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Introduction
Attention deficit hyperactivity disorder (ADHD) is a well-known childhood disorder that often continues into adulthood with a reported prevalence of 3-5% in the general population. Of those with ADHD in childhood, 30-50% continue to show symptoms of the disorder in adulthood (Mannuzza et al. 1991). Principal symptoms of ADHD include inattention, hyperactivity and impulsivity. Based on the presentation of these symptoms in individual patients, the DSM-IV (APA, 1994) specifies three diagnostic subtypes of ADHD, including a predominantly inattentive subtype, a predominantly hyperactive-impulsive subtype, and a subtype that combines inattention with hyperactivity.
Recent studies addressing the expression of symptoms of ADHD in adults raise the possibility that symptoms of ADHD show systematic differences in clinical presentation in relation to age and gender. Specifically, although symptoms of inattention are likely to remain stable throughout life (highlighting the importance of attention problems in this disorder), evidence suggests that symptoms of hyperactivity and impulsivity may wane with increasing age (Biederman et al. 2000). Furthermore, in addition to the age-related changes, an emerging body of literature indicates that symptoms of ADHD may differ in females and males. In the early ages, marked differences are observable in the prevalence of ADHD between the two genders even though symptoms of ADHD emerge early in childhood in both genders, with a mean age of onset between infancy and 7 years (Barkley, 1988). A prevalence of 5-7% has been reported in boys and 2-4% in girls (Barkley et al. 1990). In addition, research has found that girls have fewer symptoms of ADHD than boys (McDermott, 1996), although several investigations have reported contrary results (e.g. Horn et al. 1989).
With regard to gender differences in ADHD, another emerging area of inquiry is the difference in the prevalence of co-morbid disorders between the two genders. Community-based studies with children suggest that girls with ADHD may display a different pattern of co-morbidity than boys. In particular, girls with ADHD may have greater prevalence of co-morbid internalizing and learning problems, whereas boys may display a greater prevalence of disruptive behavioral disorders (Berry et al. 1985; Biederman et al. 2002).
To date, only a few studies have explored the difference in distribution of ADHD subtypes between the two genders. In the pediatric...