There's a common myth that most children or adolescents with attention deficit hyperactivity disorder grow out of the condition as they get older.
A new study suggests that it's not that simple.
A University of Cambridge study, published Wednesday in the journal European Child Adolescent Psychiatry, found that young adults who had ADHD when they were younger exhibited differences in brain structure and poorer memory performance compared to their peers who never had the disorder. Aspects of the disorder tended to persist into adulthood, even in those subjects who were not diagnosed as adults.
Roughly 9 percent of children ages 4 to 17 have an ADHD diagnosis, and various estimates suggest that somewhere between 10 and 50 percent of children with ADHD still have the disorder as adults. This has led some psychologists to presume that children commonly "outgrow" ADHD as the brain develops into adulthood. However, the Cambridge study suggests that previous research has failed to take into account changes to the brain that are characteristic of ADHD.
To conduct the study, the researchers followed up with 49 young Finnish people in their early 20s who had been diagnosed with ADHD at age 16. The researchers conducted fMRI scans to examine their brain structure and administered tests of memory function.
What did they find? Regardless of whether or not the young adults still met the diagnostic criteria for ADHD, nearly all showed reduced brain volume and poorer memory function compared to a control group of subjects who had never been diagnosed with the disorder.
Brain volume reductions were observed in the caudate nucleus, a brain region that is associated with the ability to integrate information from different parts of the brain, and is involved in the storing and processing of memories.
To find out how these neural deficiencies manifested themselves, the researchers asked the participants to complete a test of working memory while their brain activity was being measured using fMRI. They found that a third of the subjects who had previously had ADHD failed the memory test, compared to 5 percent of the control group.
The young adults who had had ADHD also showed less activity in the caudate nucleus, which suggests that poor memory may be related to a sluggishness in this part of the brain.
"In the controls, when the test got harder, the caudate nucleus went up a gear in its activity, and this is likely to have helped solve the memory problems," Dr. Graham Murray, a professor of psychiatry at Cambridge and the study's lead author, said in a written statement. "But in the group with adolescent ADHD, this region of the brain is smaller and doesn't seem to be able to respond to increasing memory demands."
Still, these results don't necessarily suggest that all -- or even most -- of the adults should be diagnosed with ADHD again.
"Since part of the diagnosis of ADHD is that not only symptoms are present but that they are impairing life in some way, the study may not contradict previous findings," Dr. Mark Bertin, a developmental pediatrician and author of The Family ADHD Solution, who was not involved in the study, told The Huffington Post in an email. "As well, parts of the brain related to ADHD may mature until almost 30, beyond the age in this study. So people may not experience ADHD-related impairments but still have the sorts of findings seen in the study."
What the findings do suggest is that it may be time to rethink the way we diagnose adult ADHD diagnosis.
"Should we continue to rely on symptom checklists, or should we consider doing laboratory tests?" Murray said in an email to HuffPost. "I’m not suggesting routine MRI scans, but computerised tests of memory function might be important in future, as part of a more holistic assessment."
More research is needed to determine whether ADHD has more or less influence on adults' lives than previously thought. Murray did suggest, however, that more adults may have ADHD than we've realized, and noted that, with growing recognition of the disorder, more people seem to be seeking medical help.
"We are still learning about ADHD in adults, and it is still an under-researched area, but I think there is indeed a growing recognition there are indeed many adults of a whole range of ages who have ADHD and who have never been diagnosed," he said. "Many of these people are now coming forward for treatment."