Paediatrics: Attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder

ADHD is a complex neurodevelopmental disorder.

Prevalence

Rates of diagnosis vary greatly both between and within different coun-tries. In the US, Netherlands, and Germany, rates are much higher than in the UK, which is much higher than those in France, Italy, and Spain. A recent systematic review identified 102 studies, across all world regions. Overall prevalence of ADHD was 5.3 %. Prevalence for child-ren 6.5% and for adolescents 2.7%. ADHD is 2–3 times more common in boys. Prevalence decreases with increasing age. Differences between studies mainly accounted for by the use of differing diagnostic criteria, the source of information used to elicit symptoms and whether impairment was required to be present in order for the diagnosis to be made. After adjustments were made to account for these methodological issues, the prevalence in North America and Europe were similar.

Causes

ADHD displays considerable heterogeneity at the genetic, pathophys-iological, cognitive, and behavioural levels of analysis. Whilst the exact aetiology of ADHD is unknown considerable research supports a strong genetic component (heritability of 0.7) with non-shared environmental factors contributing most of the residual variance. Environmental fac-tors are likely to include prenatal exposure to nicotine, pre and perinatal obstetric complications and low birth weight, exposure to lead and other environmental toxins. Gene-environment interactions seem likely to be particularly important, but have not yet been studied extensively.

Diagnostic criteria

·  Inattention: e.g.

·  fails to attend to detail;

·  difficulty sustaining attention;

·  does not follow through;

·  difficulty organizing tasks, easily distracted;

·  reluctant to engage in tasks that require sustained mental effort.

·  Hyperactivity: e.g.

·  often fidgets;

·  leaves seat in classroom;

·  runs and climbs excessively;

·  often on the go;

·  acts as if driven by a motor.

·  Impulsivity: e.g.

·  often blurts out answer before the question has finished;

·  has difficulty waiting turn;

·  interrupts and butts in.

Symptoms must be present for at least 6mths, be present before age 7yrs, and result in impairment in 2 or more functional domains or settings. In DSM-IV inattentive, hyperactive–impulsive, and combined subtypes are described. The ICD-10 criteria are more restrictive and only include those

with severe, pervasive and impairing combined ADHD in the diagnostic category hyperkinetic disorder. This results in a lower prevalence for hyper-kinetic disorder of around 1.5%.

Differential diagnosis 

In young children it may be difficult to differenti-ate age-appropriate boisterousness and activity from ADHD symptoms. Inattention may be due to under-stimulation of above-average children or seen in children in classroom settings too advanced for their mental age. ADHD symptoms common in PTSD and autism spectrum disorders.

Common comorbidities

·Disruptive behaviour disorders (ODD and CDD).

·Anxiety (22–37%).

·Depression (12–17%).

·Learning, speech, and language disorders are also overrepresented.

Treatment

·Psychopharmacology: drug therapies include psychostimulants (methylphenidate, dexamfetamine) and the non-stimulant atomoxetine.

·Behavioural interventions: integrated home–school behaviour management, token economies, and parent effectiveness training. The effectiveness of family interventions is inconclusive.

A multisite randomized controlled trial (NIMH-MTS study) of combined subtype ADHD found that, over 14mths, carefully organized medication was superior to either behavioural treatment or community care (which usually included less well organized medication treatment) for core symp-toms and that a combination of behavioural and medication therapies were equally better for related symptoms compared with usual care.¹

Current UK² and European practice suggests that for those, over 6yrs of age, where ADHD is severe, pervasive, and impairing ADHD (ICD-10 hyperkinetic disorder) medication will usually be the first choice treat-ment. For those with less severe ADHD behavioural interventions are suggested as the first choice treatment with medication reserved for those who either fail to respond to the behavioural treatments or for whom behavioural treatment is not possible.

Prognosis

·70–80% continue to display symptoms and impairments as adolescents.

·50–65% as adults.

·Only 10–20% reach adulthood without any psychiatric diagnosis, functioning well, and without symptoms of their disorder.

Pharmacological treatments may be continued into adulthood