Depression is known to be common psychiatric consequence of head injury. Relationship between head injury and psychosis is less clear.Meta analysis by Molloy et al 2011 found the onset of schizophrenia to be more frequently following head injury. heterogeneity of included studies limited the confidence in that conclusion. Sonja Orlovska et al used the Danish registers to investigate the link between head injury and mental illness .This is the largest study with 34 year follow-up period on this question and authors were able to control for much more confounding factors.
Authors used Danish Civil Registration System , Psychiatric Central Register and the National Hospital Register to examine the link between injury and outcome (schizophrenia spectrum disorders, unipolar depression, bipolar disorder, and organic mental disorders). Onset of all disorders were confirmed to be post injury. Head injury was classified to mild injury ,severe injury and skull fracture. Accident proneness prior to head injury was also measured as accident proneness can be seen as an expression of undiagnosed mental disorder prior to head injury.
113,906 had a hospital contact for head injury between 1977 and 2010 . Of all persons with head injury, a total of 4% were subsequently diagnosed with one of the included severe psychiatric disorders. Of ALL individuals diagnosed with schizophrenia 12% were exposed to head injury, For those with depression, 11% had head injury; among those with bipolar disorder 10% had a previous head injury; and for those with organic mental disorder, 27% had a previous head injury. The incident risk ratio (IRR) was , 1.65, 1.59, 1.28 respectively for schizophrenia, depression, bipolar disorder in other words, 65% increase in the risk of schizophrenia following head injury and risk of depression increased by 59 % and bipolar by 28%.
Highest risk was found during the first year after injury. Head injury between 11 and 15 years of age was the strongest predictor of disorders. The added risk did not differ in those with and without a psychiatric family history. Non CNS fractures ( an indicator of accident proneness) was associated with increase in mental disorders , but the effect was exceeded by the effect of head injury.
Conclusion: Young individuals with head injury are at particularly high risk for serious mental disorders. Understanding of neuroplasticity might shape effective interventions to prevent these outcomes.
Summary of the article:
Orlovska S, Pedersen MS, Benros ME, Mortensen PB, Agerbo E, Nordentoft M.
Am J Psychiatry. 2014 Apr 1;171(4):463-9.