Attention-deficit/hyperactivity disorder (ADHD) is one of the most common behavioral disorders in children. When adults are diagnosed with ADHD it is seen as a continuation of the same. New research from King’s College London explores adult ADHD as distinct from the childhood version: though late-onset and early-onset ADHD may be related, might they be caused by unique factors and also require separate treatments?

Among their theories, the researchers suggest symptoms of other disorders, such as obsessive-compulsive disorder or low-level anxiety, may underlie some diagnoses of adult-onset ADHD.

In other words, a late diagnosis may simply be a misdiagnosis for some.

Medicalization

Three symptoms characterize ADHD: inattention, hyperactivity, and impulsivity. Poor focus and disorganization are elements of inattention. Hyperactivity includes fidgeting and constant movement. Impulsivity causes a person to act hastily without first thinking about consequences or harm. While some people display only one or two symptoms, other people behave in ways revealing the entire trio of common traits.

In the United States, the prevalence of a diagnosis of ADHD has increased over time, the Centers for Disease Control and Prevention reports. In 2003, 7.8 percent of children received an ADHD diagnosis; in 2007, the proportion increased to 9.5 percent; and in 2011, the most recent statistical year, more than one in 10 children — 11 percent — had been diagnosed. While the average age of ADHD diagnosis was 7, children with more severe ADHD are diagnosed earlier. More boys than girls are diagnosed, the CDC notes, and prevalence varies by state, from a low of 5.6 percent of all children in Nevada to a high of 18.7 percent in Kentucky.

Dr. Peter Conrad of Brandeis University observes how world views of ADHD have changed over time. Beginning in the 1960s, the diagnosis was primarily used in North America until the 1990s when diagnosis and treatment increasingly began to be applied internationally. In particular, he identifies and describes several engines facilitating the “migration” of the ADHD diagnosis, including the role of the Internet with the related advent of online screening checklists, advocacy groups, and the transnational pharmaceutical industry.

“I’m not suggesting that no one benefits from drugs, I am not anti-drugs,” Conrad said in a 2013 lecture at University of New Mexico, further explaining that medicalization (like urbanization, say, or industrialization) is not necessarily good or bad, it just is. “My biggest concern about medicalization… is the patholigization of everything, turning all human difference into some kind of medical disorder.”

Anxiety or Adult ADHD?

For the current analysis, the researchers sampled the Environmental Risk (E-Risk) Longitudinal Twin Study and focused on 2,232 British participants. To assess symptoms of childhood ADHD, the researchers collected mother and teacher reports at the ages of 5, 7, 10, and 12. To diagnose adult ADHD, the researchers conducted private interviews with the participants at age 18 and applied DSM-5 standards to symptoms of inattention and hyperactivity-impulsivity.

In total, 247 participants met diagnostic criteria for childhood ADHD while 166 participants had adult ADHD. Two thirds of these cases could be described as late-onset ADHD, in that they had not been diagnosed in childhood. Late-onset individuals were more likely to be female, had fewer externalizing problems, and higher IQ compared with individuals with ADHD that persisted from childhood through adulthood.

Because the study was a cohort of twins, the researchers also analyzed the potential genetic basis of the disorder. They discovered adult ADHD was less heritable than the childhood version. The team also found that having a twin with childhood ADHD did not place a person at higher risk of developing late-onset ADHD.

Based on their work, the researchers speculate three possible explanations for adult ADHD. First, late-onset ADHD may simply be masked during childhood due to, say, high intelligence or a supportive family environment, with the symptoms becoming known later. A second possibility is that people diagnosed with late onset may not have ADHD but another disorder with similar symptoms, such as anxiety. Third, the team proposes adult ADHD may be a distinct disorder.

Dr. Stephen V. Faraone and Dr. Joseph Biederman favor the first theory of “subthreshold symptoms.” In an editorial, they argue that many years may separate barely noticeable symptoms and ultimate impairment, “particularly among individuals with strong intellectual abilities and those living in supportive, well-structured childhood environments.” This “scaffolding,” they argue, would help a person compensate in early life, “only to decompensate into a full ADHD syndrome when the scaffolding is removed” in adulthood.

Source: Agnew-Blais JC, Polanczyk GV, Danese A, et al. Evaluation of the persistence, remission, and emergence of Attention-Deficit/Hyperactivity Disorder in Young Adulthood. JAMA Psychiatry. 2016.