ADHD symptoms are
sometimes difficult to differentiate from other behavioral disorders.
There is much overlap between ADHD symptoms and the other behavioral
disorders of conduct disorder and oppositional defiant disorder. Among
the behavioral disorders, approximate 90% of children with conduct
disorder would also meet the criteria for oppositional defiant
disorder. Approximately 40% of children with ADHD symptoms also have
oppositional defiant disorder, and about 40% of children with
oppositional defiant disorder also have ADHD. It has been estimated
that between 15% and 20% of children with ADHD symptoms have comorbid
mood disorders (such as depression and anxiety disorders) with 20% to
25% having anxiety disorders and 6% to 20% having learning disorders.
Other conditions which may occur comorbidly (at the same time) with
ADHD symptoms and the behavioral disorders, include Tourette's
disorder, drug and alcohol abuse and dependence, and mental
retardation.
ADHD symptoms and
prevalence:
Studies of ADHD
symptoms and the other two disruptive disorders in community samples
have demonstrated considerable variability, although they are usually
very high. Some of the variability is due to methodological
differences, the use of different systems of classification, and many
other variables. The DSM-IV-TR estimates of prevalence rates for ADHD
range from 2% to 7% in school-age children, although rates as high as
17.1% have been reported in community surveys. Rates for conduct
disorder have been estimated as low as 0.9% for school age children ,
but as high as 8.7% for adolescents. The overall prevalence rate of
oppositional defiant disorder varies across studies from 5.7% to 9.9%.
In school-age children,
boys have a much higher prevalence rate of ADHD symptoms and other
conduct disorders than girls do. In some clinic settings, the ratio of
boys to girls is about 9:1, while in community settings it seems to be
approximately 3:1. It seems, that teachers have a tendency to identify
many more boys having ADHD symptoms than girls. The combined type of
ADHD seems to be much more prevalent among both boys and girls.
However, among children with the hyperactive-impulsive subtype of
ADHD, the male to female ratio is approximately 4:1, while the
inattentive subtype ratio falls to 2:1. In general, the prevalence of
ADHD symptoms seems to decline with age, although some of the more
current studies are finding that the disorder frequently persists into
adulthood. Longitudinal studies are now beginning to identify that the
existing cases of ADHD that persist into adulthood range may range
from 4% to 75%. Once again, the tremendous variability in rates of
occurrence of ADHD symptoms may be accounted for by methodological
differences. Factors that appear to predict persistence of ADHD into
adulthood include a positive family history for ADHD, and also the
presence of other comorbid psychiatric symptoms (particularly
aggression).
