A Danish study of a large cohort of individuals who presented at hospital with head injuries has found that they were at increased risk for later developing schizophrenia, bipolar disorder, depression, and organic mental disorders.
Sustaining a head injury between the ages of 11 and 15 years was the strongest predictor for the subsequent development of schizophrenia, depression, and bipolar disorder.
“Interestingly, it has been theorized that essential neurodevelopment occurs from 11 to 15 years of age, when deterioration in development can possibly lead to psychosis,” write lead researcher Sonja Orlovska (Copenhagen University) and colleagues.
The authors also found that “the effect did not seem to be solely due to accident proneness, and the added risk was not more pronounced in persons with a psychiatric family history.”
The study, published in The American Journal of Psychiatry, used nationwide registers to identify, from among 1,438,339 people born between 1977 and 2000, 113,906 who sustained a head injury leading to hospital contact. The researchers then followed up these individuals for diagnoses of schizophrenia spectrum disorders, unipolar depression, bipolar disorder, and organic mental disorders made after their 10th birthday.
Head injury at any age was associated with a 65% increase in risk for schizophrenia, with the strongest increase, of 86%, seen for individuals who sustained the injury aged 10 to 15 years. Furthermore, it also raised the risk for depression (incidence rate ratio [IRR]=1.59), bipolar disorder (IRR=1.28), and organic mental disorders (IRR=4.39).
The risk seemed to be larger in the first year after injury than subsequent years, and after exposure to severe head injury, rather than mild injury or skull fracture. However, a dose–response relationship between head injury severity and risk was present only for organic mental disorders.
Even after adjusting for several confounding factors, including epilepsy, the risks for schizophrenia and depression remained significantly elevated.
To control for accident proneness, which might be more common in people who go on to develop psychiatric disorders, the researchers also looked at the effects of fractures not involving the skull or spine. They found that the increase in risk associated with skull fractures exceeded the increase in risk associated with non-skull fractures for schizophrenia, depression, and organic mental disorders, although there was no significant difference for bipolar disorder.
Infections and autoimmune diseases may also increase the risk for psychiatric disorders, and these were independent risk factors in the current study. However, they did not influence the relationship between head injury on risk for psychiatric disorders.
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