Attention deficit hyperactivity disorder: characteristics and diagnosis

Introduction

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterised by age-inappropriate levels of inattention, hyperactivity and impulsivity​[1,2]​. These symptoms lead to an impairment in functioning across multiple settings — such as home, education, employment and the wider community — and have the potential to influence the developmental trajectory of the individual​[2]​.

The prevalence of ADHD varies significantly worldwide owing to the variable diagnostic practices and how rigorously the criterion for impairment is applied​[2]​. If the ‘Diagnostic and Statistical Manual of Mental Health Disorders’ (DSM) IV classification are applied, the prevalence can range from between 6.8% to 15.8%. The British Child and Mental Health Survey reported a prevalence of 3.6% in male children and less than 1% in female children. The ratio of boys to girls with ADHD is 4:1; however, in adults this is closer to 1:1 and is distributed across all social classes​[2]​.

Up to 87% of children diagnosed with ADHD will have one or more comorbidities, while 67% will have at least two​[1]​. These can include autism spectrum disorder (ASD), oppositional defiance disorder (ODD), major depression and generalised anxiety disorder (GAD)​[1]​. Up to 85% of children continue to experience symptoms into adolescence and up to 60% will continue to do so into adulthood​[1]​.

This article is the first in a two-part series and focuses on the diagnosis of ADHD. Information relating to management and support can be found in ‘Attention deficit hyperactivity disorder: management and support‘.

Recognition and identification

The core symptoms of ADHD are inattention, hyperactivity and impulsivity (see Figure 1). These symptoms and the related functional impairments emerge in childhood, usually before the age of 12 years and change across the lifespan​[2,3]​. Inattention symptoms are more noticeable in adolescence and usually persist through to adulthood​[3,4]​. Inattention is characterised by a disorganised style and difficulty sustaining focus to complete tasks​[2]​. Hyperactivity symptoms typically manifest as excessive motor activity. In pre-school children this may present as constant and demanding extremes of activity; in school-aged children it may involve excess movements in situations that require behavioural self-control​[2]​. In adolescents and adults, these symptoms are less overt and may manifest as excessive fidgeting or an inner sense of restlessness​[2,3]​. Impulsivity symptoms usually persist throughout life and resemble impatience or taking hasty actions without considering the consequences, culminating in high risk behaviours​[2,5]​.

The aetiology of ADHD is complex and not fully understood. It is thought to involve multiple genetic and environmental factors, which lead to altered brain neurochemistry and structure​[2,7]​ (see Box 1). Mean heritability is estimated at 77% based on twin studies​[2,8]​.

Other risk factors associated with ADHD include: low birth weight; maternal smoking or alcohol consumption and exposure to toxins (e.g. lead) during pregnancy; psychosocial adversity (e.g. bereavement, abuse, poverty); and adverse maternal mental health​[2,7]​.

Primary care practitioners play an important role in the early identification and referral of individuals with suspected ADHD​[2]​. Concerns may originate from parents, teachers or other caregivers​[5]​. When a child or young person presents with symptoms suggestive of ADHD, practitioners should determine the severity of the problems, how these affect the young person and the family and the extent to which they pervade different domains, (such as the home, school, place of work and local community)​[9]​.

If symptoms are causing an adverse impact on a child or young person’s development or family life, recommendations are to​[9]​:

• Consider a period of watchful waiting (up to 10 weeks);
• Offer parents or carers a referral to group-based ADHD-focused support (this should be offered immediately and should not wait until after a formal diagnosis).

Persistent problems causing significant impairment lead to a referral to secondary care. Referrals can be made by primary care professionals, education providers, social care, or youth justice professionals. The referrer should inform the individual’s GP. Note that care pathways may vary locally​[9]​.

Adults presenting with ADHD symptoms in primary care or general adult psychiatric services who do not have a childhood diagnosis should be referred for a specialist assessment. The criteria should include evidence that symptoms​[9]​: 

• Began during childhood and have persisted throughout life;
• Are not explained by other psychiatric diagnoses.

Adults previously treated for ADHD as children or young people who continue to have symptoms should be referred to general psychiatric services for assessment. In all cases, the symptoms should be associated with significant functional impairment​[9]​.

Diagnosis

Diagnosing ADHD is a process undertaken by psychiatrists, paediatricians and other trained healthcare professionals who have specialist expertise in its diagnosis and management​[9]​. It involves careful and comprehensive collation of information about an individual from multiple sources, including parents/carers and children, school teachers, the behaviours observed in each setting, structured observations and a full developmental and psychiatric history​[9]​. 

Screening tools — such as the ‘Strengths and Difficulties Questionnaire’ (SDQs), Swanson Nolan and Pelham questionnaire (SNAP-IV), and Conner’s questionnaire — are used to supplement the information collated to aid diagnosis but do not replace the process described above​[9]​. Screening tools are also helpful in monitoring the response to treatment and changes in symptoms​[2]​.

This information is then interpreted against the DSM-5 or ICD-11 criteria for ADHD (see Box 2)​[9,10]​.

Evidence suggests that ADHD in females is underrecognised and underdiagnosed because female children are less likely to exhibit impulsive, hyperactive and disruptive behaviours prompting evaluation and referral​[1]​. Female children predominantly display symptoms of inattention and may be incorrectly diagnosed with another psychiatric or neurodevelopmental disorder potentially resulting in missed diagnosis of ADHD​[1,4,9]​.

Symptoms of ADHD can overlap or even co-exist with other psychiatric disorders, such as depression, anxiety, conduct disorder or bipolar disorder​[4,11]​. It is therefore important to identify and differentiate these comorbidities as they may affect treatment plans​[11]​. This can be achieved through detailed history taking, mental state examination and collateral information​[12]​. 

Patient counselling and support

Living with ADHD is challenging as the symptoms can significantly impair daily functioning. Once a diagnosis is made, the following advice may help improve quality of life for individuals and their support network​[7,9,13]​.

Encourage individuals and their support network to seek guidance and support from training programmes. For parents/carers this may include:

• Positive parent/carer child contact;
• Structure in the child or young person’s day;
• Clear and appropriate rules about behaviour and consistent management;
• Ensure parents/carers are aware that the above advice does not imply bad parenting and the aim is to optimise skills to meet the above average parenting needs;
• Advise individuals (or their parents/carers where appropriate) to discuss additional support/adjustments required with educational facilities/employers;
• Signpost individuals (and their families/carers) to further information and support, such as self-help, local and national support groups and voluntary organisations.