Disease State

ADHD is characterized by: (1) the inattentive; (2) the hyperactive/impulsive (hyperactivity without inattention); or (3) the combined type.1 The condition arises before the age of 7 and frequently persists through adolescence and into adulthood, although the behavioral features of the condition vary at different ages. Children with the hyperactive/ impulsive subtype usually develop symptoms of ADHD by 4 years of age, with significant difficulties contributing to academic challenges by the age of 8. In contrast, children with the inattentive subtype tend to develop difficulties later, with a typical age of presenting with noticeable difficulties around 9-10 years of age. In adolescence, the hyperactive and impulsive symptoms may become less evident, but the problems with inattention often persist. Generally ADHD is assumed to have a ratio of 10:1 (boys to girls) based on clinical estimates, while community estimates are 3:1. In adult samples, the ratios of men to women are approximately equal.

ADHD, defined by the American Psychiatric Association Diagnostic and Statiscal Manital-lV (DSM-IV), is diagnosed using behavioral criteria. Behavioral heterogeneity among ADHD sufferers complicates the diagnosis and makes it difficult to establish its prevalence. ADHD prevalence is typically estimated at 4-12% of school-aged children.3 One of the difficulties in estimating the prevalence of ADHD is that, unlike for other psychiatric disorders, physicians rely on recognition of various types of behaviors in different combinations (somewhat subjective judgment) for diagnosis. More than 4.5 million individuals have been diagnosed with ADHD in the US, the vast majority of whom are males between 5 and 19 years of age. Studies have suggested that 30-50% of children with ADHD continue to have symptoms of the disorder into adulthood, although a smaller proportion of 10% have clinically significant symptoms. This suggests that 1-3% of adults may suffer ADHD symptoms, and are likely deserving treatment. The negative social and occupational impact of ADHD in adults is now recognized, with prevalence in adulthood estimated at 1-3%. The recognition of distinct subtypes of ADHD, particularly the inattentive subtype, in more recent definitions of ADHD has resulted in increased prevalence estimates. Moreover, inattentive behavior is hypothesized to be more prevalent in girls, who are generally viewed as being underdiagnosed for ADHD.

It can be difficult to estimate worldwide prevalence rates, as not all countries use the DSM-IV ADHD criteria. In Europe, DSM-IV criteria are not routinely used for diagnosis (the International Classification of Disease manual (ICD-10) is used), leading to a much lower rate of diagnosis and a more severe population being treated. In Japan, ADHD is virtually nonexistent and this is not expected to change in the midterm. When operational definitions of ADHD are used, studies of children aged 4-16 years old were found to have the following frequencies: New Zealand 7%, US 8%, Canada 6%, Puerto Rico 9%, UK 5%, and Hong Kong 9%. When ICD-10 psychiatric diagnosis criteria are applied, the following frequencies were found: Sweden, 2%; Germany 2-4%; UK 2%; and Hong Kong 1%.4 Studies in Brazil have estimated an ADHD prevalence of 5.8%.5

In the US, ADHD is the commonest neurobehavioral disorder of childhood and is among the most prevalent chronic health conditions affecting school-aged children. ADHD accounts for 30-50% of all referrals for child mental health services in the US,1 and comprises the majority of the economic cost of childhood mental disorders. Recent projections from the US Census Bureau indicate that the school age population is growing by approximately 300 000 per year. By 2010, the number of children under 19 years of age will have grown from 78.5 million in 2000 to 81 million. Assuming the mean prevalence of 6%, the incidence of pediatric ADHD will be approximately 4.8 million. In addition, most physicians do not consider hyperactivity to be a stand-alone disorder. As many as one-third of children diagnosed with ADHD have at least one coexisting condition - oppositional defiant disorder (35.2%), conduct disorder (25.7%), anxiety disorder (25.8%), and/or depression (18.2%).2 Although it is generally accepted that ADHD persists into adulthood, there is a noticeable lack of a consensus as to diagnostic criteria suitable for adults with ADHD. As children approach adulthood, a number of developmental changes occur, and diagnostic criteria are not currently identifying how the subtypes change in this transition period. Furthermore, adult diagnostic criteria currently rely on symptomology identified in younger populations, and likely do not adequately capture all of the adults with ADHD. In general, there are three approaches for diagnosing adult ADHD: (1) the Wender Utah criteria; (2) the DSM-IV criteria; and (3) laboratory assessments.6

In the 1970s-80s evidence emerged suggesting that ADHD persisted into adulthood. At the same time the diagnostic framework for the DSM-III was developed, focusing on childhood hyperactivity. The Wender Utah diagnostic criteria were developed based on the premise that diagnostic criteria appropriate for children were not appropriate for adults and include a retrospective childhood diagnosis, ongoing difficulties with inattentiveness and hyperactivity, and the inclusion of two other core symptoms of adult ADHD. As detailed by McGough and Barkley in 2004,6 while the Utah approach to adult ADHD underscores the importance of retrospective childhood diagnosis and evaluation of current symptoms, the Wender Utah diagnostic criteria do not identify patients with predominantly inattentive symptoms, exclude some patients with comorbid psychopathology, and differ from the DSM diagnostic framework.6

The following general categories are used for ADHD diagnosis using DSM-IV criteria:

• the presence of six or more symptoms for at least 6 months

• demonstration of clinically significant impairment in social, academic, or occupational functioning

• observation of symptoms in two or more settings

• onset of symptoms before the age of 7 years

• the exclusion of other disorders.

Although the potential areas of impairment include occupational functioning, the DSM-IV focuses largely on children. As an example, in discussing possible symptoms, these tend to focus on examples such as 'cannot play quietly' or 'runs and climbs excessively' - items clearly missing the areas of dysfunction pertinent to adults and lacking face validity for adults. One of the difficulties with both the Wender Utah scale and the DSM-IV criteria are that they require a diagnosis of ADHD in childhood. If the physician does not examine the patient until adulthood, this requires anecdotal recall, which is often unreliable. Although the DSM-IV criteria have been used (successfully) in diagnosing adult ADHD, the scale is likely not the most appropriate for diagnosing adults. Other scales that have been validated include the Adult Self-Report Scale (ASRS), developed in conjunction with the World Health Organization,95 and the Conners Adult ADHD Rating Scale (CAARS), comprised of self-reports and observer ratings, and providing normative data for comparison.

Other diagnostic criteria that have been proposed include laboratory-based diagnostic paradigms such as tests of executive functioning and working memory,7 ecological measures of academic performance and classroom behavior,8 the CPT,9 electroencephalography,10 and neuroimaging.11 Obviously there is interest in the development of laboratory tests for ADHD, as research as well as diagnostic criteria. The other advantage of laboratory tests is the correlation with animal models. For example, the CPT is hypothesized to have similarities with the 5-CSRTT discussed under animal models. To date, however, there is a lack of data supporting the use of these measures as diagnostic tools.6

While not yet appropriate for diagnosing ADHD, the development of laboratory tests is positively influencing other areas for future research, including efforts directed toward understanding the heterogeneity of ADHD. Studies investigating the underlying neurobiology should lead to new understanding in this area. Imaging techniques are giving important insight, and this should ultimately contribute to a greater knowledge of the disorder. Pharmacogenomic studies are in their infancy, although the National Human Genome Research Institute is currently sponsoring a study on the genetic analysis of ADHD.

Future research will also need to consider a full range of medications, disease manifestations, and pharmacokinetic criteria. Associated comorbidities with ADHD are poorly understood, and need to be clearly identified. A recently published practice parameter discussed the use of stimulant medications in the treatment of children, adolescents, and adults, and summarized limited studies investigating the combination of stimulants and other psychotropic agents useful for treating comorbid conditions,12 suggesting this as a key area for future research.

ADHD Secrets Uncovered

ADHD Secrets Uncovered

Announcing an important message for parents. Has Your Child Been Diagnosed With ADHD Is Coping With Your Child's Behavior Wearing You Out Are You Tired of Searching For Answers

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