Attention Deficit Hyperactivity Disorder

A neurodevelopmental disorder characterised by a persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development, present across multiple settings (home, school, and social contexts) and with onset in childhood.

It is one of the commonest neurodevelopmental conditions of childhood, persisting into adolescence and, in a substantial proportion of affected individuals, adulthood.

The diagnosis is established through full, structured clinical assessment rather than any single, definitive diagnostic test.

A combination of behavioural intervention and, where indicated, pharmacological treatment represents the established, evidence-based management approach.

Classification and pathophysiology

• The condition is classified into three presentations according to the predominant symptom pattern:
  • Predominantly inattentive presentation: difficulty sustaining attention, organisational difficulty, and a tendency toward distractibility and forgetfulness, without prominent hyperactivity or impulsivity. It is frequently under-recognised, particularly in girls, because it is less overtly disruptive and externally apparent than the hyperactive-impulsive pattern.
  • Predominantly hyperactive-impulsive presentation: excessive motor activity, difficulty remaining seated, and impulsive behaviour, without prominent inattention.
  • Combined presentation: criteria met for both symptom domains. It is the commonest presentation overall, particularly in younger children.
• The underlying pathophysiology reflects a complex interplay of genetic and environmental factors.
• Genetic predisposition is central: the condition shows among the highest heritability of the common neurodevelopmental and psychiatric conditions.
• In a smaller proportion of cases, environmental factors contribute, including prenatal exposure to alcohol, tobacco, or certain other substances, and significant prematurity.
• Neuroimaging shows subtle, though consistent, differences in the structure and function of brain regions and networks involved in executive function, attention, and reward processing, particularly relating to dopaminergic and noradrenergic neurotransmitter systems. This provides the pharmacological basis for the effect of stimulant medication.
• Attention deficit hyperactivity disorder frequently coexists with other neurodevelopmental and psychiatric conditions: autism spectrum disorder, specific learning disorders, anxiety disorders and, particularly in adolescence and adulthood, mood disorders and substance use disorders.
• Careful assessment for these coexisting conditions is an integral component of evaluation.

• Inattentive symptoms include:
  • difficulty sustaining attention in tasks or play
  • appearing not to listen when spoken to directly
  • failure to follow through on instructions and difficulty finishing tasks
  • difficulty organising tasks and activities
  • avoidance of tasks requiring sustained mental effort
  • losing items necessary for tasks
  • distractibility by extraneous stimuli
  • forgetfulness in daily activities
• Hyperactive-impulsive symptoms include:
  • fidgeting or squirming
  • difficulty remaining seated when expected to do so
  • excessive running or climbing in inappropriate situations
  • difficulty engaging in activities quietly
  • appearing to be "driven by a motor"
  • excessive talking
  • blurting out answers before a question has been completed
  • difficulty waiting their turn
  • interrupting or intruding on others
• Diagnostic criteria require:
  • a sufficient number of these symptoms: generally at least six from the relevant symptom domain in children, or five in adolescents and adults, reflecting some symptom attenuation with age
  • persistence for a minimum of six months
  • onset before the age of twelve years, even where formal diagnosis occurs later
  • symptoms evident across multiple settings
  • clear evidence of functional impairment
• The requirement for cross-situational impairment and functional impact is the essential element distinguishing genuine attention deficit hyperactivity disorder from developmentally typical variation in attention and activity level.
• Presentation and symptom expression frequently evolve with age.
• Overt hyperactivity often becomes less prominent in adolescence and adulthood, sometimes manifesting instead as a subjective sense of inner restlessness.
• Inattentive symptoms and their functional impact, particularly on organisation, time management, and sustained task completion, frequently persist. They can become increasingly significant as academic, occupational, and life demands for these executive function skills increase.
• Functional impairment spans academic, social, and family domains:
  • difficulty with peer relationships, reflecting impulsivity and difficulty with social reciprocity
  • academic underachievement relative to underlying ability
  • increased risk of accidental injury, reflecting impulsivity
  • in adolescence and adulthood, an increased risk of substance use, motor vehicle accidents, and relationship and occupational difficulty if the condition remains unrecognised or inadequately managed
• This underscores the cumulative impact of the condition when inadequately identified and supported.

• Diagnosis is established through full clinical assessment, incorporating a detailed developmental and behavioural history from parents or carers, together with information from school or other relevant settings.
• Symptoms and impairment must be evident across multiple settings, rather than confined to a single context.
• Structured, validated rating scales completed by parents and teachers support systematic, standardised assessment of the relevant symptom domains.
• Full assessment for coexisting conditions, including screening for autism spectrum disorder, specific learning difficulty, and relevant mood or anxiety symptoms, forms an important, integral component of full evaluation, given the frequent coexistence of these conditions and the direct relevance to full, appropriately targeted management planning.
• No specific laboratory or neuroimaging test can confirm or exclude the diagnosis; assessment rests entirely on full clinical and behavioural evaluation.
• Baseline physical assessment, including height, weight, and cardiovascular assessment, is a standard component of pre-treatment evaluation. It is directly relevant to monitoring stimulant medication where this is initiated.
• Careful, systematic exclusion of alternative explanations for the presenting symptoms is an essential component of accurate diagnostic assessment.
• Alternatives include hearing or visual impairment, sleep disorders, and adverse psychosocial circumstances, each of which can produce symptoms with some overlapping features.
• Consider also the child's overall developmental level and the appropriateness of expected behaviour for their specific age.

• Behavioural intervention is a foundational component of management across the full range of severity.
• It includes structured parent training programmes, teaching behavioural management strategies including consistent routine, clear expectations, and positive reinforcement, and, where relevant, classroom-based behavioural strategies and accommodations.
• It is generally the recommended first line approach for preschool-aged children, given the more limited evidence base and specific safety considerations of pharmacological treatment in this youngest age group.
• Stimulant medication (methylphenidate or amphetamine-based preparations) is the most extensively evidenced and generally most effective pharmacological treatment for attention deficit hyperactivity disorder in school-age children, adolescents, and adults.
• A range of formulations with differing durations of action allows treatment to be tailored to the individual's daily schedule and needs.
• Treatment response is generally assessed and titrated over a structured initial period.
• Non-stimulant medications are alternative pharmacological options: atomoxetine (a selective noradrenaline reuptake inhibitor) and guanfacine or clonidine (alpha-2 adrenergic agonists).
• They are particularly relevant where:
  • stimulant medication is contraindicated or not tolerated
  • there is significant misuse concern within the family or individual
  • a coexisting condition, including significant anxiety or tic disorder, makes a non-stimulant approach preferable
• Effect size is generally somewhat more modest than with stimulant medication for the core attention deficit hyperactivity disorder symptoms.
• Regular, structured monitoring of treatment response and adverse effects is essential for any child or adult commenced on pharmacological treatment:
  • growth (height and weight), given a recognised, generally modest effect of stimulant medication on growth trajectory, which bears on the ongoing discussion of the balance of benefits and this consideration
  • cardiovascular parameters (heart rate and blood pressure)
  • appetite and sleep
• Reassess ongoing symptom control and functional benefit regularly.
• Educational support and accommodation is an integral component of management, given the substantial relevance of the educational environment and its accommodations to overall functional outcome.
• It includes, where relevant and available, formal educational support plans addressing specific identified needs, together with support for any coexisting specific learning difficulty.
• Ongoing psychosocial support for the affected individual and their family underpins individualised, evidence-based long-term management of this common neurodevelopmental condition. It addresses the practical and emotional impact of the condition on family functioning.
• Structured transition planning is needed as the individual moves from childhood through adolescence into adulthood.
• In a substantial proportion of affected individuals the condition and its functional impact persist into adult life, warranting continued access to appropriate adult services and ongoing management where relevant.