Study raises questions about the diagnosis and medical treatment of ADHD

New ways of thinking about the disorder are needed, say researchers.

A new UCLA study shows that only about half of the children diagnosed with attention deficit hyperactivity disorder, or ADHD, have the cognitive deficits usually associated with the condition.

The study also found that in populations where medication is rarely prescribed for ADHD, the prevalence and symptoms of the disorder are roughly the same as in populations where medication is widely used.

The findings of the first large longitudinal study of adolescents and ADHD, carried out in the population of northern Finland, were published in several articles in a special section of the Journal of the American Academy of Child and Adolescent Psychiatry, which appeared in December.

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Source: https://www.eurekalert.org/news-releases/660353

ADHD is a common chronic behavioural disorder characterised by inattention, hyperactivity and impulsivity, thought to affect 5 to 10% of school-age children worldwide.

In adolescence, ADHD is usually associated with cognitive deficits, particularly in working memory and inhibition, which have been linked to overall intelligence and academic achievement, according to Susan Smalley, professor of psychiatry at UCLA. Interestingly, the study showed that these deficits are present in only about half of the adolescents diagnosed with ADHD.

Part of the explanation may lie in the common method used to diagnose the disorder. ADHD is an extreme on a normal continuum of behaviour that varies across the population, just like height, weight or IQ. Its diagnosis, and therefore its prevalence, depends on where health professionals “draw the line” on this continuum, based on the severity of symptoms and overall impairment. However, the study showed that children with cognitive deficits are no more prone to heightened levels of inattention or hyperactivity than other children diagnosed with ADHD, suggesting that behaviour rating scales are not sensitive enough to tell the two groups apart.

Additional psychological testing is recommended to confirm the presence of cognitive impairment.

The researchers also found surprising results regarding the effectiveness of medication in treating ADHD. Unlike children in the United States, young people in northern Finland are rarely treated with ADHD medication, yet the picture of the disorder (its prevalence, symptoms, psychiatric comorbidity and cognition) is relatively similar to that in the United States, where medication is widely used. The researchers point out that this raises important questions about how effective current ADHD treatments are in tackling the long-term problems of the disorder.

“We know that medication is very effective in the short term,” said Smalley, author or co-author of each of the articles. “But the study raises important questions about the long-term effectiveness of ADHD treatment: we have two different cultures and two different approaches to treatment, but by adolescence there is little difference in how ADHD presents and in the problems associated with it.”

Other findings from this large study include:

• Further confirmation that ADHD symptoms change with age: hyperactivity and impulsivity decrease with age, while inattention becomes increasingly predominant. In fact, about two-thirds of children with ADHD continue to show significant levels of inattention and impairment in adolescence.
• ADHD is associated with higher rates of other psychiatric problems. The most prominent in adolescence are depression; anxiety; oppositional behaviour, such as arguing, losing one's temper and being easily annoyed; and conduct disorders such as vandalism and truancy. Surprisingly, post-traumatic stress disorder is significantly higher in adolescents with ADHD than in young people without ADHD. The prevalence of these co-occurring disorders is comparable to that seen in other ADHD populations around the world.
• Two genes, called DBH and DRD2, which are involved in regulating dopamine (a neurotransmitter involved in attention, motivation and emotion), were also associated with ADHD in the northern Finnish population. Although the researchers involved say they probably account for very little of the genetic variation underlying ADHD, the findings lend further support to the role of the dopamine pathway in the aetiology of the condition.

“This set of articles highlights the need to engage in new ways of thinking about ADHD,” said Smalley, who is also a member of the Center for Neurobehavioral Genetics at UCLA. “It is certainly a valid disorder, but predispositions to ADHD are part of the normal variation in attention and activity, much like diabetes and glucose tolerance, or dyslexia and reading impairment.

“The continuous nature of susceptibility to ADHD requires us to look more closely at which environmental pressures may lead to impairment, rather than broadening our diagnostic classifications even further,” she said.

The study began in 1986, when researchers from Imperial College London and the University of Oulu in Finland began studying 9,432 children in northern Finland. They followed the children from early pregnancy to adolescence (ages 16 to 18). UCLA researchers then joined forces with them to examine ADHD behaviours in the adolescents, using a standard screening survey and diagnostic criteria. Of the 6,622 survey respondents, a subset of 457 probable cases and controls were assessed for ADHD and other psychiatric disorders. The estimated prevalence of ADHD in these adolescents was 8.5%, with a male-to-female ratio of 5.7 to 1.

In addition to Smalley, the UCLA researchers involved in the study included Lorie A. Humphrey, Sandra K. Loo, James T. McCracken, James J. McGough and Stanley F. Nelson.

Mark Wheeler, 22 January 2008