Childhood ADHD is a major public health problem, with prevalence estimated to be over 5 million children in the US alone. Of particular concern is the recent increase in diagnosis of the disorder. In 2011, the CDC estimated that nearly 9% of children in the US (1 of 11 children between the ages of 5 and 17) have ADHD; the diagnosis is made in approximately twice as many boys as girls.1 Moreover, ADHD rarely exists alone. In most children with ADHD (75% to 80%), a second (or even third) psychiatric disorder develops at some point in their lives.2
The changing face of ADHD
While the overall prevalence of ADHD among children and adolescents has increased in the past 10 years, diagnosis among girls appears to have increased more rapidly. In the 1990s, the male to female ratio for ADHD was estimated to be about 9 to 1 in clinical settings and 3 to 1 in the general population.3 More recently, however, a large epidemiological study of 3907 children found that of the 8.7% who met DSM-IV-TR criteria for ADHD, 51% were boys and 49% were girls.4 The prevalence of ADHD is reportedly higher in women than in girls, which suggests that ADHD may be underdiagnosed in girls or, alternatively, that the developmental onset of impairing symptoms occurs later in girls than in boys.5
The rise in diagnosis of ADHD among girls contributes to the changing face of the disorder. For example, although there are few reported sex differences in problem behavior in infancy and early childhood, sex differences appear to emerge by age 4 years, with boys showing more aggressive and impulsive behaviors.
Two hypotheses have been posited to explain this apparent “remission” of symptoms in young girls. The first is that girls are more likely to channel their problem behavior into internalizing behaviors. In females, ADHD appears to be associated more with anxiety and depression—two-thirds of women with ADHD have comorbid depression.6The second hypothesis is that the change in behavior among girls is a function of more rapid neurobiological, cognitive, motor, and social development.7On one hand, this more rapid rate of development among girls may be protective against the manifestation of some ADHD symptoms in childhood; on the other hand, the onset of pubertal increases in estrogen and subsequent increases in dopamine receptors lead to an acceleration of symptoms in adolescence.8
ADHD is nevertheless associated with significant risks for adverse outcomes. Longitudinal studies suggest that individuals with ADHD are far more likely than those without the disorder to drop out of school, to have few or no friends, to underperform at work, to engage in antisocial activities, and to use tobacco or illicit drugs. Also, youths with ADHD are more likely to experience teen pregnancy and sexually transmitted diseases, to drive too fast and have multiple car accidents, and to experience other psychiatric conditions as adults.9
What is already known about ADHD in boys and girls?
? ADHD is a neurodevelopmental disorder in which symptoms begin (most often) in preschool years and persist into adulthood. ADHD is more commonly diagnosed in boys than in girls; however, the rate of diagnosis among girls is rapidly increasing.
What new information does this article provide?
? Boys with ADHD can present with different cognitive and behavioral patterns than girls with ADHD. These differences may be because of the types of comorbid conditions, earlier maturation among girls, and failure to identify the more subtle patterns of symptoms in girls. Despite these factors, girls with ADHD remain at significant psychosocial risk into adulthood.
What are the implications for psychiatric practice?
? Up to 75% of persons with ADHD have at least one other psychiatric disorder, which often makes treatment more challenging. Assessment for and diagnosis of ADHD in girls are more complicated than in boys, because of later onset, more subtle clinical manifestations, and wording in many popular ratings scales that emphasizes behaviors seen more commonly in boys. Children who are young for grade in school tend to be rated as having more symptoms of ADHD than those who are older for grade, leading to greatest rates of ADHD diagnosis among children whose birthday is just before the cutoff for school entry. Given the proposed changes for ADHD diagnostic criteria in DSM-5, it is likely that rates of diagnosis among girls will continue to increase.
The sex paradox posits that the sex in which a given disorder is less prevalent should show greater levels of impairment than the sex in which the disorder is more prevalent.10While initial studies suggest that girls with ADHD have better adolescent and adult outcomes than boys with ADHD, more recent findings indicate that girls with ADHD have considerably more functional impairment, including an increased risk of internalizing disorders (eg, depression, suicide), and eating pathology than girls without ADHD.3,11,12
These observations occur despite the fact that with age, symptoms of hyperactivity/impulsivity decline more in girls than in boys.13In fact, a recent study found that by adolescence, only 16% of girls with ADHD showed adequate social adjustment compared with 86% of girls without ADHD.14 Another 5-year follow-up of 6- to 17-year-old females with ADHD found that by age 16, ADHD persisted in 71% of the sample.15 Girls who have a diagnosis of ADHD in childhood continue to show deficits in executive functions as adults, even if their symptoms have remitted to a nondiagnosable level.16
Early studies that compared neuropsychiatric function in boys who had ADHD with that of girls who had ADHD may have been confounded by group differences in proportion of ADHD subtype, since among school-aged children with ADHD, girls routinely present more often with the inattentive subtype, while boys are more likely to present with the combined subtype.13 Not surprisingly, an early meta-analysis that examined sex differences in ADHD found that boys with ADHD had greater levels of hyperactivity symptoms and externalizing behaviors, which were associated with reduced academic skills.11
More recent neuropsychological studies suggest that when samples of boys and girls with ADHD are matched on subtype, girls are often just as impaired as boys, and in some functional areas (eg, planning skills), more impaired than boys.16,17 Other studies found that individuals with the subtype less common for their sex (ie, boys with the inattentive subtype and girls with the combined subtype) are at increased risk for cognitive dysfunction.18
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