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Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by persistent patterns of inattention and/or hyperactivity-impulsivity that significantly interfere with academic, occupational, and social functioning.

Although historically considered a disorder exclusive to childhood, it is now recognized that ADHD can persist into adolescence and adulthood. Its impact goes beyond symptoms: it affects academic performance, job stability, interpersonal relationships, and mental health, and is associated with an increased risk of accidents and psychiatric comorbidities.

Pathophysiology

ADHD has a neurobiological and multifactorial basis involving neurochemical, structural, genetic, and environmental alterations:

1. Neurochemical alterations

Dopamine (DA): Hypoactivity in the prefrontal cortex and basal ganglia, limiting sustained attention and impulse control.

Norepinephrine (NA): Reduced activity in the locus coeruleus–prefrontal cortex pathway, affecting alertness, motivation, and emotional regulation.

Psychostimulants improve symptoms by increasing the synaptic availability of DA and NA.

2. Structural and functional changes

Prefrontal cortex: Smaller volume and slower maturation, affecting planning and organization.

Basal ganglia: Hypoactivity in the caudate nucleus and putamen.

Cerebellum: Alterations in the posterior vermis, related to motor control and cognitive functions.

Neuronal networks: Dysfunction in the frontostriatal network and default mode network, facilitating distractibility.

3. Delayed cortical maturation

An average delay of 2–3 years in prefrontal cortical thinning, explaining partial symptom improvement in some cases during adulthood.

4. Genetic influence

Estimated heritability is 74–80%. Associated with polymorphisms in genes such as DAT1, DRD4, SLC6A2, and ADRA2A. There is no single causal gene, but rather multiple small-effect variants.

5. Environmental and epigenetic factors

Prenatal: Maternal smoking, alcohol or drug use, infections, prematurity, low birth weight.

Postnatal: Head trauma, lead exposure, nutritional deficiencies, chaotic environments.

Epigenetic mechanisms that modulate gene expression.

Onset and Course

Age of onset: Symptoms present before age 12 (DSM-5 criterion).

Life course:

Childhood: Motor hyperactivity and attention difficulties.

Adolescence: Academic challenges, social impulsivity.

Adulthood: Disorganization, procrastination, occupational instability.

Clinical Features

Core symptoms

Inattention: Careless mistakes, difficulty sustaining attention, frequent forgetfulness.

Hyperactivity: Restlessness, excessive talking, difficulty remaining seated.

Impulsivity: Interrupting others, difficulty waiting for turns.

Clinical presentations

Predominantly inattentive

Predominantly hyperactive-impulsive

Combined type (most common)

Common comorbidities

Learning disorders

Anxiety and depressive disorders

Conduct disorder

Autism spectrum disorder

Tic disorders and Tourette syndrome

Sleep disorders

Substance abuse in adolescents and adults

Diagnosis

Diagnosis is clinical and requires:

1. Meeting DSM-5/DSM-5-TR criteria.

2. Symptoms present in two or more settings (home, school, workplace).

3. Duration of symptoms ≥6 months.

4. Interviews with the patient and family members.

5. Use of standardized scales: Vanderbilt, ADHD-RS-5 (children), ASRS (adults).

6. Exclusion of secondary causes (sleep deprivation, anxiety, depression, thyroid disorders, medication effects).

Treatment

Non-pharmacological interventions

Behavioral therapy (first-line in children under 6).

Cognitive-behavioral therapy adapted for adults.

Environmental modifications at school and workplace.

Sleep hygiene, regular physical activity, balanced nutrition.

Pharmacological treatment

Stimulants: Methylphenidate, amphetamines, lisdexamfetamine (first-line in most cases).

Non-stimulants: Atomoxetine, guanfacine XR, clonidine XR, viloxazine ER.

Choice based on age, side effect profile, comorbidities, and risk of misuse.

Side effects and monitoring

Appetite loss, insomnia, irritability.

Mild impact on height and weight (monitor growth).

Cardiovascular monitoring if risk factors present.

Atomoxetine: monitor for suicidal ideation in youth.

Risk of misuse in adolescents and adults → close follow-up.

Prognosis

With treatment: Reduced accidents, improved academic and functional performance.

Without treatment: Higher risk of school failure, unemployment, legal issues, depression, and accidents.

Prognosis improves with early diagnosis, comprehensive management, and family/school support.

Stigma and Approach

Fear of stigma can delay help-seeking and reduce adherence. Psychoeducation and the use of non-blaming language are essential to reduce prejudice and promote acceptance of the diagnosis.

Key Messages

ADHD is not a character flaw, but a neurobiological condition.

Comprehensive management combines education, therapy, and medication when indicated.

Early detection and appropriate treatment can change the long-term outlook.

Raul Ayala, MD