Introduction
Attention Deficit Hyperactivity Disorder_Disease Background
Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder defined by impairing levels of inattention, disorganization, and/or hyperactivity-impulsivity. Inattention and disorganization are the inability to stay on task, lack of listening skills, and losing materials necessary for tasks, at levels that are inconsistent with age or developmental level. Hyperactivity-impulsivity involves overactivity, fidgeting, inability to stay seated, intruding into other people’s activities, and inability to wait, and symptoms that are excessive for age or developmental level. Attention-deficit/hyperactivity disorder frequently overlaps with externalizing disorders (eg oppositional defiant disorder, conduct disorder) during childhood and often persists into adulthood, with resultant impairments of social, academic, and occupational functioning.
Epidemiology
Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent psychiatric disorder worldwide, particularly affecting children and adolescents. An estimated 47 million children and young people under 20 worldwide had ADHD in 2021, representing an overall prevalence of 1.78%. ADHD affects approximately 5 –9% of school-aged children, with a higher prevalence among males.
Australia had the highest ADHD burden among individuals under 20, while Western Europe and East Asia showed the largest increases in prevalence and incidence rates. South Asia had the greatest decline in incidence. Diagnosis rates are highest among White children, followed by Black and Hispanic children, with the lowest rates among Asian children.
Pathophysiology
Attention-deficit/hyperactivity disorder (ADHD) is multifactorial, involving genetic, neural, and environmental factors. ADHD is associated with dopamine and norepinephrine dysregulation, possible low serotonin activity, and structural and functional abnormalities in brain regions (eg frontal lobes, inferior parietal cortex, basal ganglia, corpus callosum, and cerebellum) involved in attention and behavior. These changes may cause delayed cortical maturation and difficulties with attention, cognitive processing, motor planning, and processing speed.
Risk Factors
ADHD risk is associated with genetic, prenatal (eg maternal health, stress, smoking, and alcohol use during pregnancy), perinatal (eg prematurity, low birth weight, and birth complications), nutritional, and environmental factors (eg secondhand smoke, excessive screen time, and neurotoxin [eg lead, mercury] exposure). Risk is also higher in children with certain neurologic or genetic disorders (eg epilepsy, neurofibromatosis) and those with a family history of ADHD or other psychiatric disorders (eg mood, anxiety disorders), learning disabilities, or autoimmune diseases.