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Three key features define attention-deficit hyperactivity disorder (ADHD) or hyperkinetic disorder (HKD):1,2

  • Inattention
  • Hyperactivity
  • Impulsivity.

The contribution of each to an individual’s presentation of ADHD varies from patient to patient.1 In some individuals, two or more features may contribute in equal measure; in others, one feature may predominate.1

How do the symptoms of ADHD change across the lifespan? | Dr David Coghill | Royal Children’s Hospital, Melbourne, Australia

How much does the disease presentation of ADHD vary between different patients? | Dr Joel Young | Rochester Centre for Behavioral Medicine, Michigan, USA

As different features of ADHD can impair functioning and quality of life in different ways,3-6 it is important to accurately evaluate each patient’s unique symptomatic characteristics, using medical classification systems such as the Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5TM) or the International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10).1,2 Whereas the ICD-10 characterises HKD by its ‘cardinal features’ of impaired inattention and overactivity,2 the DSM-5TM categorises patients with ADHD by three main presentations: combined type, predominantly inattentive type and predominantly hyperactive-impulsive type.1


Inattention is characterised as an individual moving between tasks without completing any one activity, seemingly losing interest in one task because they become diverted to another.1,2 Individuals with inattention are often easily distracted and forgetful, and experience difficulties when organising activities.1,2


Hyperactivity refers to excessive motor activity,1,2 and may present differently depending on the individual’s age.1


Individuals with impulsive tendencies can be reckless and appear impatient, and are often disinhibited in social situations. They may find it difficult to wait their turn, intruding on or interrupting others’ activities or blurting out answers to a question before it has been completed.1,2

ADHD and psychiatric comorbidities

Symptoms of ADHD can overlap with those of other related disorders. Therefore, care in differential diagnosis is needed. When there are coexisting psychiatric conditions, it is important to try and differentiate the level of impairment due to ADHD, because this will guide the treatment plan.7

Common coexisting conditions in children with ADHD include disorders of mood, conduct, learning, motor control, language and communication and anxiety disorders (Figure). Adults with ADHD may also commonly have personality disorders, bipolar disorder, obsessive-compulsive disorder and substance misuse (Figure).7

Figure: ADHD and psychiatric comorbidities in children and adolescents: descriptive overlapping and distinct features. Figure developed using information from CADDRA guidelines 2018.8 Note that these are examples only and not an exhaustive list.

ADHD and psychiatric comorbidities in children and adolescents: descriptive overlapping and distinct features


Figure: ADHD and psychiatric comorbidities in adults: descriptive overlapping and distinctive features. Reproduced with kind permission from Katzman MA et al. BMC Psychiatry 2017; 17: 302.9*

ADHD and psychiatric comorbidities in adults: descriptive overlapping and distinctive features


*A review by Katzman et al. discussed the most frequent comorbid psychopathologies, mood and anxiety disorders, substance-use disorders and personality disorders, and the challenges presented for diagnosis and treatment due to overlapping symptoms of ADHD and psychiatric comorbidities in adults. The review went on to discuss that this overlap between disorders has led to the proposal that diagnosis and treatment of ADHD may be considered on a spectrum using a dimensional rather than a categorical approach.9

  1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. 2013.
  2. World Health Organization. The ICD-10 Classification of Mental and Behavioural Disorders. Available at: Last updated 1993; 1: 1-263. Accessed February 2019.
  3. Caci H, Asherson P, Donfrancesco R, et al. Daily life impairments associated with childhood/adolescent attention-deficit/hyperactivity disorder as recalled by adults: results from the European Lifetime Impairment Survey. CNS Spectr 2015; 20: 112-121.
  4. Gudjonsson GH, Sigurdsson JF, Eyjolfsdottir GA, et al. The relationship between satisfaction with life, ADHD symptoms, and associated problems among university students. J Atten Disord 2009; 12: 507-515.
  5. O’Callaghan P, Sharma D. Severity of symptoms and quality of life in medical students with ADHD. J Atten Disord 2014; 18: 654-658.
  6. Grenwald-Mayes G. Relationship between current quality of life and family of origin dynamics for college students with attention-deficit/hyperactivity disorder. J Atten Disord 2002; 5: 211-222.
  7. NICE guideline 2018. Attention deficit hyperactivity disorder: diagnosis and management. Available at: Accessed February 2019.
  8. Canadian ADHD Resource Alliance (CADDRA). Canadian ADHD Practice Guidelines. Fourth Edition. Toronto, ON; CADDRA, 2018.
  9. Katzman MA, Bilkey TS, Chokka PR, et al. Adult ADHD and comorbid disorders: clinical implications of a dimensional approach. BMC Psychiatry 2017; 17: 302.
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