New research published on explores the relationship between head injuries and attention deficit hyperactivity disorder (ADHD). Although there is not enough evidence to state that head injuries in young children cause ADHD, researchers have found that early head injury is indeed associated with a subsequent diagnosis of ADHD.

Professor Heather T Keenan (Dept of Pediatrics, University of Utah) and colleagues note that children who are eventually diagnosed with ADHD tend to engage in riskier behaviors as young children. These behaviors raise their likelihood of becoming injured. However, it is not clear if there is an association between head injury and ADHD. Some studies suggest that children with ADHD are more likely to have been injured, and ADHD is the result of early and severe traumatic brain injury.

The debate continues, though, regarding the actual cause(s) of ADHD. Risk factors given by The National Institute for Health and Clinical Excellence are thought to interact rather than work in isolation. The health authority maintains that although genetics is important, environmental factors such as injury or maternal smoking may also have an impact.

To further investigate the relationship between medically attended head injury before 2 years of age and ADHD, Prof. Keenan and colleagues investigated 62,088 children from 308 general practices in the UK between 1988 and 2003. The data came from the health improvement network database. The study consisted of three groups of children:

  • 2,782 had a medically attended head injury before age 2
  • 1,116 had a medically attended burn or scald without a head injury before age 2
  • 58,190 were not injured before age 2

The researchers hypothesized that the risk of ADHD would be higher in the head injury group if in fact head injury was a causal factor in the development of ADHD.

Results of the analysis showed that compared to non-injured controls, children in both injury groups had similar and significantly higher rates of ADHD. Specifically, having a head injury before age two predicted a doubling in the likelihood of receiving an ADHD diagnosis compared to not having a head injury. There was no difference, however, between the head injury group and the burn injury group.

The authors state that head injury does not seem to be a cause of ADHD, but there are other factors associated with early injury that may be driving the relationship between early injury and development of ADHD. For example, medically attended injury may be an indicator of certain behavioral characteristics that make one prone to receiving an ADHD diagnosis.

In an accompanying editorial, consultant child and adolescent psychiatrist Morris Zwi (St George’s NHS Mental Health Trust, London) suggests that this research “strengthens the hypothesis that the ADHD core symptoms – excessive inattention, hyperactivity, and impulsivity – might be key factors associated with an increased rate of injury.”

“Primary care clinicians should assess children with injuries for symptoms of ADHD and continue to monitor them over time,” concludes Zwi.

Early head injury and attention-deficit/hyperactivity disorder: retrospective cohort study
Heather T Keenan, Gillian C Hall, Stephen W Marshall
BMJ (2008). 337:a1984
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Written by: Peter M Crosta