Recent evidence disputes the theory that head injury early in life increases the risk of developing attention deficit/hyperactivity disorder (ADHD).
There is a well-established link between ADHD and traumatic head injury, with some experts suggesting that brain injury in school-age children causes ADHD. But this has not been conclusively confirmed, and it may be that children with ADHD are more likely to sustain a head injury due to a pattern of riskier behavior.
Writing on the website of the British Medical Journal, Professor Heather Keenan of the University of Utah and her team state that “the direction of the relation between ADHD and head injury has been difficult to elucidate,” but “understanding the nature of the association is important.”
The team explored the link using a database of 62,088 children registered with the National Health Service in the UK. Of the children, 2,782 (4.5 percent) had sustained a head injury before the age of two years. A further 1,116 (1.8 percent) of the children had sustained a burn or scald injury. Among all of the children, 934 (1.5 percent) were diagnosed with ADHD between the ages of two and 10 years.
Analysis showed that the rate of ADHD diagnosis before age 10 was similar in both injury groups, but this rate was significantly higher — approximately double — that of the uninjured children. Previously-injured children made up 6.3 percent of the total number, but 11.3 percent of those with ADHD.
As found in previous studies, ADHD was more common among boys, children who were born prematurely, and those in “more deprived” circumstances as measured by a reliable index. The research also indicates that children with ADHD may be more vulnerable to serious concussion after a brain injury, placing them “at high risk for poor outcomes from subsequent head injuries.”
In an editorial alongside the research report, specialist doctors take up this point, saying that monitoring children with early injuries could reduce later risk of ADHD. Dr. Morris Zwi of South West London and St. George’s NHS Mental Health Trust, London, UK, and Dr. Philip Clamp, a general practitioner in Bromsgrove, Worcestershire, UK, state that both the cause and treatment of ADHD remain uncertain, and have provoked considerable debate.
Concern has been expressed internationally about the increased prescribing of drugs to treat ADHD in children, they write, and international estimates of prevalence vary considerably.
Recently published guidelines from the National Institute for Health and Clinical Excellence and the American Academy of Child and Adolescent Psychiatry conclude that risk factors “may interact rather than act in isolation,” and include genetics and environmental influences such as injury, maternal smoking, maternal alcohol consumption, heroin use in pregnancy, fetal hypoxia (lack of oxygen), exposure to toxins, and zinc deficiency.
But “no validated test is available to confirm the diagnosis,” they write, so “the validity of a diagnosis of ADHD is constantly debated.” The link between head injury and ADHD is complex, they believe, but “the ADHD core symptoms — excessive inattention, hyperactivity, and impulsivity — might be key factors associated with an increased rate of injury.”
Regarding the UK study, they say that the study has limitations. For example, the extent and degree of head injury was unknown, as was the manner in which the diagnoses of ADHD were made.
Nevertheless, “the findings are important. The results indicate that young children who get injured might have more behavioral traits that subsequently attract a diagnosis of ADHD.” Clinicians should assess children with injuries for symptoms of ADHD and continue to monitor them over time, the authors recommend.
This is particularly important as early assessment and referral to preventive programs can reduce symptoms. Help can be sought from child psychologists, child psychiatrists, specialist pediatricians, behavioral neurologists and clinical social workers.
Keenan, H. T. et al. Early head injury and attention deficit hyperactivity disorder: retrospective cohort study. The British Medical Journal, 2008;337:a1984.
Zwi, M. and Clamp, P. Injury and attention deficit hyperactivity disorder. The British Medical Journal, 2008;337:a2244.