The majority of adults with ADHD have a diagnosed or undiagnosed comorbid psychiatric disorder, which can complicate diagnosis and treatment of ADHD.1-3
The US National Comorbidity Survey Replication found that adult Diagnostic and Statistical Manual of Mental Disorders – 4th Edition (DSM-IV) ADHD was highly comorbid with many other DSM-IV disorders in a large subsample of 18–44-year-olds (n=3199) in the US (Figure).4,5
Figure: Main comorbid psychiatric disorders in adult ADHD. Reproduced with kind permission from Kooij JJS et al. J Atten Disord 2012; 16(5 Suppl): 3S-19S.6
How does the aetiology and the pathology of ADHD vary across different patients? | Dr Matt McConkey | South Eastern Health and Social Care Trust, Northern Ireland, UK
Prevalence of ADHD with common psychiatric disorders
In a study of 2447 children and adolescents (aged 5–17 years) with ≥1 psychiatric disorder(s), 650 (27%) were diagnosed only with ADHD and 401 (16%) only with another psychiatric disorder, while 1396 (57%) had ≥2 psychiatric disorders (1269 [66%] also had ADHD).7
Figure: Psychiatric comorbidities in children and adolescents with and without ADHD. Reproduced with kind permission from Reale L et al. Eur Child Adolesc Psychiatry 2017; 26: 1443-1457.7
In a cross-sectional study of ADHD prevalence amongst 1986 adult psychiatric outpatients across Europe, the overall prevalence of Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5TM) ADHD was 15.3%.8*
- The most frequently reported comorbid psychiatric disorder in patients with ADHD was depression, which showed a lower prevalence in these patients compared with those without ADHD (40.3% vs 53.9%, respectively).8
- Anxiety showed a similar prevalence in patients with and without ADHD (36.4% vs 34.6%, respectively).8
- Alcohol abuse was more prevalent in patients with ADHD versus those without (10.3% vs 5.2%, respectively); however, alcohol dependence was comparable between groups (4.0% vs 4.9%, respectively).8
- Of those in the ADHD cohort, 11.5% were not diagnosed with a psychiatric comorbidity, compared with 3.4% of patients without ADHD.8
In a separate study, DSM-IV ADHD was diagnosed in 27 (22%) patients (n=124; aged 20–70 years) at four general adult psychiatry outpatient clinics in northeast England. In this study, patients had been diagnosed with a range of psychological disorders; however, those with an existing diagnosis of ADHD were excluded.9
- The most common pre-existing diagnosis in patients with newly diagnosed ADHD was depression (50% of men; 53% of women).9
- Anxiety (42% of men; 7% of women) and bipolar disorder (25% of men; 27% of women) were also common pre-existing disorders.9
- Of those with a diagnosis of ADHD, 71% reported having difficulties with mood or behaviour in childhood, compared with 26% of patients without a diagnosis of ADHD (p<0.05).9
- The Adult ADHD Self-Report Scale showed a significant correlation with the diagnosis of ADHD (kappa=0.60), but it misclassified 15 cases.9
- A positive score on the Wender Utah Rating Scale showed a significant correlation with the clinical diagnosis of ADHD (kappa=0.46), but 28 cases were misclassified.9
- When the criteria were changed to above the cut-off scores on both instruments, the correlation with the diagnosis of ADHD was increased (kappa=0.78), and 10 cases were misclassified, of which 8 were false positives.9
Figure: Overall prevalence of ADHD and selected psychiatric comorbidities in the US National Comorbidity Survey Replication. Table adapted from Kessler RC et al. Am J Psychiatry 2006; 163: 716-723.4
Lifetime prevalence of psychiatric comorbidities
Biederman et al. conducted a 10-year case-control prospective study of lifetime prevalence of comorbid psychopathology from adolescence into adulthood. At follow-up, 112 males with ADHD and 105 males without ADHD were successfully recalled, and 91% and 90% of individuals in the ADHD and control groups, respectively, had reached adulthood (aged ≥18 years). From the original ADHD cohort, 58% of patients had current full or subthreshold DSM-IV ADHD, compared with 6% in the control group (p<0.001).10
According to the study data, male patients with ADHD were significantly more likely to have:
- Major psychopathology (odds ratio [OR]: 6.1; 95% confidence interval [CI] 3.5–10.7)10
- Anxiety disorders (OR: 2.2; 95% CI 1.5–3.2)10
- Antisocial disorders (OR: 5.9; 95% CI 3.9–8.8)10
- Developmental disorders (OR: 2.5; 95% CI 1.7–3.6)10
- Substance-dependence disorders (OR: 2.0; 95% CI 1.3–3.0).10
A similar 11-year case-control study was conducted in females with (n=140) and without (n=122) ADHD. The risk of several psychopathologies was also significantly higher in females with ADHD compared with those without (p≤0.001).11
Female patients with ADHD were more likely to have:
- Mood disorders (hazard ratio [HR]: 6.8; 95% CI 3.7–12.6)11
- Anxiety disorders (HR: 2.1; 95% CI 1.6–2.9)11
- Antisocial disorders (HR: 7.2; 95% CI 4.0–12.7)11
- Developmental disorders (HR: 3.2; 95% CI 2.0–5.3)11
- Substance-dependence disorders (HR: 2.7; 95% CI 1.6–4.3)11
- Eating disorders (HR: 3.5; 95% CI 1.6–7.3).11
The lifetime prevalence for major depressive disorder, bipolar disorder, anxiety disorders (separation anxiety disorder, agoraphobia and social phobia), antisocial disorders (oppositional defiant disorder, conduct disorder and antisocial personality disorder), developmental disorders (tics/Tourette’s disorder and enuresis), and substance-abuse disorders (nicotine/alcohol/drug dependence) was significantly higher in males and females with DSM-IV ADHD than those without ADHD (p<0.05 for each).10,11
An analysis of the World Health Organization World Mental Health Surveys reported that 8.3% of 585 adults with ADHD had a comorbid mood (9.3%), anxiety (8.8%), substance-use (11.5%) or behavioural (15.6%) disorder. The highest rates of ADHD were seen in those with oppositional defiant disorder or adult antisocial behaviour disorder (35.5%), bipolar (15.2%), panic disorder (14.4%), social phobia (12.0%) and any substance use (11.5%).12
ADHD subtypes and psychiatric comorbidities
Several studies have investigated the variation in prevalence of psychiatric comorbidities in relation to different ADHD subtypes.13-15†
- Friedrichs et al. reported lower risks of generalised anxiety disorder and major depression for hyperactive-impulsive subtype ADHD compared with combined and inattentive subtypes.13
- Sprafkin et al. evaluated patterns of comorbidity associated with the different subtypes of ADHD. The majority of subgroup differences demonstrated that patients with combined subtype ADHD reported more severe comorbid symptoms versus hyperactive-impulsive and inattentive subtypes.14
- Wilens et al. reported higher rates of lifetime conduct disorder, antisocial disorder, major depression, bipolar disorder, psychosis and substance dependence in adults with combined subtype ADHD compared with the inattentive and hyperactive subtype.15
Gender and psychiatric comorbidities with ADHD
Some studies suggest that there are gender differences between ADHD and certain psychiatric comorbidities;16,17 however, other studies have reported no such differences when investigating some psychiatric comorbidities.13,17†‡
Evidence showing differences between men and women
- Rasmussen et al. reported significant differences between men and women for the frequency of affective disorders (28% vs 49% of patients, respectively), eating disorders (0% vs 6% of patients, respectively) and dyslexia (9% vs 4% of patients, respectively).16
- Anker et al. found significant differences between men and women in comorbid alcohol dependence (10.0% vs 4.0%, respectively), substance abuse (5.2% vs 0.7%, respectively), substance dependence (23.6% vs 9.4%, respectively) and bulimia/anorexia (1.1% vs 13.0%, respectively).17
Evidence showing no differences between men and women
- Friedrichs et al. reported no significant difference between genders in the increased risks of symptoms of generalised anxiety disorder, major depression, bipolar disorder, obsessive-compulsive disorder and alcohol dependence in 227 adults with DSM-IV ADHD.13
- Anker et al. also reported no significant differences between genders across major depression, suicidality, social phobia, agoraphobia, panic disorder, generalised anxiety disorder, post-traumatic stress disorder, alcohol abuse, obsessive-compulsive disorder, bipolar disorder and psychotic disorder.17
*An observational study conducted in adult patients attending centres delivering general psychiatric care in Austria, Belgium, Denmark, Germany, The Netherlands, Spain, Sweden and the UK. Of the 5662 outpatients attending the study centres, 2284 were included in the study. The primary objective was to estimate the prevalence of DSM-5TM ADHD and psychiatric comorbid conditions8
†Friedrichs et al. recruited participants from the Swedish Twin Registry; 17,899 individuals aged 20–47 years provided information about ADHD diagnosis or symptoms via the web study page or telephone interview. Information about ADHD symptoms was collected using a self-report questionnaire based on the DSM-IV items. ADHD combined subtype was reported in 26 (0.15%) individuals, hyperactive-impulsive subtype in 125 (0.70%) individuals and inattentive subtype in 76 (0.42%) individuals.13 Sprafkin et al. included patients with ADHD (aged 18–75 years) from a mental health outpatients clinic (n=487) and a community sample (n=900) in Suffolk County, New York, who completed a DSM-IV-referenced rating scale and a questionnaire (social, educational, occupational and treatment variables). In the community sample, 28 (3.1%) patients had the inattentive subtype, 18 (2.0%) had the hyperactive-impulsive subtype, 14 (1.6%) had the combined subtype and 840 (93.3%) did not meet the criteria for ADHD. In the clinic sample, 284 (58.3%) patients did not have ADHD whereas 97 (19.9%), 32 (6.6%) and 74 (15.2%) patients met the criteria for the inattentive, hyperactive-impulsive and combined subtype, respectively.14 Wilens et al. included 107 adult outpatients with ADHD; 66 (62%) had combined subtype, 33 (31%) had inattentive subtype and 8 (7%) had hyperactive-impulsive subtype. Participants were recruited through advertisements in the greater Boston area and from referrals to adult ADHD clinics. All adults were interviewed using the Structured Clinical Interview for DSM-IV and modules from the Schedule for Affective Disorders and Schizophrenia for School-Age Children Epidemiologic Version15
‡Rasmussen et al. reviewed data from 600 consecutive patients (men, n=436; women, n=164) aged 17–57 years with ADHD, referred to receive pharmacological treatment for ADHD during a 7-year period in Norway. The majority of patients had the combined form of ADHD (67% of men and 69% of women), 2.2% of men and 2.1% of women had the hyperactive-impulsive subtype, and the remaining patients (26% of men and 23% of women) had the inattentive subtype.16 Anker et al. analysed 548 adults diagnosed with ADHD in a cross-sectional study (men, n=271; women, n=277). Just over half of men (52.4%) and women (54.5%) had ≥1 comorbid psychiatric disorder(s), and 21.0% of men and 25.3% of women had ≥2 comorbid psychiatric disorders17
- Canadian ADHD Resource Alliance (CADDRA). Canadian ADHD Practice Guidelines. Fourth Edition. Toronto, ON; CADDRA, 2018.
- Kooij JJS, Bijlenga D, Salerno L, et al. Updated European Consensus Statement on diagnosis and treatment of adult ADHD. Eur Psychiatry 2019; 56: 14-34.
- NICE guideline 2018. Attention deficit hyperactivity disorder: diagnosis and management. Available at: https://www.nice.org.uk/guidance/ng87. Accessed December 2018.
- Kessler RC, Adler L, Barkley R, et al. The prevalence and correlates of adult ADHD in the United States: results from the National Comorbidity Survey Replication. Am J Psychiatry 2006; 163: 716-723.
- Kessler RC, Berglund P, Chiu WT, et al. The US National Comorbidity Survey Replication (NCS-R): design and field procedures. Int J Methods Psychiatr Res 2004; 13: 69-92.
- Kooij JJ, Huss M, Asherson P, et al. Distinguishing comorbidity and successful management of adult ADHD. J Atten Disord 2012; 16(5 Suppl): 3S-19S.
- Reale L, Bartoli B, Cartabia M, et al. Comorbidity prevalence and treatment outcome in children and adolescents with ADHD. Eur Child Adolesc Psychiatry 2017; 26: 1443-1457.
- Deberdt W, Thome J, Lebrec J, et al. Prevalence of ADHD in nonpsychotic adult psychiatric care (ADPSYC): a multinational cross-sectional study in Europe. BMC Psychiatry 2015; 15: 242.
- Rao P, Place M. Prevalence of ADHD in four general adult outpatient clinics in North East England. Prog Neurol Psychiatry 2011; 15: 7-10.
- Biederman J, Monuteaux MC, Mick E, et al. Young adult outcome of attention deficit hyperactivity disorder: a controlled 10-year follow-up study. Psychol Med 2006; 36: 167-179.
- Biederman J, Petty CR, Monuteaux MC, et al. Adult psychiatric outcomes of girls with attention deficit hyperactivity disorder: 11-year follow-up in a longitudinal case-control study. Am J Psychiatry 2010; 167: 409-417.
- Fayyad J, Sampson NA, Hwang I, et al. The descriptive epidemiology of DSM-IV Adult ADHD in the World Health Organization World Mental Health Surveys. Atten Defic Hyperact Disord 2017; 9: 47-65.
- Friedrichs B, Igl W, Larsson H, et al. Coexisting psychiatric problems and stressful life events in adults with symptoms of ADHD–a large Swedish population-based study of twins. J Atten Disord 2012; 16: 13-22.
- Sprafkin J, Gadow KD, Weiss MD, et al. Psychiatric comorbidity in ADHD symptom subtypes in clinic and community adults. J Atten Disord 2007; 11: 114-124.
- Wilens TE, Biederman J, Faraone SV, et al. Presenting ADHD symptoms, subtypes, and comorbid disorders in clinically referred adults with ADHD. J Clin Psychiatry 2009; 70: 1557-1562.
- Rasmussen K, Levander S. Untreated ADHD in adults: are there sex differences in symptoms, comorbidity, and impairment? J Atten Disord 2009; 12: 353-360.
- Anker E, Bendiksen B, Heir T. Comorbid psychiatric disorders in a clinical sample of adults with ADHD, and associations with education, work and social characteristics: a cross-sectional study. BMJ Open 2018; 8: e019700.