Keywords
attention disorders, impulsivity, hyperactivity, stimulant, school performance
Attention-deficit/hyperactivity disorder (ADHD) is a chronic neurobehavioral disorder characterized by symptoms of inattention, hyperactivity, impulsivity, or a combination of these symptoms. It is typically diagnosed in childhood but frequently has long-term implications, including decreased likelihood of high school and postsecondary graduation as well as poor peer relations.
Etiology
ADHD is multifactorial in origin with genetic, neural, and environmental contributions. There are many studies that suggest variable degrees of genetic associations with ADHD, yet overall, clear and definitive associations are not well defined. Twin and family studies demonstrate high heritability (0.8) and greater risk of developing ADHD in first-degree relatives, especially those where ADHD persists into adolescence and adulthood. Candidate genes include those involving the dopaminergic and noradrenergic neurotransmitter systems. Neuroimaging studies (functional magnetic resonance imaging and positron emission tomography) have shown structural and functional differences, particularly of the frontal lobes, inferior parietal cortex, basal ganglia, corpus callus, and cerebellar vermis. Neuroimaging studies have demonstrated delay in cortical maturation and suggest that the pathophysiological features include large-scale neuronal networks including frontal to parietal cortical connections. Environmental links have been described with prenatal exposure to a variety of substances including nicotine, alcohol, prescription medications, and illicit substances. Environmental exposure to lead, organophosphate pesticides, or polychlorinated biphenyls has also been shown to be a risk factor. Additionally, damage to the central nervous system from trauma or infection can increase the risk of ADHD.
Epidemiology
U.S. prevalence rates for ADHD vary depending on criteria used and population studied, with approximately 11% of U.S. children diagnosed with ADHD today. The male to female ratio is 2-6:1, with greater male predominance for the hyperactive/impulsive and combined types. Girls often present with inattentive symptoms and are more likely to be underdiagnosed or to receive later diagnoses. Symptoms of ADHD, particularly impulsivity and inattention, frequently persist past childhood, with up to 80% of those affected having symptoms into adolescence, and 40% into adulthood.
Clinical Symptoms
Many of the symptoms of ADHD mimic typical findings of normal development; thus it is important to consider whether the child’s symptoms are out of proportion to what would be expected for stage of development. Symptoms of inattention (e.g., failing to pay close attention to details, appearing to not listen when spoken to directly), hyperactivity (e.g., being fidgety or restless, leaving a seat when expected to remain seated), or impulsivity (e.g., blurting out answers before a question has been completed) may indicate a diagnosis of ADHD ( Table 13.1 ).
| INATTENTIVE SYMPTOMS |
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| HYPERACTIVITY OR IMPULSIVITY SYMPTOMS |
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