Attention-deficit/hyperactivity disorder (ADHD) is one of the most common psychiatric disorders diagnosed in children and adolescents (American Academy of Child and Adolescent Psychiatry, 1997a; Goldman, Genel, Bezman et al., 1998), estimated to affect 3 to 5 percent of school age children (NIH Consensus Statement Online, 1998). The American Psychiatric Association (APA) has proposed a series of diagnostic criteria for ADHD (Appendix A), identifying as the essential feature "a persistent pattern of inattention and/or hyperactivity-impulsivity that is more frequent and severe than is typically observed in individuals at a comparable level of development" (American Psychiatric Association, 1994). Over the years, different terms have been used to describe children with "distractability, impulsivity and usually also overactivity," including minimal brain dysfunction/damage (MBD), hyperkinetic reaction, and hyperkinesis (American Academy of Child and Adolescent Psychiatry, 1997a). ADHD is not a unitary entity. Subtypes of ADHD can be constructed based on differences in phenomenology, comorbidity, and etiology. These different subtypes may differ in etiology, natural history, and response to treatment. The prominence of particular core "symptoms" (they are really signs) of ADHD-inattentiveness, hyperactivity, and impulsiveness-is the basis for the primary distinction among ADHD subtypes. The Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV) distinguishes among a primarily inattentive subtype, a hyperactive-impulsive subtype, and a combined subtype (American Psychiatric Association, 1994). Inattentive ADHD children may be lethargic, shy, and prone to daydream and have a higher incidence of learning disabilities. Hyperactive-impulsive ADHD subjects may be more disruptive and aggressive.

Prevailing opinions regarding the validity of ADHD vary from those who do not believe it exists and regard it as a myth (http://www.healthy.net/library/books/ullman/chap3.htm;">http://www.healthy.net/library/books/ullman/chap3.htm; Weinberg and Brumback, 1992) to those who believe that underlying genetic and physiological evidence supports its existence (Kewley, 1998). Several features of ADHD contribute to the controversy: (1) it is a clinical diagnosis for which no laboratory or radiological confirmatory tests or specific physical features exist; (2) diagnostic criteria have changed frequently; (3) there is no curative treatment, so patients require long-term therapies; (4) therapy often includes stimulant drugs that are thought to have abuse or diversion potential; and (5) substantial differences in the rate of diagnosis and treatment occur across countries, particularly in the United Kingdom, Australia, Canada, and the United States (American Academy of Child and Adolescent Psychiatry, 1997b; Goldman, Genel, Bezman et al., 1998; Kewley, 1998; NIH Consensus Statement Online, 1998; Orford, 1998).

Prevalence estimates of ADHD vary according to the methods of ascertainment, diagnostic criteria, informants, and population sampled (American Academy of Child and Adolescent Psychiatry, 1997a; Elia, Ambrosini, and Rapoport, 1999; Goldman, Genel, Bezman et al., 1998). According to the DSM-IV, the prevalence of ADHD among school-age children is 3 to 5 percent (American Psychiatric Association, 1994). However, prevalence studies using the two previous versions of the DSM (DSM-III and DSM-III-R) in the United States, Canada, United Kingdom, Germany, and New Zealand have shown rates that vary from 1.7 to 16.1 percent (Goldman, Genel, Bezman et al., 1998). ADHD has been identified as the most common cause of referrals to child and adolescent psychiatric health services (American Psychiatric Association, 1994). Consistently, the disorder is diagnosed more frequently in males than in females (American Academy of Child and Adolescent Psychiatry, 1997a; American Psychiatric Association, 1994). Even in children rated by teachers as meeting criteria for any subtype of ADHD, fewer girls than boys receive an ADHD diagnosis (Wolraich, Hannah, Pinnock et al., 1996).

Although it was previously thought that ADHD remitted before or during adolescence, it is now estimated that more than 70 percent of hyperactive children continue to meet criteria for ADHD as adolescents and up to 65 percent as adults (Barkley, 1996; Goldman, Genel, Bezman et al., 1998).

Problems with the diagnosis and treatment of ADHD can also arise because of the presence of comorbidity, in the form of anxiety disorders, communication disorders, mood disorders, conduct disorders (CDs), oppositional defiant disorder (ODD), learning disorders, Tourette's syndrome, and subnormal intelligence (American Psychiatric Association, 1994; Goldman, Genel, Bezman et al., 1998; Orford, 1998). In fact, it has been estimated that as many as 65 percent of children with ADHD have at least one comorbid disorder (Goldman, Genel, Bezman et al., 1998). ADHD with comorbid oppositional defiant and/or conduct disorder is the most prevalent comorbidity. Children with ADHD and comorbid ODD/CD are more likely to be males, live in families with higher rates of psychosocial adversity, and have a poorer prognosis characterized by antisocial behavior, substance use disorder, and poor scholastic success. ADHD with ODD/CD may represent a genetic subtype (Biederman, Faraone, and Keenan, 1992; Cadoret and Stewart, 1991). However, the evidence for differential response to medication of ADHD with and without comorbid ODD/CD is not strong (Barkley, McMurray, Edelbrock et al., 1989). Children with comorbid CD may be less likely to comply with treatment regimens. Similarly, their families may be less adherent to treatment.

Comorbid internalizing disorders such as anxiety or depressive disorders are also common (reviewed in Jensen, Martin, and Cantwell, 1997). Few differences in clinical or demographic features have been found between ADHD with and without comorbid anxiety: ADHD in patients with anxiety is associated with more psychosocial risk factors (Biederman, Milberger, Faraone et al., 1995) and possibly with less impulsivity (Pliszka, 1992). This combination does not appear to be a distinct genetic subtype of ADHD (Biederman, Faraone, and Keenan, 1992). However, evidence shows that children with a diagnosis of ADHD with comorbid anxiety may respond less well to stimulants and better to antidepressants (Jensen, Martin, and Cantwell, 1997).

The presence of ADHD has been associated with some individual and family features. Patients have impaired academic achievement and may be rejected by peers, and their family relationships are often characterized by resentment and antagonism (American Psychiatric Association, 1994). Increased levels of parental frustration, marital discord, and divorce occur in families who have children with ADHD (NIH Consensus Statement Online, 1998). Individuals with ADHD also tend to consume a disproportionate share of resources and attention from educators, the health care system, social service agencies, and the legal system. (NIH Consensus Statement Online, 1998).

Many different treatment modalities have been proposed for patients with ADHD, including, among others, pharmacological agents (e.g., stimulants, antidepressants), cognitive/behavioral techniques, dietary interventions, and combinations of any of the above. However, given the present debate around the existence of ADHD, the variation in estimates of prevalence, and the frequency with which comorbid disorders are identified, it is not surprising to find wide variation and controversy around its treatment. This variability in treatments in North America led to the development of practice parameters by the American Academy of Child and Adolescent Psychiatry (AACAP) (American Academy of Child and Adolescent Psychiatry, 1997b) and has motivated the American Academy of Pediatrics (AAP) to develop clinical practice guidelines. The APA is currently contemplating how to use the available information, including this report, in the development of quality improvement projects.