Epidemiology and prognosis
Epidemiological studies suggest that the prevalence of attention-deficit hyperactivity disorder (ADHD) in the general adult population ranges from 2 to 5%. Among adults with a common psychiatric condition who are already accessing mental health services, it is as high as 10–20% (Kooij Reference Kooij, Bejerot and Blackwell2010). Some of the adverse consequences of untreated ADHD are increased rates of substance misuse, unemployment, criminality, relationship breakdown and driving accidents. Once diagnosed, ADHD is a treatable condition that responds well to pharmacological treatment. First-line treatment options for adults have been shown to have an effect size of 0.6–0.9, which is significantly high compared with other commonly used psychiatric medications, such as antidepressants (effect size 0.3–0.5) (Leucht Reference Leucht, Hierl and Kissling2012).
Diagnostic criteria of ADHD
ADHD is a persistent, pervasive disorder characterised by symptoms of inattention, impulsivity and hyperactivity. As a result of their inattentive symptoms, adults with ADHD may typically experience difficulties with day-to-day organisation, poor time-keeping, forgetfulness and making careless mistakes. Symptoms of hyperactivity–impulsivity may result in difficulties with money management, impatient behaviour, speaking or acting without thinking and excessive physical or mental activity. For adults to receive a diagnosis of ADHD, DSM-5 criteria require that five or more symptoms of inattention and/or hyperactivity–impulsivity must be present (American Psychiatric Association 2013). Note that this is lower than the six or more symptoms of inattention and/or hyperactivity–impulsivity that are required for a diagnosis of ADHD in childhood. Symptoms must have persisted for at least 6 months and have had a negative impact on social and academic/occupational functioning.
Several of the symptoms must have been present before 12 years of age, they must be present in two or more settings and must not be better explained by another mental disorder.
Now we look at some possible reasons why ADHD in adults is ‘missed’ or misdiagnosed.
Factors that may result in ADHD being missed as a diagnosis
Lack of awareness among clinicians
Previously, ADHD was considered to be a childhood disorder that improved with age, but it is now recognised to persist into adulthood in 50–66% of individuals, resulting in ongoing clinical and psychosocial impairment (Barkley Reference Barkley, Fischer and Smallish2002; Lara Reference Lara, Fayyad and de Graaf2009). However, many clinicians are still not aware that ADHD is a valid diagnosis in adults.
Some also believe that hyperactivity symptoms must be present for a diagnosis, resulting in those who present with predominantly inattentive symptoms being overlooked. ADHD prevalence is higher in men than in women (1.6:1) (Willcutt Reference Willcutt2012) and it has been suggested that this may be because women are more likely to present with predominantly inattentive symptoms and therefore not be diagnosed. Furthermore, some patients with ADHD have a tendency to hyper-focus on tasks that they are interested in and this may also mislead clinicians into believing that problems with concentration are absent.
Stigma
Adults with ADHD have often had to endure lifelong difficulties and may feel that they have grossly underachieved for their potential, resulting in low self-esteem. Many of them want to avoid being ‘labelled’ with a psychiatric diagnosis and have considerable anxieties about having to take medications to feel ‘normal’. This may result in them avoiding seeking help from professionals.
Masking and/or self-medicating of symptoms
Adults with ADHD may develop ways of compensating for their lifelong difficulties. Examples include pursuing a career that is fast paced, varied or involves physically demanding work. They may also have a partner or spouse who compensates for their organisational difficulties. Many adults who have undiagnosed ADHD resort to ‘self-medicating’ their symptoms with caffeine, alcohol or illicit drugs such as cannabis, cocaine or amphetamines.
Factors that may result in misdiagnosis
Age-related change in symptoms
The symptoms of hyperactivity often seen in childhood may be more likely to manifest as inner restlessness, overtalkativeness or inability to relax in adulthood. A significant number of adults with ADHD also experience symptoms of emotional dysregulation, with frequent mood changes throughout the day, low tolerance to frustration and temper outbursts that may be misinterpreted as a mood or personality disorder.
Overlapping symptoms and comorbidity
Symptoms of ADHD such as poor concentration, physical restlessness, impulsivity and mood lability overlap with symptoms of depression, anxiety, bipolar affective disorder and borderline personality disorder, which can result in an incorrect diagnosis being made.
ADHD is a highly comorbid condition, with 75% of adults with ADHD having at least one other psychiatric diagnosis (Kooij Reference Kooij, Bejerot and Blackwell2010). These include mood disorders, anxiety, personality disorder and substance misuse. Often, it is the comorbid conditions that are recognised and the symptoms of ADHD that are missed.
Conclusions
There are several patient- and clinician-related reasons why ADHD may be missed or misdiagnosed in adults, but to ensure that patients access appropriate and timely support/treatment it is important that ADHD is considered as a possible diagnosis. Readers further interested in the assessment and treatment of adult ADHD are directed to resources listed in Box 1.
BOX 1 Further reading resources
Johnson J, Morris S, George S (2020) Attention deficit hyperactivity disorder in adults: what the non-specialist needs to know. British Journal of Hospital Medicine, 81(3): 1–11.
National Institute for Health and Care Excellence (2018) Attention Deficit Hyperactivity Disorder: Diagnosis and Management (NICE Guideline NG87). NICE.
Royal College of Psychiatrists’ webpage ‘ADHD in Adults’: www.rcpsych.ac.uk/mental-health/problems-disorders/adhd-in-adults
UK Adult ADHD Network (UKAAN) website: www.ukaan.org
Author contributions
All three authors contributed to the conception of the idea, writing and revising the manuscript.
Declaration of interest
J.J. has received honoraria for talks at training events supported by the following pharmaceutical companies: Janssen, Flynn and Takeda/Shire. S.M. works as a pharmacist independent prescriber in both National Health Service and private adult ADHD clinics; she has been on an advisory board for Shire Pharmaceuticals, has received honoraria for delivering a talk on the treatment of ADHD for Flynn Pharmaceuticals and Takeda, and has received sponsorship from both companies to attend educational and training events on adult ADHD.
ICMJE forms are in the supplementary material, available online at https://doi.org/10.1192/bja.2020.34.
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