Attention deficit hyperactivity disorder

Overview

•Affects ~5% of children; 2-5x more common in boys (girls underdiagnosed - more often inattentive subtype)

•Heritability ~70-80% - one of the most heritable psychiatric conditions

•~50% continue to meet criteria in adulthood - inattention is the dominant persisting feature

•Pathophysiology: reduced dopaminergic and noradrenergic activity in prefrontal cortex → impaired executive function, inhibitory control, working memory

Presentation

•Inattention (≥6 symptoms in children; ≥5 in those aged ≥17): careless mistakes, difficulty sustaining attention, seems not to listen, fails to follow through, poor organisation, avoids sustained mental effort, loses things, easily distracted, forgetful

•Hyperactivity/impulsivity (≥6 in children; ≥5 in those aged ≥17): fidgets, leaves seat, runs/climbs inappropriately (adults: restlessness), talks excessively, blurts out answers, difficulty waiting turn, interrupts others

•DSM-5 additional criteria - all must be met:

•Symptoms present before age 12

•Symptoms in two or more settings (e.g. home AND school)

•Symptoms cause clinically significant impairment

•Not better explained by another mental disorder

Investigations

•ADHD is a clinical diagnosis - no blood test or scan confirms it

•Structured clinical interview - developmental, birth, educational, and family history from parents and teachers

•Standardised rating scales - e.g. Conners' Rating Scales or SDQ completed by parents and teachers

•Physical examination - height, weight, BP, HR (baseline before medication); assess for tics, dysmorphic features

•Screen for comorbidities - anxiety, depression, ASD, conduct disorder, learning disabilities

Differential Diagnosis

Key differentials

Anxiety - inattention driven by worry; situational

Depression - poor concentration with low mood/anhedonia

ASD - social communication difficulties; commonly comorbid

Conduct/ODD - defiance-driven behaviour

Bipolar disorder - episodic, not persistent

Sleep disorders - OSA causing inattention/hyperactivity

Thyroid dysfunction - TFTs if restlessness/poor concentration

Learning disabilities - cognitive testing differentiates

🎯

ADHD symptoms must be pervasive (multiple settings), persistent (not episodic), and traceable to before age 12 - these features distinguish ADHD from most differentials.

Management

•Children under 5: medication not recommended - first-line: parent-training/education programme

•Children ≥5 and adolescents:

•First-line: methylphenidate - inhibits dopamine and noradrenaline reuptake; available as immediate-release or modified-release

•Second-line: lisdexamfetamine - if methylphenidate inadequate after 6 weeks; prodrug of dexamfetamine

•Second-line (non-stimulant): atomoxetine - selective noradrenaline reuptake inhibitor; preferred if stimulants contraindicated (tic disorder, substance misuse risk, cardiac concerns); takes 4-6 weeks for full effect

•Third-line: guanfacine - alpha-2 agonist; when stimulants and atomoxetine not suitable/tolerated

•Adults (new diagnosis): refer to mental health specialist trained in adult ADHD; methylphenidate or lisdexamfetamine first-line

•Monitoring on stimulants (every review): height/weight on centile charts, BP, HR, sleep, appetite, mood, psychiatric symptoms, tics

⚠️

Stimulants are sympathomimetic - monitor BP and HR. They can also suppress appetite and growth (plot on centile charts), worsen tics, and unmask Tourette syndrome.

Complications

•Academic underachievement, school exclusion, poor self-esteem

•Conduct disorder/ODD (comorbidity in up to 50%)

•Substance misuse in adolescence/adulthood

•Road traffic accidents (impulsivity and inattention)

•Medication side effects: reduced appetite, growth suppression, insomnia, elevated BP/HR, rarely cardiac arrhythmia

Prognosis

•~50% continue to meet criteria in adulthood - ADHD is not simply grown out of

•Hyperactive-impulsive features tend to diminish with age; inattention often persists

•Early multimodal treatment improves academic attainment, employment stability, and social functioning