Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioral disorder of childhood, among the most prevalent chronic health conditions affecting school-aged children, and one of the most extensively studied neurodevelopmental disorders of childhood. ADHD is characterized by inattention, including increased distractibility and difficulty sustaining attention; poor impulse control and decreased self-inhibitory capacity; and motor overactivity and motor restlessness ( Table 49.1 and Fig. 49.1 ). Definitions vary in different countries ( Table 49.2 ). Affected children usually experience academic underachievement, problems with interpersonal relationships with family members and peers, and low self-esteem. ADHD often co-occurs with other emotional, behavioral, language, and learning disorders ( Table 49.3 ). Evidence also suggests that for many people, the disorder continues with varying manifestations across the life cycle, leading to significant under- and unemployment, social dysfunction and increased risk of antisocial behaviors (e.g., substance abuse), difficulty maintaining relationships, encounters with the law, death from suicide, and, if untreated, accidents ( Figs. 49.2 and 49.3 ).

Table 49.1

DSM-5 Diagnostic Criteria for Attention-Deficit/Hyperactivity Disorder (ADHD)

A
A persistent pattern of inattention and/or hyperactivity/impulsivity that interferes with functioning or development, as characterized by (1) and/or (2):
- 1
  Inattention: Six (or more) of the following symptoms of inattention have persisted for ≥6 mo to a degree that is inconsistent with development level and that negatively impacts directly on social and academic/occupational activities:
  - a
    Often fails to give close attention to details or makes careless mistakes in schoolwork, at work, or during other activities (e.g., overlooks or misses details, work is inaccurate).
  - b
    Often has difficulty sustaining attention in tasks or play activities.
  - c
    Often does not seem to listen when spoken to directly.
  - d
    Often does not follow through on instructions and fails to finish schoolwork, chores, or duties in the workplace (not due to oppositional behavior or failure to understand instructions).
  - e
    Often has difficulty organizing tasks and activities.
  - f
    Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (e.g., schoolwork, homework).
  - g
    Often loses things necessary for tasks or activities (e.g., toys, school assignments, pencils, books, tools).
  - h
    Is often easily distracted by extraneous stimuli.
  - i
    Is often forgetful in daily activities.
- 2
  Hyperactivity/impulsivity: Six (or more) of the following symptoms of inattention have persisted for ≥6 mo to a degree that is inconsistent with development level and that negatively impacts directly on social and academic/occupational activities.
  - a
    Often fidgets with hands or feet or squirms in seat.
  - b
    Often leaves seat in classroom or in other situations in which remaining seated is expected.
  - c
    Often runs about or climbs excessively in situations in which it is inappropriate (in adolescents or adults, may be limited to subjective feelings of restlessness).
  - d
    Often has difficulty playing or engaging in leisure activities quietly.
  - e
    Is often “on the go” or often acts as if “driven by a motor.”
  - f
    Often talks excessively.
    
    Impulsivity.
  - g
    Often blurts out answers before questions have been completed.
  - h
    Often has difficulty awaiting turn.
  - i
    Often interrupts or intrudes on others (e.g., butts into conversations or games).
B
Several inattentive or hyperactive/impulsive symptoms were present before 12 yr of age.
C
Several inattentive or hyperactive/impulsive symptoms are present in 2 or more settings (e.g., at school [or work] or at home) and is documented independently.
D
There is clear evidence of clinically significant impairment in social, academic, or occupational functioning.
E
Symptoms do not occur exclusively during the course of schizophrenia, or another psychotic disorder, and are not better accounted for by another mental disorder (e.g., mood disorder, anxiety disorder, dissociative disorder, personality disorder, substance intoxication or withdrawal).

Code Based on Type

314.01 Attention-deficit/hyperactivity disorder, combined presentation: if both Criteria A1 and A2 are met for the past 6 mo.
314.00 Attention-deficit/hyperactivity disorder, predominantly inattentive presentation: if Criterion A1 is met but Criterion A2 is not met for the past 6 mo.
314.01 Attention-deficit/hyperactivity disorder, predominantly hyperactive-impulsive presentation: if Criterion A2 is met but Criterion A1 is not met for the past 6 mo.
Specify if:
- Mild: Few, if any, symptoms in excess of those required to make the diagnosis are present, and if the symptoms result in no more than minor impairments in social and occupational functioning.
- Moderate: Symptoms or functional impairment between “mild” and “severe” are present.
- Severe: Many symptoms in excess of those required to make the diagnosis, or several symptoms that are particularly severe, are present, or the symptoms result in marked impairment in social or occupational functioning.

Table 49.2

Differences Between U.S. and European Criteria for ADHD or HKD

From Biederman J, Faraone S: Attention-deficit hyperactivity disorder, Lancet 366:237–248, 2005.

DSM-5 ADHD	ICD-10 HKD
SYMPTOMS
Either or both of the following: At least 6 of 9 inattentive symptoms At least 6 of 9 hyperactive or impulsive symptoms	All of the following: At least 6 of 8 inattentive symptoms At least 3 of 5 hyperactive symptoms At least 1 of 4 impulsive symptoms
PERVASIVENESS
Some impairment from symptoms is present in >1 setting	Criteria are met for >1 setting

ADHD, Attention-deficit/hyperactivity disorder; HKD, hyperkinetic disorder; DSM-5, Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition ; ICD-10, International Classification of Diseases, Tenth Edition .

Table 49.3

From Reiff MI, Stein MT: Attention-deficit/hyperactivity disorder evaluation and diagnosis: a practical approach in office practice, Pediatr Clin North Am 50:1019–1048, 2003. Adapted from Reiff MI: Attention-deficit/hyperactivity disorders. In Bergman AB, editor: 20 Common problems in pediatrics, New York, 2001, McGraw-Hill, p 273.

Differential Diagnosis of Attention-Deficit/Hyperactivity Disorder (ADHD)

Psychosocial Factors

Response to physical or sexual abuse
Response to inappropriate parenting practices
Response to parental psychopathology
Response to acculturation
Response to inappropriate classroom setting

Diagnoses Associated With ADHD Behaviors

Fragile X syndrome
Fetal alcohol syndrome
Pervasive developmental disorders
Obsessive-compulsive disorder
Gilles de la Tourette syndrome
Attachment disorder with mixed emotions and conduct

Medical and Neurologic Conditions

Thyroid disorders (including general resistance to thyroid hormone)
Heavy metal poisoning (including lead)
Adverse effects of medications
Effects of abused substances
Sensory deficits (hearing and vision)
Auditory and visual processing disorders
Neurodegenerative disorder, especially leukodystrophies
Posttraumatic head injury
Postencephalitic disorder

Note: Coexisting conditions with possible ADHD presentation include oppositional defiant disorder, anxiety disorders, conduct disorder, depressive disorders, learning disorders, and language disorders. Presence of one or more of the symptoms of these disorders can fall within the spectrum of normal behavior, whereas a range of these symptoms may be problematic but fall short of meeting the full criteria for the disorder.

Etiology

No single factor determines the expression of ADHD; ADHD may be a final common pathway for a variety of complex brain developmental processes. Mothers of children with ADHD are more likely to experience birth complications, such as toxemia, lengthy labor, and complicated delivery. Maternal drug use has also been identified as a risk factor in the development of ADHD. Maternal smoking, alcohol use during pregnancy, and prenatal or postnatal exposure to lead are frequently linked to the attentional difficulties associated with development of ADHD, but less clearly to hyperactivity. Food coloring and preservatives have inconsistently been associated with increased hyperactivity in children with ADHD.

There is a strong genetic component to ADHD. Genetic studies have primarily implicated 2 candidate genes, the dopamine transporter gene (DAT1) and a particular form of the dopamine 4 receptor gene (DRD4), in the development of ADHD. Additional genes that might contribute to ADHD include DOCK2, associated with a pericentric inversion 46N inv(3)(p14:q21) involved in cytokine regulation; a sodium-hydrogen exchange gene; and DRD5, SLC6A3, DBH, SNAP25, SLC6A4, and HTR1B.

Structural and functional abnormalities of the brain have been identified in children with ADHD. These include dysregulation of the frontal subcortical circuits, small cortical volumes in this region, widespread small-volume reduction throughout the brain, and abnormalities of the cerebellum, particularly midline/vermian elements (see Pathogenesis ). Brain injury also increases the risk of ADHD. For example, 20% of children with severe traumatic brain injury are reported to have subsequent onset of substantial symptoms of impulsivity and inattention. However, ADHD may also increase the risk of traumatic brain injury.

Psychosocial family stressors can also contribute to or exacerbate the symptoms of ADHD, including poverty, exposure to violence, and undernutrition or malnutrition.

Epidemiology

Studies of the prevalence of ADHD worldwide have generally reported that 5–10% of school-age children are affected, although rates vary considerably by country, perhaps in part because of differing sampling and testing techniques. Rates may be higher if symptoms (inattention, impulsivity, hyperactivity) are considered in the absence of functional impairment. The prevalence rate in adolescent samples is 2–6%. Approximately 2% of adults meet criteria for ADHD. ADHD is often underdiagnosed in children and adolescents. Youth with ADHD are often undertreated with respect to what is known about the needed and appropriate doses of medications. Many children with ADHD also present with comorbid neuropsychiatric diagnoses, including oppositional defiant disorder, conduct disorder, learning disabilities, and anxiety disorders. The incidence of ADHD appears increased in children with neurologic disorders such as the epilepsies, neurofibromatosis, and tuberous sclerosis (see Table 49.3 ).

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