Results from three recent population-based longitudinal studies found that 67.5–90.0% of adults with symptoms of ADHD did not have childhood ADHD, which suggests the existence of adult-onset ADHD. It has been proposed that some individuals have subthreshold symptoms of ADHD in childhood, which later manifest in adulthood once certain social and educational supports are removed. Alternatively, it has also been proposed that adult-onset ADHD could be a misdiagnosis of another neurological or psychiatric disorder which mimics the symptoms of ADHD.
This French study involved patients (n=446; median age 33 years; 53.3% male) referred to a specialised adult ADHD outpatient clinic who underwent the Diagnostic Interview for ADHD in Adults* to assess current ADHD symptoms† and presence of ADHD symptoms in childhood.‡ Various parameters were assessed, including age at onset of ADHD symptoms, familial history of ADHD, educational level, psychiatric comorbidities (e.g. depression, bipolar disorder, substance-use disorder) and excessive daytime sleepiness using the self-report Epworth Sleepiness Scale (ESS).§
Within the clinical cohort assessed, 6.9% of patients (median age 36 years; 44.4% male) were classified as having adult-onset ADHD, including nine patients who had subthreshold ADHD symptoms in childhood (i.e. 4–5 symptoms of inattention or hyperactivity-impulsivity). On the other hand, 89.9% of patients (median age 33 years; 55.0% male) exhibited symptoms of ADHD in childhood, including 3.2% who developed ADHD symptoms between the ages of 12 and 17 years.
An age- and gender-matched comparison between patients with childhood- or adult-onset ADHD indicated that patients with adult-onset ADHD had a higher educational level, a lower frequency of being overweight (11.1% vs 31.5%; p=0.034), a greater inattentive presentation of ADHD (66.7% vs 41.7%; p=0.02), a less-severe Conners’ Adult ADHD Rating Scale index¥ (median [interquartile range (IQR)]: 66 [44–81] vs 75 [49–90]; p<0.001) and lower hyperactivity index (median [IQR]: 58 [32–78] vs 65 [36–83]; p<0.001) compared with patients who exhibited ADHD symptoms in childhood. There was no significant difference (p>0.05) in the incidence of familial history of ADHD, psychiatric comorbidity or substance use between patients with childhood- or adult-onset ADHD. The age of sleepiness onset in patients with a sleepiness complaint (ESS score >10/24) was significantly higher in patients with adult-onset ADHD (median [IQR]: 22.5 [15–45] vs 12.5 [5–42]; p=0.002), with the majority of patients with adult-onset ADHD having onset of sleepiness developing during adulthood. Although not significant, comorbid hypersomnolence disorder was also more likely to be found in patients with adult-onset ADHD (33.3% vs 17.6%; p=0.07).
Limitations of this study were reported to include the method of obtaining patient data, i.e. retrospective recall of disease onset within a clinical sample, and the fact that more severe cases of the disorder are not representative of a heterogeneous adult ADHD population.
The authors concluded that the frequency of adult-onset ADHD in a specialised adult ADHD outpatient clinic is less frequent than previously reported in the general population in other longitudinal studies. The study also highlighted the occurrence of hypersomnolence with adult-onset ADHD, suggesting that symptoms of sleepiness may be an alternative diagnosis for patients with no history of childhood ADHD. This study confirms the importance of excluding other disorders which may overlap with ADHD symptoms in the adult population.
Read more about adult-onset ADHD in clinical practice here
*The Diagnostic Interview for ADHD in Adults (DIVA-2) is a structured clinical interview used to assess the presence of ADHD symptoms in adulthood and childhood, in addition to the chronicity of these symptoms and the significant clinical or psychosocial impairments due to these symptoms. For this study, DIVA-2 was modified to fulfil the recent Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5TM) criteria for adult ADHD
†Patients with development of ≥5 symptoms of inattention or hyperactivity-impulsivity after the age of 18 were classed as having adult-onset ADHD
‡Childhood-onset ADHD was defined as ≥6 symptoms of inattention or hyperactivity-impulsivity before the age of 12, and ≥5 symptoms in adulthood with significant impairments in two areas of daily life within 6 months prior to the interview and in childhood
§The Epworth Sleepiness Scale (ESS) is a self-report questionnaire in which a score above 10/24 is indicative of clinically significant sleepiness. In this study, patients with a score >10 underwent a structured clinical interview to determine the age of sleepiness onset and the presence of hypersomnolence disorder according to DSM-5TM
¥The Conners’ Adult ADHD Rating Scale (CAARS) measures the presence and severity of ADHD symptoms, including inattention/memory problems, hyperactivity/restlessness, impulsivity/emotional lability and problems with self-concept
Lopez R, Micoulaud-Franchi J-A, Galera C, et al. Is adult-onset attention deficit/hyperactivity disorder frequent in clinical practice? Psychiatry Res 2017; 257: 238-241.