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Jim came to see me complaining that he feels restless all the time. “What is wrong with me? I constantly find myself fidgeting. I have trouble finishing things that bore me. I can’t sit still for long periods of time.”

Sally is now 25-years-old and has noticed how much her inattention is creating problems at her job. At home, she easily loses things, can’t get organized and is highly distractible. Her friend, who has been diagnosed with ADHD since childhood, told her to be evaluated. “You have a lot of the same issues I do. Maybe you have ADHD.” But Sally or Jim were never diagnosed with ADHD as children. Is it possible they could develop ADHD as adults?

One of the reasons ADHD diagnosis can be confusing to people is that childhood symptoms can look different than adult symptoms. Both groups struggle with inattention, hyperactivity and impulsiveness, but the way those symptoms play out in a person’s adult life can be different.

For example, a “hyperactive” adult looks more like Jim. Whereas a child may run and climb excessively, squirm in class and talk excessively. In terms of inattention, you often see children making careless errors on school work, whereas adults may lose track of time when trying to complete a task. Impulsive children blurt out answers during class and have difficulty waiting their turn on the playground. Impulse adults may present more with impulsive spending and not censoring their comments. The point of these examples is that ADHD symptoms can present differently in adulthood than childhood.

In diagnosing ADHD, the assumption has been that even though adult ADHD symptoms may look different, the disorder is a continuation from childhood. Yet, there appear to be some adults diagnosed with ADHD as adults who do not report childhood histories consistent with ADHD. That group is of interest and is being studied. Three recent studies point to possible adult onset for ADHD.

Study 1: Is Adult ADHD a Childhood-Onset Neurodevelopmental Disorder?

In the study "Is Adult ADHD a Childhood-Onset Neurodevelopmental Disorder" it followed 1037 children born in New Zealand to the age of 38. All met criteria for diagnosis of ADHD. Data was obtained from multiple sources like teachers, parents, testing, neuropsychological deficits, etc. The study concluded that 90 percent of the adults followed did not have childhood history of onset. This finding led to the question, is it possible that adults with ADHD symptoms do not have to have a history of childhood-onset disorder? If so, what is the causing adult symptoms?

Study 2: Attention-Deficit Hyperactivity Disorder in Adults

In the study "Attention-Deficit Hyperactivity Disorder in Adults" it followed 5249 people raised in the same town in Brazil from birth to ages 18-19. At age 11, 9 percent of the children in the study met criteria for the DSM-5 diagnosis of ADHD. The researchers also found that adult onset looked different than childhood, and wondered if childhood vs adult onset of ADHD represents two different syndromes. A question was raised as to whether or not the subjects in this study who appeared to be adult- onset only had childhood symptoms that went unreported.

Study 3: Attention-Deficit/Hyperactivity Disorder Trajectories From Childhood to Young Adulthood

This study, called "Attention-Deficit/Hyperactivity Disorder Trajectories from Childhood to Young Adulthood," the researchers were interested in assessing childhood risk factors and young adult functioning. They studied a large sample of same gendered twins at various ages (5,7,10,12 and 18 years). Based on a sample of 247 people who met the diagnostic criteria for childhood ADHD, the researchers concluded that there is a difference between late and early onset of ADHD, but the symptoms look similar. A significant 68 percent of their sample did not meet criteria for the diagnosis of ADHD in childhood.

These studies support the idea that adult onset is possible. However, there are a few concerns. One question for all three studies is, because childhood symptoms were not reported, does that mean they were not present? And even in the cases in which people didn’t make full criteria for diagnoses, clinically significant symptoms persisted in two-thirds of the patients.

What is notable is that we seem to see adult ADHD occurring without childhood onset in some cases. This means it is important to continue to study this subset of ADHD adults and see how they differ.

Related to this is the observation that some adults seem to grow out of childhood ADHD. Why is this? Dr. Philip Shaw at the National Human Genome Research Institute and his colleagues decided to try to find out. In their work, they found differences in the brain structures of the cortical regions that control attention. In those children who continued ADHD into adulthood, they found differences in patterns of brain growth from those children who did not continue the symptom picture into adulthood. This difference in cortex development may be a predictor of who continues with ADHD symptoms and who might grow out of the diagnosis. More work is needed. But this could be evidence for the biological continuation of ADHD into adulthood for those with childhood onset.

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