Attention-Deficit/Hyperactivity Disorder in Adults

DEFINITION AND ETIOLOGY

Attention-deficit/hyperactivity disorder (ADHD) is the current diagnosis for what was previously labeled minimal brain damage, minimal brain dysfunction, hyperkinetic impulse disorder, and hyperactive child syndrome.¹ Contrary to popular belief, at least 60% of children with ADHD continue to exhibit features of the disorder during adulthood. ADHD in adults is associated with significant psychiatric morbidity and higher than average rates of divorce, unemployment, substance abuse, and motor vehicle accidents.² Poor adjustment and performance can have an erosive effect on self-esteem, leading to clinically significant anxiety or depression, or both, which are often the presenting features of adult ADHD in the primary care setting.

PREVALENCE AND RISK FACTORS

ADHD is a neurobiologic disorder with strong genetic determinants. Strict application of diagnostic criteria has been associated with a mean prevalence of 5% to 7% across studies of children and adolescents.³ Approximately 60% to 70% of affected children transition into adulthood with some or all of the signs and symptoms of the disorder.³

Family and genetic studies have shown ADHD to be the most heritable of psychiatric disorders.⁴ Results from the National Comorbidity Survey Replication estimated a 4.4% prevalence of current ADHD in the U.S. adult population.⁵ There was a high rate of psychiatric comorbidity in ADHD adults: 38% had a mood disorder, 47% had an anxiety disorder, 15% had a substance-use disorder, and nearly 20% had an impulse-control disorder. The odds of having both ADHD and another disorder were highest for drug dependence (odds ratio [OR], 7.9), dysthymia (OR, 7.5), and bipolar disorder (OR, 7.4).⁵

PATHOPHYSIOLOGY AND NATURAL HISTORY

A variety of neurochemical and neuroanatomic deficits have been associated with ADHD.^1,^6,⁷ Studies employing structural neuroimaging point to an absence, in persons with ADHD, of the frontal lobe asymmetry seen in normal controls¹; in control subjects (no ADHD), the right frontal lobe tends to be larger than the left. Structural and functional neuroimaging studies have demonstrated decreased function and size of the prefrontal cortex, anterior cingulate, caudate nucleus, and cerebellar vermis in ADHD children, and most (but not all) studies demonstrate this deficit on the right.⁶^–⁸

Candidate gene selection is based on the hypothesis that deficient dopamine availability contributes to ADHD. Genes studied include those relevant to production of proteins involved in dopamine synthesis (dopa decarboxylase, the enzyme responsible for conversion of L-dopa to dopamine), inactivation (the dopamine and norepinephrine transporters), and degradation (catechol-O-methyltransferase) and in dopamine receptor activity (especially the dopamine D₄ receptor).⁷ No one gene or its protein derivatives has been found to have a consistent relation with ADHD, which suggests that like most psychiatric disorders, ADHD is the consequence of polygenetic influences.

SIGNS AND SYMPTOMS

The manifestations of ADHD in adults are generally less obvious than in children. Adults tend not to exhibit the impulsive, overactive behavior distinctive of many ADHD children and adolescents.^1,² Common dysfunctional behavioral patterns in adults with ADHD include task avoidance, waiting until the last moment to complete a task, completing all but the most important tasks, and taking on new tasks before finishing others (Table 1).² Impatience, irritability, and explosiveness are common as well. Common comorbidities complicate the array of signs and symptoms that ADHD adults can present with. Abnormal mood, vocational and interpersonal problems, and substance abuse are often the problems that patients present with when the underlying primary diagnosis is ADHD.

Table 1 Common Dysfunctional Behavior Patterns in Adults with ADHD

Behavior	Description	Short-Term Gain and Long-Term Loss
Anticipatory avoidance	Magnifying the difficulty of a pending task and doubts about being able to complete it	Defers short-term stress but often creates a self-fulfilling prophecy because the task looms ahead and can seem overwhelming when facing a deadline
Anticipatory avoidance	Results in rationalizations to justify procrastination
Brinkmanship	Waiting until the last moment (e.g., the night before) to complete a task, often when facing an impending deadline	Deadline-associated stress can be focusing, but this tactic leaves little room for error and can yield a substantial result
Pseudoefficiency	Completing several low-priority, manageable tasks (e.g., checking e-mail) but avoiding high-priority tasks (e.g., a project for work)	Creates sense of productivity by reducing items on a to-do list but defers a more difficult project
Juggling	Taking on new, exciting projects and feeling busy without completing projects already started	It is easier to become motivated to start a novel project than to complete an ongoing one
Juggling		Pattern usually results in several incomplete projects

ADHD, attention-deficit/hyperactivity disorder.

Adapted with permission from Rostain AL, Ramsay JL: Adults with ADHD? Try medication and psychotherapy. Curr Psychiatry 2006;5:13-27.

DIAGNOSIS

Diagnostic criteria have been developed for children and adolescents (Box 1)⁹ but not specifically for adults. Despite having clinically significant ADHD, many adults do not fulfill the threshold of six or more criteria defined for children and adolescents. This points to the fundamental problem of employing a descriptive nosology to define clinical disorders. Future editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM) will struggle with this dilemma until the pathophysiologic mechanisms of specific psychiatric disorders such as ADHD are better understood.

Box 1 Diagnostic Criteria for Attention-Deficit/Hyperactivity Disorder

Adapted from American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, 4th ed, text rev. Washington, DC: American Psychiatric Association, 2000.