Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by executive dysfunction occasioning symptoms of inattention, hyperactivity, impulsivity and emotional dysregulation that are excessive and pervasive, impairing in multiple contexts, and developmentally-inappropriate.[8]
ADHD symptoms arise from executive dysfunction,[17] and emotional dysregulation is often considered a core symptom.[21] Difficulties in self-regulation such as time management, inhibition and sustained attention may cause poor professional performance, relationship difficulties and numerous health risks,[22][23] collectively predisposing to a diminished quality of life[24] and a direct average reduction in life expectancy of 13 years.[25][26] ADHD is associated with other neurodevelopmental and mental disorders as well as non-psychiatric disorders, which can cause additional impairment.[7]
Although people with ADHD struggle to persist on tasks with temporally delayed consequences, they may be able to do so on tasks they find intrinsically interesting or immediately rewarding;[27][16] this is known as hyperfocus (more colloquially)[28] or perseverative responding.[29] This mental state is often hard to disengage from[30][31] and can be related to risks such as for internet addiction[32] and types of offending behaviour.[33]
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.[34][12][35][16][36][37][38][39]
The precise causes of ADHD are unknown in the majority of cases.[40][41] For most people with ADHD, many genetic and environmental risk factors accumulate to cause the disorder.[42] The environmental risks are biological and most often exert their effects in the prenatal period.[7] However, in rare cases ADHD may be caused by a single event such as traumatic brain injury,[43][44][45] exposure to biohazards during pregnancy,[7] a major genetic mutation[46] or extreme environmental deprivation very early in life.[7] There is no biologically distinct adult-onset ADHD except for when ADHD occurs after traumatic brain injury.[47][7]
Signs and symptoms
Inattention, hyperactivity (restlessness in adults), disruptive behaviour, and impulsivity are common in ADHD.[48][49][50] Academic difficulties are frequent, as are problems with relationships.[49][50][51] 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.[52]
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.[3][4] 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.[3][4] 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.[3] Additionally, several symptoms must have been present before age twelve.[4] The DSM-5 's required age of onset of symptoms is 12 years.[3][4][53] However, research indicates the age of onset should not be interpreted as a prerequisite for diagnosis given contextual exceptions.[47]
Presentations
ADHD is divided into three primary presentations:[4][52]
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.