Study Suggests ADHD in Adults May Be Distinct Disorder

A study published May 22 in AJP in Advance suggests that adults presenting with ADHD symptoms may not have a childhood-onset neurodevelopmental disorder.

The study followed a cohort of 1,037 people who were born in Dunedin, New Zealand, in 1972 and 1973 and were followed for nearly four decades with comprehensive interviews and health evaluations—including psychiatric and neuropsychiatric tests—at periodic intervals.

In line with other prevalence data, childhood ADHD was diagnosed in 61 study participants (about 6 percent), mostly in boys. Adult ADHD was diagnosed in 31 individuals (3 percent), with equal gender distribution.

Those 31 people were not simply children who failed to manage their symptoms; only three of the 31 ADHD adults had a childhood ADHD diagnosis.

“What’s more, the adults diagnosed with ADHD showed almost none of the neuropsychological deficiencies that are a hallmark of childhood ADHD,” said lead study author Terrie Moffitt, Ph.D., the Knut Schmidt Nielsen Professor of psychology and neuroscience at Duke University. “Their brains seemed to work just fine when taking IQ or working memory tests.”

In comparison with test scores, however, those adults with ADHD did report cognitive problems, such as forgetting why they went to a store or having trouble finding words when speaking.

Another difference was that the adult ADHD cases had much higher rates of substance abuse (around 48 percent) than those diagnosed as children.

These are interesting discrepancies that Moffitt thinks will be subject to interpretation. “Hard-nosed types who view ADHD as an overdiagnosed condition might see the normal neuropsychological profiles and elevated substance use as evidence that adult ADHD is not a genuine disorder,” she told Psychiatric News.

“Others would argue that since over half of the cases had no diagnosed disorder, it serves as evidence that adult ADHD is a real and distinct problem. And while we don’t fully understand it yet, the people who have it deserve mental health care.”

No matter one’s interpretation of the findings, Moffitt hopes this study can fuel further research that may help clarify the matter in either direction. There are other longitudinal studies examining ADHD in different populations, so more population evidence should be available in the near future.

And if these current findings are replicated, Moffitt believes changes should be made to the DSM-5 to categorize ADHD as a distinct, non-neurodevelopmental disorder.

To help determine where this condition might fit, Moffitt’s team is moving forward and analyzing the genetic data collected from the Dunedin cohort. Their current study found that unlike childhood ADHD cases, people with adult-onset ADHD did not have a genetic profile associated with an elevated risk of ADHD, which suggests the two disorders are biologically distinct. She hopes to study this in more detail to see what genetic influences may contribute to an adult-onset ADHD and if these differences are shared among any other disorders.

This study was funded by the National Institute on Aging, UK Medical Research Council, and Jacobs Foundation. The study participants were members of the Dunedin Multidisciplinary Health and Development Study. ■