'New ways of thinking' about
the disorder are necessary, researchers say
A new UCLA study shows that only about half of children diagnosed with attention-deficit hyperactivity disorder, or ADHD, exhibit the cognitive defects commonly associated with the condition.
The study also found that in populations where
medication is rarely prescribed to treat ADHD, the
prevalence and symptoms of the disorder are
roughly equivalent to populations in which
medication is widely used.
The results of the first large, longitudinal study
of adolescents and ADHD, conducted among the
population of northern Finland, appeared in
several papers in a special section of the Journal
of the American Academy of Child and Adolescent
Psychiatry published in December and are currently
online.
ADHD is a common, chronic behavioral disorder
characterized by inattention, hyperactivity and
impulsivity that is thought to affect some 5 to 10
percent of school-age children worldwide.
In adolescence, ADHD 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 ADHD.
Part of the explanation may lie in the common
method for diagnosing the disorder. ADHD is an
extreme on a normal continuum of behavior that
varies in the population, much like height, weight
or IQ. 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 ADHD, 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 medicine in
treating ADHD. In contrast to children in United
States, youth in northern Finland are rarely
treated with medicine for ADHD, yet the 'look' of
the disorder its prevalence, symptoms,
psychiatric comorbidity and cognition is
relatively the same as in the U.S., where
stimulant medication is widely used. The
researchers point out that this raises important
issues about the efficacy of the current
treatments of ADHD 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."
Other findings from the wide-ranging study
include:
- Further confirmation that ADHD symptoms do change with age: Hyperactivity and impulsivity decrease with age, while inattention increasingly predominates. In fact, about two-thirds of children with ADHD continue to exhibit significant levels of inattentiveness and impairment into adolescence.
- ADHD 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 ADHD, compared with non-ADHD youth. The prevalence of these co-occurring disorders is comparable to that found in other ADHD populations worldwide.
-
Two genes, labeled DBH and DRD2, involved in the regulation of dopamine a neurotransmitter involved in attention, motivation and emotion have also been associated with ADHD in the population of northern Finland. Although the researchers involved say they likely account for very little of the genetic variation underlying ADHD, the findings further support the involvement of the dopamine pathway in the etiology of the disorder.
"This set of articles brings to light the
necessity of engaging in new ways of thinking
about ADHD," said Smalley, who is also a member of
the Center for Neurobehavioral Genetics at UCLA.
"Certainly it is a valid disorder in terms of its
diagnosis; there are relatively similar
prevalences around the world. But the
predisposition to ADHD is a normal distribution in
attention and activity level, much like diabetes
and glucose tolerance, or dyslexia and reading
disability.
"The continuous nature of liability to ADHD
requires that we examine more carefully what
environmental pressures may be leading to
impairment, instead of broadening our diagnostic
classifications even further," she said.
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). UCLA
researchers then joined in the effort to examine
the adolescents for ADHD 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 ADHD and other psychiatric
disorders. The estimated prevalence of ADHD among
these adolescents was 8.5 percent, with a
male-female ratio of 5.7 to 1.
In addition to Smalley, UCLA researchers involved
in the study included Lorie A. Humphrey, Sandra K.
Loo, James T. McCracken, James J. McGough and
Stanley F. Nelson.
Funding was provided by the National Institute of
Mental Health, the Juselius Foundation in Finland
and the Academy of Finland.
