This study was funded by Shire, now part of Takeda
ADHD in adulthood/adolescence is associated with a range of social and psychological impairments. ADHD can persist from childhood to adolescence in 55–66% of cases (Barkley et al. 2002; Faraone et al. 2006; Lara et al. 2009; Sibley et al. 2017). This study sought to identify factors which could predict the likelihood of persistent ADHD and the development of new-onset ADHD in adolescents. Prior to this study, diagnoses of conduct disorder (CD), measures of aggression and a familial history of ADHD were the most consistently reported factors that could predict whether ADHD would persist into adolescence; however, this work was largely carried out across North America. New-onset and persistent ADHD are understudied across Europe, and it is unknown if the North American studies are generalisable to European populations. This study aimed to address this by presenting 9-year follow-up results from a population of children in France.
The baseline cohort of 1012 children aged 6–12 years was identified in December 2008; firstly, 7912 French telephone numbers were randomly selected from a database of 18 million for a telephone interview designed to determine demographic characteristics, assess eligibility to participate* and obtain informed consent to participate in the study. Among those contacted, 4186 families were identified as eligible to participate, of whom 1012 were successfully recruited. The recruited parents responded to a questionnaire† adapted from the Kiddie Schedule for Affective Disorders and Schizophrenia, with questions pertaining to symptoms of ADHD, oppositional defiant disorder (ODD) and CD modified by the authors to address all Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5TM) criteria. Families were followed-up 9 years after the initial phone call was made, and a similar questionnaire administered, with the addition of questions to assess family history of ADHD; 492 (48.6%) of the original baseline sample responded to the follow-up questionnaire. The mean age of participants in this follow-up study was 18 years.
This study reported a 27.8% rate of ADHD persistence from childhood to adolescence; 16.7% of children diagnosed with ADHD at baseline also met full criteria for a diagnosis of ADHD at follow-up, with a further 11.1% meeting criteria for subthreshold‡ ADHD. In total, 1.1% of children not diagnosed with ADHD at baseline were diagnosed at follow-up, with an additional 1.5% meeting criteria for subthreshold ADHD.
The findings of the follow-up study were as follows:
Predictors of persistent ADHD
A comparison of participants who had been diagnosed with ADHD at baseline (n = 18) who did or did not persist with ADHD at follow-up found that:
- The mean (standard deviation [SD]) number of ADHD symptoms at baseline was significantly greater in persistent cases of ADHD than in resolved cases (13.7 [1.1] vs 8.6 [2.7]; p = 0.019), demonstrating that total number of ADHD symptoms at baseline significantly predicted persistence of ADHD.
- The mean (SD) number of baseline ODD symptoms was also significantly greater in persistent cases of ADHD than in resolved cases (4.3 [0.6] vs 1.2 [1.8]; p = 0.046). Additionally, diagnosis of ODD at baseline significantly predicted ADHD persistence (p = 0.017).
- Neither the number of baseline CD symptoms nor a diagnosis of CD at baseline significantly predicted persistent ADHD.
- There was no significant difference in the persistency of ADHD between those with a family history of adult ADHD or with a sibling diagnosed with ADHD and those without (both p = 0.386).
Predictors of new-onset ADHD
ADHD was classified as new-onset if participants who were not diagnosed with ADHD at baseline or at a 4-year follow-up were diagnosed at the 9-year follow-up. An analysis of factors predictive of new-onset ADHD at follow-up found that:
- New-onset ADHD was not more likely in those patients with subthreshold ADHD or a family history of adult ADHD (p = 0.464 and p = 0.231, respectively).
- Patients with new-onset ADHD at follow-up did not have more ADHD symptoms at baseline compared with those without new-onset ADHD.
- Mean (SD) number of inattentive symptoms at baseline was 0.4 (0.5) for those with full ADHD and 0.2 (0.4) for those with subthreshold ADHD, compared with 0.3 (0.9) for those who did not have ADHD at follow-up (p = 0.903).
- Mean (SD) number of hyperactive-impulsive symptoms at baseline was 0.4 (0.9) for those with full ADHD and 0 (0) for those with subthreshold ADHD, compared with 0.2 (0.7) for those who did not have ADHD at follow-up (p = 0.662).
- Mean (SD) number of total ADHD symptoms at baseline did not differ between individuals classified as having full ADHD (0.8 [1.3]), subthreshold ADHD (0.2 [0.4]) and not having ADHD (0.5 [1.4]) at 9-year follow-up (p = 0.749).
- Baseline ODD and CD diagnoses were good predictors of ADHD diagnosis at follow-up (p = 0.019 and p = 0.01). However, the mean (SD) number of ODD and CD symptoms at baseline did not differ between groups diagnosed with new-onset ADHD (ODD: 0 ; CD: 0.2 [0.4]), subthreshold ADHD (ODD: 0.7 [1.6]; CD: 0 ), and those not diagnosed with ADHD (ODD: 0.3 [0.9]; CD: 0.2 [0.8]) at follow-up (ODD: p = 0.510; CD: p = 0.792).
- For patients with new-onset full ADHD at Year 9, mean (SD) number of ODD symptoms (9.2 [6.2]) was significantly greater compared with those with subthreshold ADHD (5.3 [3.1]; p < 0.001) and those without ADHD (2.9 [2.0]; p = 0.007). Similarly, the mean (SD) number of CD symptoms in those diagnosed with new-onset full ADHD at Year 9 (3.8 [2.9]) was significantly higher than those diagnosed with subthreshold ADHD (2.5 [0.8]; p < 0.001) and those without ADHD (2.1 [0.5]; p < 0.001).
This study had some limitations; firstly, information about each child was collected via telephone interviews carried out with one adult, therefore the estimation of ADHD prevalence in the sample may have been affected by observer bias. Additionally, the number of children diagnosed at baseline with ADHD was small, and as a result the dataset for the persistence analysis was small, meaning that these results may not be generalisable to the wider population.
The authors concluded that childhood ADHD and ODD severity were the best predictors of ADHD persistence into adolescence; however, the previously reported finding of a familial link in persistent ADHD was not replicated in this study. The rate of persistence of ADHD into adolescence was lower in this study than previously reported, which may be a consequence of using a general, non-referred population, or a geographical effect. The authors suggested that, if results are replicated, subthreshold ADHD and symptoms of ODD in childhood should be monitored by physicians as these may be predictive of ADHD in adolescence.
Read more about persistent and new-onset ADHD here
*Eligibility criteria included having a child between the ages of 6 and 12 years, belonging to a demographic quota that had not been filled and having a telephone number still in service
†The questionnaire administered covered: the family’s living situation, the child’s school performance, symptoms and treatment history of ADHD, symptoms of ODD and CD, sleep disturbance, eating habits and use of iron supplements
‡Subthreshold ADHD was defined by modifying DSM-IV criteria to require only ≥3 inattentive or ≥3 hyperactive-impulsive symptoms
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