What is ADHD?
To be diagnosed with ADHD, a child, adolescent, or adult should meet clear diagnostic criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) or International Classification of Diseases (ICD-10). In the DSM-5 definition symptoms fall within two main areas—inattention and hyperactivity/impulsivity—and can include difficulties sustaining attention, disorganisation, lack of follow through on tasks, being easily distracted, restless, and persistently interrupting. This results in three subtypes (predominantly inattentive, predominantly hyperactive/impulsive, and combined). The ICD-10 calls the condition hyperkinetic disorder and requires hyperactivity, impulsivity, and inattention to be present. The more restrictive diagnostic criteria of ICD-10 result in smaller prevalence rates than ADHD diagnosed using DSM criteria.4 However, most practitioners use DSM.
ADHD is diagnosed more often in boys than girls (about 3:1) and usually within the primary school years.9 However, girls are more likely to meet criteria for the inattentive subtype of ADHD.10 Although this subtype was dropped from DSM-III-R, it was reintroduced in DSM-IV, corresponding to a substantial increase in diagnoses among girls.11
ADHD is usually diagnosed by paediatricians and psychiatrists after a child in whom the diagnosis is suspected has been referred by their primary care physician.5 12 13 In the US, however, primary care paediatricians predominantly provide diagnoses.6 Diagnosis depends on an evaluation of the child’s behaviour in at least two contexts (usually home and school or workplace) and different people (often parents and teachers) completing the evaluations. Symptoms must impair functioning in social, academic, or work settings.8 Although there are some assessment scales that attempt to quantify impairment (such as the Children’s Global Assessment Scale), the DSM-5 and national ADHD guidelines leave it to individual clinicians to decide impairment severity.5 6 7 Guidelines suggest that medical, psychosocial, and developmental assessments are also carried out.5 6 7
Children who meet DSM’s ADHD criteria always have problems in academic achievement14 and social interaction. Often children also experience peer rejection and an increased risk of injury.15 16 Longitudinal studies show that they are less likely to attend tertiary education, more likely to be unemployed or perform suboptimally at work,17 more likely to engage in delinquent or criminal behaviour,18 and more likely to use alcohol, tobacco, and illegal drugs than those without ADHD.19 Observational studies suggest that untreated adults with ADHD are more likely to have car crashes and traffic violations than treated adults and adults without ADHD.20
Rising diagnosis and treatment
The reported prevalence of ADHD is rising in several countries.21 In US population surveys the prevalence of parent reported diagnosis of ADHD rose from 6.9% in 1997 to 9.5% in 2007,3 and there is wide variation in point prevalence rates within22 and between countries,21 raising questions about diagnostic practices contributing to part of the rise. It is likely that clinicians are better at detecting and diagnosing ADHD but it is also thought that some of the rise reflects overdiagnosis or misdiagnosis.23 24
In parallel, prescribing rates for commonly used drugs such as dexamfetamine, methylphenidate, and atomoxetine for children diagnosed with ADHD have increased. Australian data on prescribing rates for ADHD medication show an increase of 72.9% between 2000 and 2011.25 In the UK prescription of these same medications increased twofold for children and adolescents between 2003 and 2008 and fourfold for adults.26 Prescribing of methylphenidates and amfetamines in the US increased steadily between 1996 and 2008, with the greatest increase in adolescents aged 13-18 years.27 In the Netherlands prevalence and prescribing rates for children who had ADHD diagnosed doubled between 2003 and 2007.28
How effective is treatment?
Systematic reviews reach differing conclusions about the benefits of treatment in the short term,29 30 and few studies have examined long term benefits.31 Parent training programmes are effective for preschool children and their families.30 Among children aged 6 years and older drug treatment with or without parent training was effective, but parent training alone had no benefit.29 31 The longest trial of ADHD treatment outcomes available is the Multimodal Treatment Study of Children with ADHD. Although not without methodological controversies, the study reported short term benefits for medication alone and combination treatments compared with behaviour treatment alone or community care. At three, six, and eight year follow-up, children were, on average, performing better than at baseline, although they were still underperforming compared with their peers and there were no differences in treatment groups.32
Drivers of overdiagnosis
Shifting definitions
An important contributor to the increasing prevalence of ADHD is changes to the diagnostic criteria in differing editions of the DSM (table⇓).21 33The figure⇓shows individual and average pooled prevalence from 104 studies that used DSM criteria. These show a significant increase in ADHD prevalence between each version of DSM. Field trials of proposed changes to ADHD diagnostic criteria (from DSM III-R to DSM-IV) flagged an expected increase in prevalence of 15%.33 However, the increase exceeded this prediction, and prevalence is expected to rise further with the adoption of DSM-5, launched earlier this year.
