Effect of depression on cognition after mild traumatic brain injury in adults.

Objective: The current study examined the effect of depression on cognitive test performance in a sample of adults seeking treatment for a mild traumatic brain injury (MTBI). We hypothesized that patients with greater depressive symptoms would perform worse on tasks of fluid cognition compared to those without depression, after controlling for potential confounds.

Method: Patients (N = 76) completed a brief cognitive test battery (NIH Toolbox Cognition Battery; NIHTB-CB) and a depression screening questionnaire (PHQ-9) at 11.7-weeks post injury (SD = 6.3 range 2-26). Cognitive scores were adjusted for age, education, gender, and race/ethnicity. Depressive symptoms were examined continuously and dichotomized as: (1) total PHQ-9 score of ≥ 10, the optimal cut-off for Major Depressive Disorder caseness from prior research, and (2) five or more symptoms of depression, including either depressed mood or anhedonia (i.e. DSM-5-based definition).

Results: Twenty-seven patients (35.5%) met DSM-5-based criteria for depression and 42 (55.3%) met criteria based on PHQ-9 > 10. Depression symptom severity correlated with lower fluid cognition composite scores [r = -.22, p = .05] and contributed to the prediction of fluid cognition performance in a model that controlled for time since injury and crystallized cognitive abilities [F(3, 72) = 7.49, p < .001; R = 20.6%]. Examining specific NIHTB-CB fluid subtests, the largest group differences were seen on processing speed (d = .40-.49), cognitive flexibility (d = .32-.36), and episodic memory (d = .20-.34). Depression severity was strongly associated with overall post-concussion symptom burden (r = .77, p < .001).

Conclusion: Depression is a common comorbidity and an important factor to consider when interpreting neurocognitive test performance in adults with concussion in a clinical setting.