Comparison of teens studied in Finland with teens in the USA indicates that symptomatic presentation and prevalence of attention deficit hyperactivity disorder in adolescents are probably similar regardless of whether medication is widely or rarely used, according to related articles in the December issue of the Journal of the American Academy of Child and Adolescent Psychiatry.

The current study was the first large, longitudinal study of adolescents and the disorder, which is thought to affect roughly 5 to 10 percent of school-age children worldwide. The study started in 1986, when researchers from Imperial College, London, and Finland's University of Oulu began studying 9,432 children in northern Finland. They tracked the children from the early fetal period to adolescence (age 16 to 18). Researchers at the University of California at Los Angeles then joined in the effort to examine the adolescents for disorder-related behaviors, using a standard screening survey and diagnostic criteria. Among the 6,622 respondents to the survey, a subset of 457 likely cases and controls were evaluated for attention deficit hyperactivity disorder and other psychiatric disorders. The estimated prevalence of the disorder among these adolescents was 8.5 percent, with a male-female ratio of 5.7 to 1.

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

Part of the explanation may lie in the common method for diagnosing the disorder. The researchers found that the disorder is an extreme on a normal continuum of behavior that varies in the population, much like height, weight or intelligence. Its diagnosis, and thus its prevalence, is defined by where health professionals "draw the line" on this continuum, based on the severity of the symptoms and overall impairment.

However, children with cognitive deficits do not show increased levels of inattention or hyperactivity when compared with other children diagnosed with the disorder, the study found, suggesting that behavior-rating scales alone are not sensitive enough to differentiate between the two groups. Additional psychological testing is recommended to confirm the presence of cognitive impairments.

Researchers also found surprising results regarding the effectiveness of medication. In contrast to children in United States, youth in northern Finland are rarely treated with medicine for the disorder, yet the presentation of the disorder - its prevalence, symptoms, psychiatric comorbidity and cognition - is relatively the same as in the USA., where stimulant medication is widely used. The researchers point out that this raises important issues about the efficacy of current treatments in dealing with the disorder's long-term problems.

"We know medication is very effective in the short-term," said Smalley, who authored or co-authored each of the papers. "But the study raises important questions concerning the long-term efficacy of ADHD treatment. Here we have two different cultures and two different approaches to treatment, yet at the time of adolescence, there are few differences in the presentation and problems associated with ADHD."

The study also provided confirmation that symptoms do change with age: Hyperactivity and impulsivity decrease with age, while inattention increasingly predominates. In fact, about two-thirds of children continue to exhibit significant levels of inattentiveness and impairment into adolescence.

The disorder is associated with increased rates of other psychiatric problems. Most prominent in adolescence are depression; anxiety; oppositional behaviors, such as arguing, losing one's temper and being easily annoyed; and conduct disorders like vandalism and truancy. Surprisingly, post-traumatic stress disorder is significantly elevated among adolescents with the disorder compared with peers without it. The prevalence of these co-occurring disorders is comparable to that found in other ADHD populations worldwide.