The essential feature of attention-deficit/hyperactivity disorder (ADHD) is a persistent pattern of inattention and / or hyperactivity-impulsivity that interferes with functioning or development. Inattention manifests behaviorally in ADHD as wandering off task, lacking persistence, having difficulty sustaining focus, and being disorganized and is not due to defiance or lack of comprehension. Hyperactivity refers to excessive motor activity (such as a child running about) when it is not appropriate, or excessive fidgeting, tapping, or talk- ativeness. In adults, hyperactivity may manifest as extreme restlessness or wearing others out with their activity. Impulsivity refers to hasty actions that occur in the moment without forethought and that have high potential for harm to the individual (e.g., darting into the street without looking). Impulsivity may reﬂect a desire for immediate rewards or an in- ability to delay gratification. Impulsive behaviors may manifest as social intrusiveness (e.g., interrupting others excessively) and / or as making important decisions without con- sideration of long—term consequences (e.g., taking a job without adequate information).
ADHD begins in childhood. The requirement that several symptoms be present before age 12 years conveys the importance of a substantial clinical presentation during child- hood. At the same time, an earlier age at onset is not specified because of difficulties in es- tablishing precise childhood onset retrospectively. Adult recall of childhood symptoms tends to be unreliable, and it is beneficial to obtain ancillary information.
Manifestations of the disorder must be present in more than one setting (e.g., home and school, work). Confirmation of substantial symptoms across settings typically cannot be done accurately without consulting informants who have seen the individual in those set- tings. Typically, symptoms vary depending on context within a given setting. Signs of the disorder may be minimal or absent when the individual is receiving frequent rewards for appropriate behavior, is under close supervision, is in a novel setting, is engaged in espe- cially interesting activities, has consistent external stimulation (e.g., via electronic screens), or is interacting in one-on-one situations (e.g., the clinician‘s office).
Mild delays in language, motor, or social development are not specific to ADHD but often co- occur. Associated features may include low frustration tolerance, irritability, or mood lability.
Even in the absence of a specific learning disorder, academic or work performance is often im- paired. Inattentive behavior is associated with various underlying cognitive processes, and in- dividuals with ADHD may exhibit cognitive problems on tests of attention, executive function, or memory, although these tests are not sufficiently sensitive or specific to serve as di- agnostic indices. By early adulthood, ADHD is associated with an increased risk of suicide at- tempt, primarily when comorbid with mood, conduct, or substance use disorders.
No biological marker is diagnostic for ADHD. As a group, compared with peers, chil— dren with ADHD display increased slow wave electroencephalograms, reduced total brain volume on magnetic resonance imaging, and possibly a delay in posterior to anterior cortical maturation, but these findings are not diagnostic. In the uncommon cases where there is a known genetic cause (e.g., Fragile X syndrome, 22q11 deletion syndrome), the
ADHD presentation should still be diagnosed.
Population surveys suggest that ADHD occurs in most cultures in about 5% of children and about 2.5% of adults.
Many parents first observe excessive motor activity when the child is a toddler, but symp- toms are difficult to distinguish from highly variable normative behaviors before age 4 years. ADHD is most often identified during elementary school years, and inattention be- comes more prominent and impairing. The disorder is relatively stable through early ad- olescence, but some individuals have a worsened course with development of antisocial behaviors. In most individuals with ADHD, symptoms of motoric hyperactivity become less obvious in adolescence and adulthood, but difficulties with restlessness, inattention, poor planning, and impulsivity persist. A substantial proportion of children with ADHD remain relatively impaired into adulthood.