There are three distinct types of attention-deficit/hyperactivity disorder (ADHD) that match up with children's personalities, some researchers suggest.
What's more, looking at these ADHD types is better than the current diagnostic methods in predicting which children will go on to develop further mental-health problems, the researchers said in the new study.
The finding of these three types is preliminary, and won't be used in diagnosis anytime soon, but it shows that it's possible to classify mental-health disorders in a manner that's based more on biology than symptoms, which may help researchers better understand the underlying cause of these conditions, the researchers said.
The new findings "set the stage" for improving the classification of mental-health disorders, the researchers said. [Typical Toddler Behavior, or ADHD? 10 Ways to Tell]
If the existence of these three types is confirmed by future research, "it has a lot of implications for targeting interventions more directly to the kids who are most at risk" of developing future problems, said study researcher Sarah Karalunas, an ADHD researcher at Oregon Health & Science University.
As with most mental-health disorders, ADHD is currently diagnosed based on people's behavior — kids with ADHD can have problems holding attention, following instructions and staying in their seat when they're told to. There are currently three types of ADHD: predominantly inattentive, predominantly hyperactive-impulsive and combined presentation (which has symptoms of both inattention and hyperactivity/impulsivity).
However, the criteria currently used to diagnose ADHD do not identify the underlying causes of a child's behavioral problems, and don't tell parents whether their kids' ADHD will get better or worse with time, Karalunas said.
In the new study, the researchers set out to see whether there was a way to divide up children with ADHD that would tell researchers more about the biological causes or future outcomes of the condition, Karalunas said.
The study involved 247 children with ADHD ages 7 to 11, and 190 children without ADHD. Parents answered questions about their child's temperament, such as whether their child likes to be physically active, likes rowdy activity, is warm and friendly, or gets angry when he or she makes a mistake.
A child's temperament emerges very early in life, Karalunas said. It is thought to be based on biological factors, and is related to personality in adulthood.
The researchers then looked to see whether they could group the children based on their temperaments. They found that kids with ADHD clustered into three groups, which the researchers called "mild ADHD," "surgent ADHD" and "irritable ADHD."
Kids with the mild type had ADHD symptoms, including inattention and impulsively, but their temperaments were otherwise similar to those of kids without ADHD. Kids with the surgent type were very excitable and exuberant, with a high activity level. Kids with the irritable type had higher levels of anger, fear and sadness, and were hard to soothe.
The study also found that the children in the three groups had differences in their heart and brain activity. For example, in children with irritable ADHD, the activity of two brain regions — the amygdala and the anterior insula — was less in sync, suggesting that these regions had trouble communicating. The anterior insula is involved in regulating emotions, so the findings seem to agree with what the researchers saw in the children's behavior.
"These kids have a hard time regulating emotion, and we see weak connections in areas that we would expect to help them regulate that emotion," Karalunas said.
The surgent and irritable types seem to be fairly stable over time. More than 70 percent of children who were originally classified as either surgent or irritable were put in those same groups one year later.
And children with irritable ADHD were more likely to develop another mental-health condition, such as mood or anxiety problems, compared with children with the other types of ADHD, or those without ADHD. In contrast, the way that ADHD is diagnosed now does not predict children's outcomes, the researchers said.
Much more research is needed to see if other studies can confirm these ADHD subtypes, or if other ways of dividing children with ADHD might be better, including methods that take genetics into account, Karalunas said.
Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Steven & Alexandra Cohen Children's Medical Center of New York, agreed that the criteria for ADHD stated in the Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition) — the guidebook for diagnosing psychiatric conditions, including ADHD — are imperfect. Alternative approaches for assessing mental-health conditions in children may be particularly useful in helping to distinguish mild cases from children who don't have the disorder, Adesman said.
Still, the new study was small, and it's not clear whether the approach in the study is the best way to refine ADHD classification, Adesman said. Nonetheless, "It's a first step in a different direction, and whether it turns out to be the right direction, only time will tell," Adesman said.
Adesman also noted that the researchers did not directly look at the severity of the children's ADHD, which can be assessed with the DSM, and may be related to kids' chances of developing of more mental health disorders.
The new study is published today (July 9) in the journal JAMA Psychiatry.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.