To identify predictors of post-concussion depressive symptoms (PCDS) in patients without baseline depressive symptoms.

Depression is common after concussion and affects quality of life and recovery. To date, the most reliable predictor for development of PCDS is existence of an underlying mood disorder. However, few predictors for PCDS in patients without an underlying mood disorder have been found.

A systematic search was conducted using PubMed for all original articles on post-concussion syndrome in subjects older than 18 years and depression published up to May 2, 2019. Studies that described baseline characteristics for those with and without post-concussion depression were included. Two independent authors reviewed all titles/abstracts to identify studies that met selection criteria. Studies describing pediatric presentation were excluded.

Post-concussion depressive symptoms appear to be associated with symptoms of the concussion itself and with increased number of symptoms reported. Repeat concussions may also increase the risk of developing depressive symptoms. In those with persistent post-concussive symptoms, symptoms seem to appear in a predictable sequence, such that symptoms later in the sequence are more likely to be present if symptoms earlier in the sequence were already present. As such, patients reporting persistent depressive symptoms were more likely to also report existence of correlated cognitive (difficulty concentrating or remembering, feeling dazed) and somatic (headache, fatigue, sensitivity to noise and/or light) symptoms that appear earlier in sequence (OR 2.2).  No association between age and gender and experience of new-onset depressive symptoms following concussion was found.

In patients without underlying depressive symptoms, predictors such as quantity and characterization of post-concussive symptoms may help elucidate patient profiles vulnerable to development of PCDS. Multiple concussions, presence of multiple post-concussive symptoms, and presence of correlated symptoms appear to be predictive. Familiarization with these predictors may lead to earlier detection and optimal treatment of PCDS.