The rates of ADHD persistence from childhood to adulthood are highly variable across literature reports. In addition, the conventional understanding that adult ADHD is a childhood-onset illness has been challenged by recent findings pointing to an adult-onset form of the illness. This review attempts to address these conflicting reports by shedding light on the following points:
- Conceptual and methodological issues associated with the evaluation of ADHD trajectories
- Estimations of persistence rates and its predictors
- Long-term negative outcomes of childhood ADHD and their predictors
- Adult-onset ADHD and its predictors.
One key methodological factor underlying the variability in ADHD persistence rates is the inconsistency of diagnostic criteria used to derive the ADHD diagnosis at baseline and at follow-up within and across studies. Another factor contributing to the variability of persistence rates is the disparity among studies with respect to the level and source of the impairment criterion required for establishing the ADHD diagnosis. Furthermore, the heterogeneity of samples (community vs clinical), demographic aspects (differences in age of assessment and female to male ratio in the study sample) and source of information (parent- vs teacher-report for childhood ADHD diagnosis) across studies may also explain the disagreement of the literature estimates of ADHD persistence.
The lowest reported ADHD persistence rate is 4%. The male-only composition of the US study sample, the use of different diagnostic systems at baseline and follow-up, the requirement of endorsement of ADHD symptoms/impairment at follow-up, and the reliance on a Diagnostic and Statistical Manual of Mental Disorders threshold as opposed to a norm-based approach all constitute potential sources for this low estimate. The highest prevalence of ADHD persistence (76%) can be explained by factors including the short follow-up time, the consistency in diagnostic tools used at baseline and follow-up, the UK study sample comprising patients with ADHD combined subtype only, and the relatively young age at follow-up. The most consistent risk factors associated with persistence are: comorbid conditions including conduct disorder and depression, severe ADHD and ADHD treatment.
A substantial body of evidence demonstrates that adults with persistent ADHD are at a disadvantage in multiple life domains* relative to those without ADHD. Multiple factors have been proposed as childhood predictors of adverse ADHD outcomes in adulthood, including ADHD severity, comorbidity profile, prenatal, genetic and familial factors, and gene–environment interactions. Exercising and cognitive abilities are suggested to be protective factors.
The findings of recent studies conducted in Brazil, New Zealand and the UK have converged to suggest that ADHD might also arise during adulthood. However, the plausibility of these conclusions have been questioned, and the findings have been ascribed to the shift from parent- or teacher-report in childhood to self-report in adulthood. Although some childhood predictors of adult-onset ADHD have been identified, more research is needed to further elucidate predictive factors for the adult-onset form of ADHD.
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*Lower academic achievements; higher unemployment rates; lower income; higher likelihood of emergence of substance-use disorders and personality disorders; and increased risk of traffic accidents
Caye A, Swanson J, Thapar A, et al. Life span studies of ADHD – conceptual challenges and predictors of persistence and outcome. Curr Psychiatry Rep 2016; 18: 111.