Study Finds Traumatic Brain Injuries, Even Mild Ones, Increase Risk of ADHD

Joel L. Young, MD

The brain is a plastic organ that changes and reacts to its environment. In recent years, researchers have become increasingly interested in how brain injuries can affect development well into adulthood. More than 300,000 children are treated for traumatic brain injuries (TBI) each year. Two new studies point to a link between childhood TBI and later development of ADHD.

TBI and ADHD: Untangling the Connection
A cohort study that followed 187 children was published in the journal JAMA Pediatrics earlier this year. Each child had been hospitalized overnight for a traumatic brain injury between the ages of 3 and 7 years old. Researchers followed up with participants for several years following the study, and parents completed questionnaires about their children’s behavior and development at regular intervals.

The results suggest that the effects of TBI may extend well beyond the period immediately following the injury. Even as late as 6 years following the injury, children with a TBI history were more likely to have ADHD. Overall, 62% of children who sustained a TBI developed ADHD, compared to 15% of the non-TBI cohort.

New research published within the past few months arrives at similar conclusions. That study, published in the journal Biological Psychiatry, compared symptoms of ADHD in 418 children with a history of TBI to symptoms in 3,193 children with no prior TBI. They also assigned a genetic risk score to each child. They found that a higher genetic risk score correlated with higher risk of ADHD only in children with no history of TBI. This suggests that genetics may only play a role in ADHD risk in children with no TBI history.

Brain Changes Related to ADHD
Most children who experienced a severe TBI who later developed ADHD began showing symptoms of the disorder within 18 months. However, children with a mild or moderate TBI developed symptoms as late as more than six years following the initial injury.

Participants’ last follow-up visit coincided with many children’s entry into middle school. This is a time when many children must rely more on executive functioning skills. So it’s unclear whether this later development of ADHD coincides with continued brain changes, or is due to increased demands on a child’s brain.

While this research strongly suggests that a TBI may change brain regions associated with ADHD, it did not identify or test a causal connection between ADHD and TBI. More research is needed to fully flesh out this connection. However, other recent research strengthens the connection between ADHD and TBI, and suggests why one might lead to the other.

Does TBI Cause a Distinct Form of ADHD?
Stojanovski and colleagues’ 2018 study published in the journal Biological Psychiatry followed 3,611 youth, 418 of whom who had sustained a traumatic brain injury. Researchers also calculated each participant’s genetic risk score based on known genetic risk factors for ADHD.

Predictably, an increased risk of ADHD was found among participants who had a higher genetic risk score. What was surprising, however, is that there was no increased risk of ADHD among TBI survivors who had a higher genetic risk score. This suggests that ADHD following TBI develops differently, not due to genetic risk.

Brain imaging scans were conducted to look at brain structures associated with ADHD. Researchers found that brain volumes in structures, such as the basal ganglia, linked to ADHD was similar between the two groups. But an analysis that looked at connections between the two brain hemispheres found distinct differences in those with TBI-related ADHD and those with genetic ADHD.

This points to different neural underpinnings for the different manifestations of the disorder. TBI-related ADHD may even be a different disorder altogether.

TBI: A Permanent Injury?
For decades, most researchers thought that, should a person survive and thrive immediately following a TBI. We now know that ADHD is just one potential complication of TBI.

A 2017 study followed 285 patients who sustained TBIs. Researchers then followed a subset of 110 people who showed lingering concussion symptoms for three months or less. Only 27% fully recovered from their symptoms. Of those who did, 67% did so within the first year.

This suggests not only that symptoms following a TBI are common, but that the longer they last, the more likely the symptoms are to be permanent. The authors of that study emphasize the need for further research to better understand and interpret their findings.

The data is compelling, suggesting a clear relationship between brain damage and ADHD. We don’t yet know what this means, whether there may be interventions that can prevent ADHD, or to what extent TBI-related ADHD differs from traditional ADHD.

Clinicians must be mindful of the potential impacts of brain injuries, and should urge patients to seek prompt treatment for any new symptoms following a head injury.

References:
Bowser, A. D. (2018, April 16). Children, adolescents with TBI at risk of secondary ADHD. Retrieved from https://www.mdedge.com/pediatricnews/article/161152/mental-health/children-adolescents-tbi-risk-secondary-adhd

Long-term consequences of TBI. (n.d.). Retrieved from http://ohiovalley.org/informationeducation/long-termconsequences/

Stojanovski, S., Felsky, D., Viviano, J. D., Shahab, S., Bangali, R., Burton, C. L., . . . Wheeler, A. L. (2018). Polygenic risk and neural substrates of attention-deficit/hyperactivity disorder symptoms in youths with a history of mild traumatic brain injury. Biological Psychiatry. doi:10.1016/j.biopsych.2018.06.024

Study identifies distinct origin of ADHD in children with history of brain injury. (2018, August 14). Retrieved from https://www.sciencedaily.com/releases/2018/08/180814101302.htm

Traumatic brain injury & concussion. (2017, April 27). Retrieved from https://www.cdc.gov/traumaticbraininjury/get_the_facts.html
Hiploylee, C., Dufort, P. A., Davis, H. S., Wennberg, R. A., Tartaglia, M. C., Mikulis, D., . . . Tator, C. H. (2017). Longitudinal study of postconcussion syndrome: Not everyone recovers. Journal of Neurotrauma, 34(8), 1511-1523. doi:10.1089/neu.2016.4677

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