Attention-Deficit/Hyperactivity Disorder

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Chapter 30 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 the most extensively studied mental disorder 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 30-1). Definitions vary in different countries (Table 30-2). Affected children commonly 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 30-3).

Table 30-1 DSM-IV DIAGNOSTIC CRITERIA FOR ATTENTION-DEFICIT/HYPERACTIVITY DISORDER

A Either 1 or 2

CODE BASED ON TYPE

Reprinted with permission from American Psychiatric Association: Diagnostic and statistical manual of mental disorders, fourth edition, text revision, Washington, DC, 2000, American Psychiatric Association. Copyright 2000 American Psychiatric Association.

Table 30-2 DIFFERENCES BETWEEN U.S. AND EUROPEAN CRITERIA FOR ADHD OR HKD

DSM-IV ADHD ICD-10 HKD
SYMPTOMS
Either or both of following:

All of following:

PERVASIVENESS
Some impairment from symptoms is present in >1 setting Criteria are met for >1 setting

ADHD, attention-deficit/hyperactivity disorder; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders, 4th edition; HKD, hyperkinetic disorder; ICD-10, International Classification of Diseases, 10th edition.

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

Table 30-3 DIFFERENTIAL DIAGNOSIS OF ATTENTION-DEFICIT/HYPERACTIVITY DISORDER

PSYCHOSOCIAL FACTORS

DIAGNOSES ASSOCIATED WITH ADHD BEHAVIORS

MEDICAL AND NEUROLOGIC CONDITIONS

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.

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.

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 and alcohol use during pregnancy and prenatal or postnatal exposure to lead are commonly linked to attentional difficulties associated with the development of ADHD. Food colorings and preservatives have inconsistently been associated with hyperactivity in previously hyperactive children.

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.

Abnormal brain structures are linked to an increased risk of ADHD; 20% of children with severe traumatic brain injury are reported to have subsequent onset of substantial symptoms of impulsivity and inattention. Children with head or other injury and in whom ADHD is later diagnosed might have impaired balance or impulsive behavior as part of the ADHD, thus predisposing them to injury. Structural (functional) abnormalities have been identified in children with ADHD without pre-existing identifiable brain injury. 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.

Psychosocial family stressors can also contribute to or exacerbate the symptoms of ADHD.

Epidemiology

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