ADHD is multifactorial in origin, with genetic, neural, and environmental contributions. Twin studies and family studies demonstrate high heritability (0.8) and greater risk of developing ADHD in first-degree relatives. Candidate genes include those involving the dopaminergic and noradrenergic neurotransmitter systems. Neuroimaging studies (functional magnetic resonance imaging and positron emission tomography, commonly recognized as fMRI and PET, respectively) have shown structural and functional differences, particularly of the frontal lobes, inferior parietal cortex, basal ganglia, corpus callus, and cerebellar vermis. Prenatal exposure to substances (e.g., nicotine, alcohol) and damage to the central nervous system from trauma or infection increase the risk of ADHD.
U.S. prevalence rates for ADHD vary, depending on criteria used and population studied, with rates typically in the 5% to 10% range. The male to female ratio is 2 to 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, persist into adolescence and adulthood in 60% to 80% of patients.
ADHD is diagnosed clinically by history. Open-ended questions should focus on specific behaviors and their impact on academic performance, family and peer relationships, safety, self-esteem, and daily activities. Information should be gathered from the family and the school via ADHD-specific rating scales such as the Conners’ Rating Scales or the Vanderbilt Rating Scales.
A physical examination is essential to identify medical(e.g., neurologic, genetic) or developmental problems (e.g.,cognitive impairment, language disorder, learning disability, autism spectrum disorder) that may underlie, coexist,or provide an alternative explanation for the child’s behaviors. Observation of the child, the parents, and their interactions is part of the evaluation. Keep in mind that childrenwith ADHD can typically focus without hyperactivity in environments with low stimulation and little distraction (e.g., clinician’s office).
Laboratory and imaging studies are not routinely recommended but may help exclude other conditions. Consider thyroid function studies, blood lead levels, genetic studies, and brain imaging studies if indicated by medical history, environmental history, or physical examination.
The clinician should first consider the child’s developmental level to determine whether the behaviors are within the range of normal. Medical conditions, such as sleep disordered breathing, seizure disorders, substance use, hyperthyroidism, lead intoxication, and sensory deficits, should beconsidered as possible causes for a child’s hyperactivity anddistractibility. Inattention and hyperactivity may be presentas features of genetic disorders such as fragile X, 22q11.2deletion syndrome, and neurofibromatosis 1. Chaotic living situations or psychological stress (e.g., bullying, abuse)can also lead to symptoms of hyperactivity, impulsivity, andinattention. Children who have symptoms of ADHD in onlyone setting may be having problems due to cognitive level,level of emotional maturity, or feelings of well-being in thatsetting.
More important, coexisting conditions are present in up to 60% of children with ADHD. These include psychiatric conditions, particularly oppositional defiant disorder, conduct disorder, anxiety disorder, and depression; learning disabilities; language disorders; and tic disorders. These conditions are also part of the differential diagnosis of ADHD.
Management begins with recognizing ADHD as a chronic condition and educating affected children and their parents about the diagnosis, treatment options, and prognosis.
Table 13-1 FDA-Approved Medications for Attention-Deficit/Hyperactivity Disorder GENERIC MEDICATION BRAND NAME INITIAL-MAXIMUM DOSE DURATION (h) STIMULANTS Mixed amphetamine salts Adderall* Adderall XR* 2.5 mg–40 mg 5 mg–40 mg 6 10