People with attention-deficit hyperactivity disorder (ADHD) have distinct differences in their brain structure, a new study finds, suggesting the disorder should be considered a neurological condition and not simply a behavioural problem.

The research — published Wednesday in Lancet Psychiatry — was described by its authors as the largest-ever review of ADHD patient brain scans.

The scientists evaluated MRI scans and other data from more than 3,200 people, comparing 1,713 patients who had been diagnosed with ADHD to a control group. The patients ranged in age from four to 63.

The researchers found those with ADHD had smaller brain volume in five subcortical regions, as well as an overall smaller brain volume.

The phenomenon was greatest in children and less notable in adults.

The most noteworthy findings relate to the smaller amygdala and hippocampus in patients with ADHD, as those regions haven’t previously been conclusively linked to the disorder.

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“Both of those brain regions are associated with emotional processing. And those types of emotional symptoms [such as impulsivity] are very common in ADHD, but aren’t given as much attention or focus as the cognitive symptoms that we see in the disorder,” says Dr. Jonathan Posner, an associate professor of psychiatry at New York’s Columbia University Medical Center.

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ADHD causes inattention, hyperactivity and impulsivity — and at least one in 20 children in Canada are estimated to have the disorder.

Posner wasn’t involved in the study, though he did publish a commentary in the same edition of Lancet Psychiatry based on the research.

The findings are important, he adds, because they verify the results of earlier studies considered too small to be conclusive.

And while the findings can’t conclude whether brain abnormality is a cause of ADHD or the result of it, Posner says they suggest the behavioural problems in children with ADHD are actually neurological.

‘It is a bit distressing’

Toronto pediatric neurologist Dr. Evdokia Anagnostou agrees, saying she hopes this research will help dispel misconceptions about children with the disorder.

“It is a bit distressing that kids are still getting feedback that they are misbehaving or that [ADHD] is not real. If anything comes out of this very large study, it’s that this is a brain disorder,” she says.

Diagnoses of ADHD have become increasingly common — at least one in 20 children in Canada are estimated to have the disorder.

Still, the behavioural problems that accompany ADHD are often dismissed as “just lazy parenting, too much sugar, too many video games, undisciplined kids, lazy kids, et cetera,” says Heidi Bernhardt, executive director of the Centre for ADHD Awareness Canada.

For those who live and work in the field, she says the study’s findings could assist in erasing some of the stigma and misinformation surrounding the disorder.

As far as using MRIs or brain scans to diagnose ADHD, Posner says it’s too early to consider that.

The research was conducted by the ENIGMA ADHD working group, a consortium of scientists from some of the world’s most prestigious universities, hospitals and research institutes.

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