Attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder 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. ADHD symptoms arise from executive dysfunction.
Impairments resulting from deficits in self-regulation such as time management, cognitive inhibition, task initiation, and sustained attention can include poor professional performance, relationship difficulties, and numerous health risks, collectively predisposing to a diminished quality of life and a reduction in life expectancy. It is associated with other mental disorders as well as non-psychiatric disorders, which can cause additional impairment.
While ADHD involves a lack of sustained attention to tasks, 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. This symptom is known colloquially as hyperfocus and is related to risks such as addiction and types of offending behaviour. ADHD can be difficult to tell apart from other conditions. ADHD represents the extreme lower end of the continuous dimensional trait of executive functioning and self-regulation, which is supported by twin, brain imaging and molecular genetic studies.
The precise causes of ADHD are unknown in most individual cases. Meta-analyses have shown that the disorder is primarily genetic with a heritability rate of 70–80%, where risk factors are highly accumulative. The environmental risks are not related to social or familial factors; they exert their effects very early in life, in the prenatal or early postnatal period. However, in rare cases, ADHD can be caused by a single event including traumatic brain injury, exposure to biohazards during pregnancy, or a major genetic mutation. As it is a neurodevelopmental disorder, there is no biologically distinct adult-onset ADHD except for when ADHD occurs after traumatic brain injury.

Signs and symptoms

Inattention, hyperactivity, disruptive behaviour, and impulsivity are common in ADHD. Academic difficulties are frequent, as are problems with relationships. A diagnosis can be hard to ascertain, as it is hard to distinguish between normal levels of symptoms and levels that cause significant impairment in major life activities.
According to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders and its text revision, symptoms must be present for six months or more to a degree that is much greater than others of the same age. 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. The symptoms must be present in at least two settings, and must directly interfere with or reduce quality of functioning. Additionally, several symptoms must have been present before age 12 as per DSM-5 criteria. However, research indicates the age of onset should not be interpreted as a prerequisite for diagnosis given contextual exceptions.

Presentations

ADHD is divided into three primary presentations:

predominantly inattentive
predominantly hyperactive-impulsive
combined presentation.

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.

Presentations	and symptoms	symptoms
Inattention	Six or more of the following symptoms in children, and five or more in adults, excluding situations where these symptoms are better explained by another psychiatric or medical condition: Frequently overlooks details or makes careless mistakes Often has difficulty maintaining focus on one task or play activity Often appears not to be listening when spoken to, including when there is no obvious distraction Frequently does not finish following instructions, failing to complete tasks Often struggles to organise tasks and activities, to meet deadlines, and to keep belongings in order Is frequently reluctant to engage in tasks which require sustained attention Frequently loses items required for tasks and activities Is frequently easily distracted by extraneous stimuli, including thoughts in adults and older teenagers Often forgets daily activities, or is forgetful while completing them.	Multiple symptoms of inattention that directly negatively impact occupational, academic or social functioning. Symptoms may not be present when engaged in highly stimulating tasks with frequent rewards. Symptoms are generally from the following clusters: Struggles to maintain focus on tasks that are not highly stimulating/rewarding or that require continuous effort; details are often missed, and careless mistakes are frequent in school and work tasks; tasks are often abruptly abandoned in favour of another before they are completed. Easily distracted ; may not listen when spoken to; frequently appears to be lost in thought Often loses things; is forgetful and disorganised in daily activities. The individual may also meet the criteria for hyperactivity-impulsivity, but the inattentive symptoms are predominant.
Hyperactivity-Impulsivity	Six or more of the following symptoms in children, and five or more in adults, excluding situations where these symptoms are better explained by another psychiatric or medical condition: Is often fidgeting or squirming in seat Frequently has trouble sitting still during dinner, class, in meetings, etc. Frequently runs around or climbs in inappropriate situations. In adults and teenagers, this may be present only as restlessness. Often cannot quietly engage in leisure activities or play Frequently seems to be "on the go" or appears uncomfortable when not in motion Often talks excessively Often answers a question before it is finished, or finishes people's sentences Often struggles to wait their turn, including waiting in lines Frequently interrupts or intrudes, including into others' conversations or activities, or by using people's things without asking.	Multiple symptoms of hyperactivity/impulsivity that directly negatively impact occupational, academic or social functioning. Typically, these tend to be most apparent in environments with structure or which require self-control. Symptoms are generally from the following clusters: Excessive motor activity; struggles to sit still, often leaving their seat; prefers to run about; in younger children, will fidget when attempting to sit still; in adolescents and adults, a sense of physical restlessness or discomfort with being quiet and still. Talks too much; struggles to quietly engage in activities. Blurts out answers or comments; struggles to wait their turn in conversation, games, or activities; will interrupt or intrude on conversations or games. A lack of forethought or consideration of consequences when making decisions or taking action, instead tending to act immediately. The individual may also meet the criteria for inattention, but the hyperactive-impulsive symptoms are predominant.
Combined	Meet the criteria for both inattentive and hyperactive-impulsive ADHD.	Criteria are met for both inattentive and hyperactive-impulsive ADHD, with neither clearly predominating.

Girls and women with ADHD tend to display fewer hyperactivity and impulsivity symptoms but more symptoms of inattention and distractibility.
Symptoms are expressed differently and more subtly as the individual ages. Hyperactivity tends to become less overt with age and turns into inner restlessness, difficulty relaxing or remaining still, talkativeness or constant mental activity in teens and adults with ADHD. Impulsivity in adulthood may appear as thoughtless behaviour, impatience, irresponsible spending and sensation-seeking behaviours, while inattention may appear as becoming easily bored, difficulty with organisation, remaining on task and making decisions, and sensitivity to stress.

Characteristics in childhood

Difficulties managing anger are more common in children with ADHD, as are delays in speech, language and motor development. Poorer handwriting is more common in children with ADHD. Poor handwriting can be a symptom of ADHD in itself due to decreased attentiveness. When this is a pervasive problem, it may also be attributable to dyslexia or dysgraphia. There is significant overlap in the symptomatologies of ADHD, dyslexia, and dysgraphia, and 3 in 10 people diagnosed with dyslexia experience co-occurring ADHD. Although it causes significant difficulty, many children with ADHD have an attention span equal to or greater than that of other children for tasks and subjects they find interesting.

Emotional dysregulation

Although not listed as an official symptom, emotional dysregulation or mood lability is generally understood to be a common symptom of ADHD.

Relationship difficulties

People with ADHD of all ages are more likely to have problems with social skills, such as social interaction and forming and maintaining friendships. This is true for all presentations. About half of children and adolescents with ADHD experience social rejection by their peers compared to 10–15% of non-ADHD children and adolescents. People with attention deficits are prone to having difficulty processing verbal and nonverbal language which can negatively affect social interaction. They may also drift off during conversations, miss social cues, and have trouble learning social skills.