Dr. Johnston of Johns Hopkins University School of Medicine and Chief Medical Officer at Kennedy Krieger Institute has no relevant financial relationships to disclose.)
This article includes discussion of attention deficit hyperactivity disorder, ADHD, and hyperkinetic syndrome. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Attention deficit hyperactivity disorder (ADHD) is the most common entity seen by child neurologists and psychiatrists. It is a neurobehavioral syndrome that is defined by its behavioral phenotype and frequently coexists with other cognitive and behavioral disorders. ADHD is a lifelong disorder. A strong familial component to ADHD exists, although it is associated with many etiologies. Genetic studies show a number of statistically significant relationships that are of small effect size. Converging data from a number of sources implicate frontal-striatal-cerebellar dysfunction as a possible mechanism for ADHD. These sources, however, fail to identify a single explanation for ADHD. Psychostimulant medications remain the mainstay of therapy, but several nonstimulant medications have been shown to be effective agents.
• ADHD is a neurologic disorder that is defined by its behavioral characteristics.
• ADHD frequently is seen in conjunction with disorders in motor, language, or academic areas.
• ADHD may persist into adulthood, and although the hyperactivity becomes attenuated, distractibility, impulsivity, and pathological disorganization may persist.
• Stimulants are the mainstay of therapy and have a wide therapeutic margin.
Historical note and terminology
Still and Tredgold are credited with the first modern descriptions of what is today known as "attention deficit hyperactivity disorder," or ADHD (Barkley 1990). They highlighted relevant features of ADHD and hypothesized a neurologic etiology. In the same era, other physicians were linking behavioral pathology to brain injuries.
In the 1930s, Strauss and colleagues described hyperactivity, distractibility, emotional lability, and perseveration in a group of survivors of encephalitis lethargica (Strauss and Lehtinen 1947). These behaviors were posited to be de facto evidence of brain injury, and it was suggested that children who demonstrated these behaviors were brain damaged, even when there was no known injury (Strauss and Kephart 1955). The minimal brain damage concept persisted until the 1960s, despite the circularity of the reasoning that led to its existence. The minimal brain damage concept gave way to the minimal brain dysfunction concept.
Ultimately, the focus shifted to the symptoms rather than etiology or mechanism. The hyperactive child syndrome was included in the Diagnostic and Statistical Manual of Mental Disorders as the hyperkinetic reaction of childhood. Inattention became the predominant feature in DSM-III; attention deficit disorder was said to exist with or without hyperactivity. The core symptoms of inattention, hyperactivity, and impulsivity were not considered 3 independent variables, and they were merged into a single syndrome that required inattention and hyperactivity-impulsivity in DSM-III-R. DSM-IV reflects the covariation of hyperactivity with impulsivity and independence of inattention. Consequently, 3 major syndromes evolved: (1) inattention and hyperactivity-impulsivity, (2) inattention alone, and (3) hyperactivity-impulsivity alone.
Some people have questioned the specificity of inattention (Halperin et al 1992). Barkley presented a model of ADHD that posits poor behavioral inhibition as the central deficit (Barkley 1997a; Barkley 1997b); this results in the disturbance in 4 neuropsychologic functions: (1) nonverbal working memory, (2) internalized self-speech, (3) self-regulation of affect-motivation-arousal, and (4) behavioral analysis and synthesis (reconstitution). Other models of ADHD have been put forth: Executive Dysfunction, State Regulation, Delay Aversion, and Dynamic Developmental (Johnson et al 2009). Working memory deficits have received increased attention as a model for inattentive ADHD (Alderson et al 2010). Impulsivity has been related to deficits in temporal processing (Rubia et al 2009). The Scandinavians maintain a broader view of the disorder and combine deficits of attention, motor control, and perception as the acronym "DAMP" (Landgren et al 1996).
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