November 12, 2008 — Young children with medically attended injury before the age of 2 years are more likely to have a subsequent diagnosis of attention-deficit/hyperactivity disorder (ADHD), a new study suggests.
However, and perhaps surprisingly, early head injury requiring medical attention appears to carry the same magnitude of risk as other types of injury.
Investigators at the University of Utah, in Salt Lake City, found that children who sustained a medically attended burn or scald injury or head injury before the age of 2 years were almost twice as likely to be diagnosed with ADHD by the age of 10 years, compared with noninjured children.
"Very young children may exhibit behavioral traits that put them at risk for injury, and these traits may be early manifestations of ADHD," lead author Heather T. Keenan, MDCM, PhD, told Medscape Psychiatry.
The study is published online November 6 in BMJ.
Association Not Clear
Previous research has established a link between head injury and ADHD, but the direction of the association is not clear.
To investigate whether medically attended head injury before the age of 2 years increases ADHD risk, the researchers performed a retrospective cohort study of children from 308 primary-care practices in the United Kingdom.
The study involved 62,088 children who were registered in the database from birth to the age of 10 years during 1988 to 2003 and who did not have a diagnosis of ADHD before their second birthday.
The cohort was divided into 3 groups:
2782 children who had a medically attended head injury before the age of 2 years.
1116 children who had a medically attended burn injury before the age of 2 years.
58,190 children with neither injury before the age of 2 years.
Of the total cohort, 1.5% of the children were diagnosed with ADHD between age 2 and 10 years. Of the 6.3% of children with early brain injury or early head injury, however, 11.3% had a subsequent diagnosis of ADHD.
The risk of ADHD diagnosis was almost equally elevated in children with early burn injury and children with early brain injury compared with the other children, even after adjustment for relevant cofactors.
Risk of ADHD Diagnosis Before Age 10 Years, Early Injury vs No Early injury
Injury Before Age 2 Years Adjusted Relative Risk (95% CI)*
No head injury or brain injury 1.0
Head injury 1.9 (1.5 – 2.5)
Brain injury 1.7 (1.2 – 2.5)
*Adjusted for sex, prematurity, Townsend index (socioeconomic status), and practice identification number.
The researchers conclude that medically attended injury may be an early marker for behavioral traits that lead to a diagnosis of ADHD.
"The results emphasize the importance of obtaining preinjury developmental status when examining the relation of head injury to neurodevelopmental consequences," they write.
Although large and therefore powerful, the study data set does not have good measures of injury severity or a controlled method of diagnosing ADHD, said Dr. Keenan. "Therefore, these results need to be duplicated in a prospective cohort study," she said.
Close Follow-up Needed
In an accompanying editorial, Morris Zwi, MB, from Richmond Royal Hospital, in the United Kingdom, and Philip Clamp, MD, from St. John's Surgery, in Bromsgrove, the United Kingdom, say the study has important implications, particularly for primary-care physicians, who should assess and continuously monitor children with injuries for ADHD symptoms.
"A known barrier to referral of children with ADHD to specialist services by primary-care doctors is nonrecognition of the disorder's symptoms. Early assessment and referral to preventive programs, such as parent training, can reduce symptoms. Referral to a specialist team may be useful where problems persist," they write.