psychological status. Our findings are in conflict with previous research suggesting whiplash to be the cause of associated psychological symptoms rather than their consequence. Self-reported whiplash injury was clinically relevant as it independently increased subsequent disability pension award. The strength of this effect, even in the absence of neck pain, suggests the ascertainment of this diagnostic label, or factors associated with this, are important predictors of disability.