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The head injury is not a cause of ADHD, but rather a result of excessive risk-taking, according to the paper published in the Nov. 8 online edition of the British Medical Journal.
"There have been studies done that link moderate to severe traumatic brain injury in older children to ADHD," said lead researcher Dr. Heather Keenan, an associate professor of pediatrics at the University of Utah in Salt Lake City. "There has been some suggestion that mild traumatic brain injury could also be linked to ADHD."
The researchers wanted to know whether or not head injury that occurs before the age of 2 might cause ADHD. A diagnosis of ADHD cannot be made before that age, Keenan noted.
"It is hard to figure this out, because we don't know whether or not the kids would have gone on to develop ADHD regardless of the head injury," Keenan said.
For the study, Keenan's group collected data on 62,088 children who were registered in a British health improvement network database. The researchers compared the children with head injuries to two other groups: children with a burn/scald injury before the age of 2, and all the other non-injured children.
"We wanted to make sure that if we saw a relationship between head injury and ADHD, it wasn't just that kids with early injuries were showing behavioral traits that would make them more likely to be diagnosed versus the head injury itself," Keenan said.
The researchers found that children with early head injury did have a 90% higher incidence of ADHD diagnosis before they were 10, compared with children in the general population. However, children with a scalding injury also had a higher risk of being diagnosed with ADHD, 70% to be exact. "Therefore, the head injury did not appear to cause the ADHD," Keenan said.
Keenan thinks this finding may mean that some very young children are already showing behavioral traits that are the hallmarks of ADHD.
"Children with early injury should receive routine developmental and behavioral surveillance by their pediatrician, as well as injury prevention counseling," Keenan said. "Early injury may be an indicator of attention problems in some children."
Dr. Jon A. Shaw, director of the Division of Child and Adolescent Psychiatry and Behavioral Sciences at the University of Miami, agreed that early injury may signal a future diagnosis of ADHD.
"The finding that head injury or burn injury occurring before 2 years of age are equal risk factors for a diagnosis of ADHD before 10 years of age is a surprising, but interesting, finding," Shaw said.
ADHD is a highly heritable disease. Approximately 85% of ADHD children have a family history of ADHD, Shaw said. "Children with ADHD are impulsive, hyperactive, distractible and inattentive, and are accident-prone, and thus more likely to put themselves at risk for injury," he said.
SOURCES: Heather Keenan, M.D., associate professor, pediatrics, University of Utah, Salt Lake City; Jon A. Shaw, M.D., professor and director, Division of Child and Adolescent Psychiatry and Behavioral Sciences, University of Miami; Nov. 8, 2008, British Medical Journal, online
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