The relationship between post-concussion syndrome (PCS) and psychological symptoms is complex, and some claim that pre-existing psychological issues influence or even determine the outcome of PCS.
This study evaluated if depression influenced the persistence of symptoms following mild traumatic brain injury. At least three months following injury, 20 post-concussive patients who had been clinically diagnosed with depression in the preceding three years were compared to a non-depressed sample. The researchers measured neuropsychological functioning—forgetfulness, concentration, fatigue and decision-making abilities—as well as post-concussive symptoms—dizziness, visual disturbance, appetite change, and nausea.
There were no significant differences between the depressed and non-depressed groups:
"The assumption that pre-existing affective disorder (particularly a remote history of depression) can account for the post-concussive complaints or neuropsychological deficits of patients with persistent symptoms after a cerebral concussion does not appear warranted based on the present investigation. The patients with a history of depression did not exhibit greater severity of self-reported post-concussive of emotional symptoms. It therefore appears unlikely that these patients' subjective complaints could be attributed solely to premorbid depression."
Cicerone KD, Kalmar K. Does premorbid depression influence post-concussive symptoms and neuropsychological functioning? Brain Injury 1997;11(9):643-648.