ADHD not caused by head injury - report

Children who develop ADHD in later life may have been more likely to suffer injuries as an infant, according to research out today.

While head injuries do not cause attention deficit hyperactivity disorder (ADHD), they can be an early sign of a later diagnosis of the condition, researchers said.

This may be because children who go on to develop ADHD take more risks as youngsters, and are therefore more likely to suffer head injuries.

Children with ADHD display behavioural problems such as inattentiveness, hyperactivity and impulsiveness.

Common symptoms include a short attention span, restlessness, being easily distracted and constant fidgeting.

ADHD is estimated to affect between 3% and 9% of school-age children and young people.

For the latest study, experts from the US analysed data from 62,088 UK children, of which 2,782 (4.5%) had a head injury and 1,116 (1.8%) had a burn injury.

They were trying to discover if suffering an injury as a child could lead to the development of ADHD, but they found no evidence of a direct link between the two.

Writing in the British Medical Journal (BMJ), the experts concluded: “This study found that children with a head injury before age two were twice as likely to be diagnosed as having ADHD as a population based comparison group, but not more likely to be diagnosed as having ADHD than another medically attended injury group (burn injury).

“Thus, contrary to our hypothesis, the head injury itself does not seem to be causal in the development of ADHD.

“Rather, some other factor seems to be associated generally with early injury and the development of ADHD.

“These results indicate that medically attended injury before age two may be an early marker for behavioural traits that lead to diagnosis of ADHD.

“We find it plausible that children who go on to develop clinical ADHD exhibit more risk-taking behaviours as young children, and are therefore more likely to be injured before age two.”

Guidelines from the UK's National Institute for Health and Clinical Excellence (nice) state that risk factors for ADHD may interact rather than act in isolation.

For example, genetics is important, but environmental factors such as injury or whether the mother smoked may also contribute.

Previous studies have shown that injury is more common in children with ADHD, and that moderate to severe traumatic brain injury in school age children results in the development of ADHD.

In an accompanying editorial, Morris Zwi, a consultant child and adolescent psychiatrist from London, and Philip Clamp, a GP from Richmond, said the findings were important.

“They indicate that primary care clinicians should assess children with injuries for symptoms of ADHD and continue to monitor them over time,” they said.