Attention-Deficit Disorders
ATTENTION-DEFICIT/HYPERACTIVITY DISORDER
Attention-deficit/hyperactivity disorder (ADHD) is characterized by a pattern of diminished sustained attention and higher levels of impulsivity in a child or adolescent than expected for someone of that age and developmental level. Whereas in the past, hyperactivity was believed to be the underlying impairing symptom in this disorder, the current consensus is that hyperactivity is often secondary to poor impulse control. Impulsivity and hyperactivity share one dimension in today’s diagnostic criteria for ADHD. The diagnosis of ADHD is based on the consensus of experts that three observable subtypes—inattentive, hyperactive/impulsive, and combined—are all manifestations of the same disorder. To meet the criteria for the diagnosis of ADHD, some symptoms must be present before the age of 7 years, although ADHD is not diagnosed in many children until they are older than 7 years when their behaviors cause problems in school and other places. To confirm a diagnosis of ADHD, impairment from inattention and/or hyperactivity-impulsivity must be observable in at least two settings and interfere with developmentally appropriate functioning socially, academically, or in extracurricular activities. ADHD is not diagnosed when symptoms occur in a child, adolescent, or adult with a pervasive developmental disorder, schizophrenia, or other psychotic disorder.
Epidemiology
Reports on the incidence of ADHD in the United States have varied from 2 to 20 percent of grade-school children. A conservative figure is about 3 to 7 percent of prepubertal elementary school children. In Great Britain a lower incidence is reported than in the United States, less than 1 percent. ADHD is more prevalent in boys than in girls, with the ratio ranging from 2:1 to as much as 9:1. First-degree biological relatives (e.g., siblings of probands with ADHD) are at high risk to develop it as well as to develop other disorders, including disruptive behavior disorders, anxiety disorders, and depressive disorders. Siblings of children with ADHD are also at higher risk than the general population to have learning disorders and academic difficulties. The parents of children with ADHD show an increased incidence of hyperkinesis, sociopathy, alcohol use disorders, and conversion disorder. Symptoms of ADHD are often present by age 3 years, but the diagnosis is generally not made until the child is in a structured school setting, such as preschool or kindergarten, when teacher information is available comparing the attention and impulsivity of the child in question with peers of the same age.
Etiology
Genetic Factors.
Evidence for a genetic contribution to the emergence of ADHD includes greater concordance in monozygotic than in dizygotic twins. In addition, siblings of hyperactive children have about twice the risk of having the disorder as those in the general population. One sibling may have predominantly hyperactivity symptoms, and others may have predominantly inattention symptoms. Biological parents of children with the disorder have a higher risk for ADHD than adoptive parents. Children with ADHD are at higher risk of developing conduct disorders, and alcohol use disorders and antisocial personality disorder are more common in their parents than in the general population.
Developmental Factors.
Reports in the literature state that September is the peak month for births of children with ADHD with and without comorbid learning disorders. The implication is that prenatal exposure to winter infections during the first trimester may contribute to the emergence of ADHD symptoms in some susceptible children.
BRAIN DAMAGE.
It has been speculated that some children affected by ADHD had subtle damage to the central nervous system (CNS) and brain development during their fetal and perinatal periods. The hypothesized brain damage may potentially be associated with circulatory, toxic, metabolic, mechanical, or physical insult to the brain during early infancy caused by infection, inflammation, and trauma. Children with ADHD exhibit nonfocal (soft) neurological signs at higher rates than those in the general population.
Neurochemical Factors.
Many neurotransmitters have been associated with ADHD symptoms. Animal studies have shown that the locus ceruleus, consisting of mainly noradrenergic neurons, plays a major role in attention. The noradrenergic system consists of the central system (originating in the locus ceruleus) and the peripheral sympathetic system. The peripheral noradrenergic system may be of more importance in ADHD. Thus, a dysfunction in peripheral epinephrine, which causes the hormone to accumulate peripherally, could potentially feed back to the central system and “reset” the locus ceruleus to a lower level. In part, hypotheses about the neurochemistry of the disorder have arisen from the impact of many medications that exert a positive effect on it. The most widely studied drugs in the treatment of ADHD—the stimulants—affect both dopamine and norepinephrine, leading to neurotransmitter hypotheses that include possible dysfunction in both the adrenergic and the dopaminergic systems. Stimulants increase catecholamine concentrations by promoting their release and blocking their uptake. Stimulants and some tricyclic drugs—for example, desipramine (Norpramin)—reduce levels of urinary 3-methoxy-4-hydroxyphenylglycol, a metabolite of norepinephrine. Clonidine (Catapres), a norepinephrine agonist, has been helpful in treating hyperactivity. Other drugs that have reduced hyperactivity include tricyclic drugs and monoamine oxidase inhibitors. Overall, no clear-cut evidence implicates a single neurotransmitter in the development of ADHD, but many neurotransmitters may be involved in the process.
Neurophysiological Factors.
The human brain normally undergoes major growth spurts at several ages: 3 to 10 months, 2 to 4 years, 6 to 8 years, 10 to 12 years, and 14 to 16 years. Some children have a maturational delay in the sequence and manifest symptoms of ADHD that appear to normalize by about age 5 years. A physiological correlate is the presence of a variety of nonspecific abnormal electroencephalogram (EEG) patterns that are disorganized and characteristic of young children. In some cases, the EEG findings normalize over time. A recent study of quantitative EEGs in children with ADHD, in children with undifferentiated attentional problems, and in normal controls indicates that both groups with attentional problems evince increased beta-band relative percentages and decreased rare tone P3000 amplitudes. Increased beta-band percentage or decreased delta-band percentage is associated with increased arousal.
Computed tomographic head scans of children with ADHD show no consistent findings. Studies using positron emission tomography (PET) have found lower cerebral blood flow and metabolic rates in the frontal lobe areas of children with ADHD than in controls. PET scans have also shown that female adolescents with the disorder have globally lower glucose metabolism than both normal control females and males with the disorder. One theory explains these findings by supposing that the frontal lobes in children with ADHD are not adequately performing their inhibitory mechanism on lower structures, an effect leading to disinhibition.
Psychosocial Factors.
Children in institutions are frequently overactive and have poor attention spans. These signs result from prolonged emotional deprivation, and they disappear when deprivational factors are removed, such as through adoption or placement in a foster home. Stressful psychic events, disruption of family equilibrium, and other anxiety-inducing factors contribute to the initiation or perpetuation of ADHD. Predisposing factors may include the child’s temperament, genetic-familial factors, and the demands of society to adhere to a routinized way of behaving and performing. Socioeconomic status does not seem to be a predisposing factor.
Diagnosis
The principal signs of inattention, impulsivity, and hyperactivity are based on a detailed history of a child’s early developmental patterns along with direct observation of the child, especially in situations that require sustained attention. Hyperactivity may be more severe in some situations (e.g., school) and less marked in others (e.g., one-on-one interviews), and it may be less obvious in pleasant structured activities (sports). The diagnosis of ADHD requires persistent, impairing symptoms of either hyperactivity/impulsivity or inattention that cause impairment in at least two different settings. For example, many children with ADHD have difficulties in school and at home. The diagnostic criteria for ADHD are outlined in Table 39-1.
Other distinguishing features of ADHD are short attention span and easy distractibility. In school, children with ADHD cannot follow instructions and often demand extra attention from their teachers. At home, they often do not comply with their parents’ requests. They act impulsively, show emotional lability, and are explosive and irritable.
Children who have hyperactivity as a predominant feature are more likely to be referred for treatment than are children with primarily symptoms of attention deficit. Children with the predominantly hyperactive-impulsive type are more likely to have a stable diagnosis over time and to have concurrent conduct disorder than are children with the predominantly inattentive type without hyperactivity. Disorders involving reading, arithmetic, language, and coordination can occur in association with ADHD. A child’s history may give clues to prenatal (including genetic), natal, and postnatal factors that may have affected the CNS structure or function. Rates of development, deviations in development, and parental reactions to significant or stressful behavioral transitions should be ascertained because they may help clinicians determine the degree to which parents have contributed or reacted to a child’s inefficiencies and dysfunctions.
School history and teachers’ reports are important in evaluating whether a child’s difficulties in learning and school behavior are primarily caused by the child’s inability to sustain attention or compromised understanding of the academic material. Additional school difficulties can result from attitudinal or maturational problems, social rejection, and poor self-image because of felt inadequacies. These reports may also reveal how the child has handled these problems. How the child has related to siblings, to peers, to adults, and to free and structured activities gives valuable diagnostic clues to the presence of ADHD and helps identify the complications of the disorder.
The mental status examination may show a secondarily depressed mood but no thought disturbance, impaired reality testing, or inappropriate affect. A child may show great distractibility, perseveration, and a concrete and literal mode of thinking. Indications of visual-perceptual, auditory-perceptual, language, or cognition problems may be present. Occasionally, evidence appears of a basic, pervasive, organically based anxiety, often referred to as body anxiety. A neurological examination may reveal visual, motor, perceptual, or auditory discriminatory immaturity or impairments without overt signs of visual or auditory acuity disorders. Children may have problems with motor coordination and difficulty copying age-appropriate figures, rapid alternating movements, right-left discrimination, ambidexterity, reflex asymmetries, and a variety of subtle nonfocal neurological signs (soft signs).
Clinicians should obtain an EEG to recognize the child with frequent bilaterally synchronous discharges resulting in short absence spells. Such a child may react in school with hyperactivity out of sheer frustration. The child with an unrecognized temporal lobe seizure focus can have a secondary behavior disorder. In these instances, several features of ADHD are often present. Identification of the focus requires an EEG obtained during drowsiness and during sleep.
Clinical Features
Attention-deficit/hyperactivity disorder can have its onset in infancy, although it is rarely recognized until a child is at least toddler age. Infants with the disorder are unduly sensitive to stimuli and are easily upset by noise, light, temperature, and other environmental changes. At times, the reverse occurs, and the children are placid and limp, sleep much of the time, and appear to develop slowly in the first months of life. More commonly, however, infants with ADHD are active in the crib, sleep little, and cry a great deal. They are far less likely than normal children to reduce their locomotor activity when their environment is structured by social limits.
In school, children with ADHD may attack a test rapidly but answer only the first two questions. They may be unable to wait to be called on in school and may respond before everyone else. At home, they cannot be put off for even a minute. Children with ADHD are often explosive or irritable. Their irritability may be set off by relatively minor stimuli, which may puzzle and dismay them. They are frequently emotionally labile and easily set off to laughter or to tears; their mood and performance are apt to be variable and unpredictable. Impulsiveness and an inability to delay gratification are characteristic. Children are often susceptible to accidents.
Table 39-1 DSM-IV-TR Diagnostic Criteria for Attention-Deficit/Hyperactivity Disorder | |||||||||||||||||||||||||||
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