Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common neurobiologic disorder characterized by developmentally inappropriate levels of inattention, hyperactivity, and impulsivity. ADHD also is one of the most prevalent chronic health conditions affecting school-age children. Consequently, physicians frequently are asked to evaluate children for a possible diagnosis of ADHD. The importance of an appropriate and timely diagnosis is based on the knowledge that children who have ADHD may experience difficulty in social, emotional, and academic domains and that treatment can improve outcomes for these children.ADHD is a behavioral disorder, making it difficult to quantify. Epidemiologic studies indicate that at least 3% of children in the United States are affected by ADHD, with usual quoted rates of 5% and 8%. (1) Prevalence rates for ADHD vary, depending on the patient sample, geography, and diagnostic criteria (Table 1). The diagnosis is reported 2.5 times more frequently in boys than in girls, with 9.2% of males and 2.9% of females found to have behaviors that are consistent with ADHD. ADHD is considered a lifelong condition. Among adolescents who receive ADHD diagnoses as children, 60% to 80% continue to meet criteria for ADHD during their teenage years and adulthood.Prevalence rates for ADHD vary by age. Studies indicate that school-age children are more likely to be diagnosed compared with preschool-age children and adolescents. Approximately 50% of children who receive the diagnosis are treated with medication. According to a 2003 National Survey of Children's Health, 56.3% of children who had reported ADHD were being treated with medication at the time of the survey, and school-age children were most likely to be receiving medication for ADHD. (2)Studies have not demonstrated a consistent association among ADHD prevalence and race, ethnicity, or socioeconomic status. However, environmental and biologic factors may increase the risk of ADHD. Environmental factors include early lead exposure and prenatal exposure to cigarette smoking and alcohol. Biologic factors such as low birthweight, prematurity, and intrauterine growth restriction also increase the risk for ADHD.Research in the fields of neurobiology, genetics, and neuropsychology support a biologic basis for ADHD. Many studies show an association between ADHD and biologic systems that are believed to control attention and regulate inhibition. However, no single cause of ADHD has been identifiedNeuroimaging studies have shown structural and functional differences in areas of the brains in patients who have ADHD compared with patients who have no ADHD. Certain regions of the brain, rich in dopaminergic and noradrenergic pathways and associated with executive function, seem to be particularly affected, including the prefrontal cortex, striatum, and cerebellum. Functional magnetic resonance imaging (MRI) studies suggest that these particular regions of the brain are less activated in children who have ADHD compared with those of age-matched controls during activities that measure executive function, a cognitive process of the frontal lobe that is used to solve problems or achieve a goal. Other studies, using brain MRI, have found reductions in prefrontal, frontal, and hemispheric volumes in individuals who have ADHD compared with controls. The clinical significance of these differences is not clear.Several studies support the hypothesis that ADHD is associated with deficits in executive functioning. Studies based on results from neuropsychological tests of executive function in children who have ADHD showed that these children performed poorly compared with age-matched controls on specific tasks. Although these results improve understanding of the cognitive problems that some children who have ADHD may face, the results do not provide adequate evidence to conclude that problems with executive function are specific to ADHD. However, executive function deficits may be a comorbid problem among children who have ADHD. Tests of executive function, such as set shifting, working memory, or processing speed, and other neuropsychological tests, such as continuous performance testing, should not be used alone to diagnose ADHD. (3)Genetic studies suggest that ADHD is an inherited disorder. ADHD is more likely if a parent or sibling has been diagnosed with the disorder. This conclusion is supported by the high concordance for ADHD in identical twins as well as by family studies. Multiple genes contribute to the ADHD phenotype, including those related to monoaminergic (dopaminergic, serotonergic, and noradrenergic) neurotransmission. These genes include dopamine receptor genes (DRD4 and DRD5) and a dopamine transporter gene (DAT1). The basis for these studies emerged from evidence indicating that these neurotransmitters are involved in the modulation of attention and behavioral regulation in the frontal cortex. Despite the increased prevalence in male children, no study has shown that ADHD is attributable to an X-linked effect.ADHD is defined as a mental health disorder in the Diagnostic and Statistical Manual 4th Edition (DSM IV). (4) Over the years, the diagnostic criteria have been revised as clinical impressions of what constitutes this disorder have shifted. The most current definition of ADHD is listed under DSM IV criteria as “a persistent pattern of inattention and/or hyperactivity-impulsivity that is more frequent and severe than is typically observed in individuals of comparable levels of development.” The DSM IV criteria were developed by a committee and were based on a review of the literature and an analysis of field trials to determine whether the symptoms of ADHD had diagnostic utility. This effort led to the development of the two broad categories of symptoms (inattention and hyperactivity/impulsivity) and the distinction of three subtypes of ADHD (predominantly inattentive, predominantly hyperactive/impulsive, and combined type) (Table 1). To meet criteria for the predominantly inattentive subtype, the child must exhibit six of nine symptoms from A1. To meet criteria for the predominantly hyperactive subtype, the child must exhibit six of nine symptoms from category A2. To meet criteria for the combined type, the child must exhibit six of nine symptoms from both categories.ADHD is a behavioral disorder. Diagnosis requires a comprehensive clinical evaluation based on identifying children who have the core symptoms of inattention, hyperactivity, and impulsivity and whose behavior is sufficiently severe and persistent to cause functional impairment. No single test is available to establish the diagnosis. Although many children may be inattentive, hyperactive, or impulsive, the level of severity and degree of functional impairment, as well as considerations of what else might be causing the symptoms, determine which children meet the diagnosis and are treated for ADHD.To assist clinicians with the accurate identification of children who have ADHD, the American Academy of Pediatrics (AAP) published a clinical practice guideline in 2000. (5) This guideline specifically urges primary care physicians to initiate an evaluation for ADHD in “any child, ages 6 to 12, who presents with the core symptoms of ADHD, behavior problems or academic difficulties.” In addition, the guideline specifies that: The initial evaluation for suspected ADHD may be prompted by a variety of clinical circumstances. A clinician may become concerned about ADHD during a routine health supervision visit after screening for behavior and emotional problems. More frequently, parents, teachers, caregivers, or other professionals may raise concerns independent of any health-care screening effort. For example, parents may be concerned about their child's declining academic performance, relationship difficulties with peers or family members, or symptoms of emotional problems.Once a concern is identified, an initial screening begins by obtaining a description of the child's behavior and its impact on his or her ability to function in school, at home, and with peers. During the screening process, it should be determined if evidence is sufficient to proceed with an additional evaluation for ADHD. Useful questions at this point should address the child's academic performance, homework completion, behavioral or mood problems, and peer relationships.While gathering information, the clinician should be aware that the presenting symptoms of ADHD vary with the age and developmental level of the child. For example, during the preschool years, many children are inattentive, hyperactive, or impulsive. It may be difficult to distinguish age-appropriate levels of physical activity and short attention span from those activity levels and attention spans in children who have ADHD. Although the AAP guideline does not include specific recommendations regarding the diagnosis of ADHD in this population, studies show that preschool-age children may have significant attention or behavioral problems consistent with a diagnosis of ADHD. However, among preschool-age children who receive the diagnosis of ADHD, fewer than 50% continue to have the diagnosis during childhood. The degree, duration, and pervasiveness of ADHD symptoms help to distinguish those children who are most likely to develop a persistent pattern of behavior that is consistent with ADHD.As children enter elementary school, activity levels decline and children are expected to sustain attention for longer periods of time, to complete tasks independently, and to work cooperatively with their peers. At this age, children typically are able to focus for longer periods of time but may be impulsive at times. Teachers and parents of children who have underlying ADHD may express concerns about the child's safety or his or her ability to remain focused in class or to follow school routines.During adolescence, demands are greater for organizational skills, time management, and the mastering of large amounts of material. Some adolescents who have ADHD, especially the predominately inattentive type, may not receive a diagnosis until middle school or high school. If there are not signs of significant impairment in functioning, a diagnosis of ADHD cannot be made. However, a diagnosis of ADHD still should be considered if an undiagnosed adolescent manifesting previous symptoms becomes more disruptive in class, exhibits increased academic problems, engages in increased risk-taking behavior, or becomes oppositional as the academic and maturational challenges increase.If the history indicates that a child's behavior is contributing to significant impairment in more than one setting, the clinician may proceed with the diagnostic process. Specific information about the child's symptoms to determine if they meet DSM IV criteria for ADHD must be obtained and whether another cause might better explain the symptoms must be determined. Both the parent and child should be interviewed to determine information about the child's behavior as well as the onset, duration, and severity of symptoms and the context in which the symptoms occur. For example, the clinician may inquire about the child's behavior in various situations: completing homework assignments and long-term school projects, getting ready for school in the morning, relating to peers, sitting in class, or following instructions. In cases where the presenting symptoms of inattention, hyperactivity, or impulsivity do not meet criteria for ADHD but warrant additional behavioral interventions or parent education, the clinician can use the Diagnostic and Statistical Manual for Primary Care (DSM-PC) (6) to document the child's behavior in the medical record and to develop an intervention plan.The medical record should contain specific descriptions of the child's symptoms and not simply state that the child is inattentive, hyperactive, or impulsive. For example, the description of a hyperactive middle school child may indicate that the child leaves his seat during class, runs out of the classroom, fidgets endlessly, or has difficulty sitting still during any activity that requires concentration.Because the DSM-IV symptoms were not selected scientifically and because there is substantial overlap among the symptoms, it is harder to establish a rating scale or a scientific scoring to determine whether a specific child has ADHD. Therefore, ADHD-specific rating scales are not diagnostic. However, they may be used to gather information about the child's behaviors from the parent, teacher, or both. In general, these rating scales assess the core symptoms of ADHD, as specified in the DSM IV, and they are relatively easy to administer (Table 2). The strength of the rating scales lies in their link to DSM IV symptoms. Rating scales probably are most useful in documenting whether the rater sees the core symptoms as being present for a specific child compared with his or her same-age peers. Broad-band rating scales that are not ADHD-specific have not been shown to provide sufficient evidence to support their use in the assessment of ADHD. 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