Attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD)[1] is a neurodevelopmental disorder characterised by symptoms of inattention, hyperactivity, impulsivity, and emotional dysregulation that are excessive and pervasive, impairing in multiple contexts, and developmentally inappropriate.[9] ADHD symptoms arise from executive dysfunction.[18]

Impairments resulting from deficits in self-regulation such as time management, inhibition, task initiation, and sustained attention[19] can include poor professional performance, relationship difficulties, and numerous health risks,[20][21] collectively predisposing to a diminished quality of life[22] and a reduction in life expectancy.[23][24] As a consequence, the disorder costs society hundreds of billions of US dollars each year, worldwide.[25] It is associated with other mental disorders as well as non-psychiatric disorders, which can cause additional impairment.[8]

While ADHD involves a lack of sustained attention to tasks,[17][20] inhibitory deficits also can lead to difficulty interrupting an already ongoing response pattern, manifesting in the perseveration of actions despite a change in context whereby the individual intends the termination of those actions.[26][27] This symptom is known colloquially as hyperfocus[28] and is related to risks such as addiction[29][30] and types of offending behaviour.[31] ADHD can be difficult to tell apart from other conditions.[16][22] ADHD represents the extreme lower end of the continuous dimensional trait (bell curve) of executive functioning and self-regulation, which is supported by twin, brain imaging and molecular genetic studies.[38]

The precise causes of ADHD are unknown in most individual cases.[39][40] Meta-analyses have shown that the disorder is primarily genetic with a heritability rate of 70–80%,[41][42][43] where risk factors are highly accumulative.[44] The environmental risks are not related to social or familial factors;[45][46][47] they exert their effects very early in life, in the prenatal or early postnatal period.[8] However, in rare cases, ADHD can be caused by a single event including traumatic brain injury,[41][48][49][50] exposure to biohazards during pregnancy,[8] or a major genetic mutation.[51] As it is a neurodevelopmental disorder, there is no biologically distinct adult-onset ADHD except for when ADHD occurs after traumatic brain injury.[8][52]

Signs and symptoms

Inattention, hyperactivity (restlessness in adults), disruptive behaviour, and impulsivity are common in ADHD.[53][54][55] Academic difficulties are frequent, as are problems with relationships.[54][55][56] The signs and symptoms can be difficult to define, as it is hard to draw a line at where normal levels of inattention, hyperactivity, and impulsivity end and significant levels requiring interventions begin.[57]

According to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and its text revision (DSM-5-TR), symptoms must be present for six months or more to a degree that is much greater than others of the same age.[4][5] This requires at least six symptoms of either inattention or hyperactivity/impulsivity for those under 17 and at least five symptoms for those 17 years or older.[4][5] The symptoms must be present in at least two settings (e.g., social, school, work, or home), and must directly interfere with or reduce quality of functioning.[4] Additionally, several symptoms must have been present before age 12 as per DSM-5 criteria.[5][4][58] However, research indicates the age of onset should not be interpreted as a prerequisite for diagnosis given contextual exceptions.[52]

Presentations

ADHD is divided into three primary presentations:[5][57]

predominantly inattentive (ADHD-PI or ADHD-I)

predominantly hyperactive-impulsive (ADHD-PH or ADHD-HI)

combined presentation (ADHD-C).

The table "Symptoms" lists the symptoms for ADHD-I and ADHD-HI from two major classification systems. Symptoms which can be better explained by another psychiatric or medical condition which an individual has are not considered to be a symptom of ADHD for that person. In DSM-5, subtypes were discarded and reclassified as presentations of the disorder that change over time.