Growing up with ADHD: A study into long-term outcomes and their predictors

Abstract

Attention-deficit/hyperactivity disorder (ADHD) is a predominantly childhood-onset neurodevelopmental disorder. However, ADHD is not limited to childhood. The disorder has a highly heterogeneous developmental trajectory from childhood into adulthood, ranging from full remission to persistence of ADHD with adverse outcomes. The research in this thesis largely used data from the 18-year follow-up study of the IMAGE/NeuroIMAGE cohort. This follow-up successfully included 421 participants, among which adults (Mage = 28.84) with childhood ADHD (n = 154), their siblings (n = 138), and controls (n = 129). Outcomes collected at follow-up included 51 measures across 7 domains of functioning, including psychiatric status, behavioral and emotional problems, academic and professional functioning, adaptive functioning, neurocognitive functioning, physical health, and healthcare service use. Compared to their siblings and controls, adults with childhood ADHD showed worse long-term outcomes on more than 60% of the outcomes across the 7 domains of functioning, while their other outcomes were similar. Most group differences lay in the domains of behavioral and emotional problems, adaptive functioning, and neurocognitive functions. These negative outcomes seemed to be largely independent of a current ADHD diagnosis, as both the group with persistent ADHD and the group with remitted ADHD differed from the controls on the majority of outcomes. Siblings did not show an increased risk of negative outcomes. Among adults with a history of childhood ADHD, only 26% used ADHD medication in adulthood. Also, they were 3 to 7 times more likely to use neurological medications (analgesics and NSAIDs). Differences in medication use largely disappeared after adjusting for a current ADHD diagnosis or depression. Overall, differences between men and women were comparable to those observed in the general population; there was no evidence of a "double burden" of sex regarding ADHD. Our meta-analyses showed that a history of stimulant use was associated with an increased risk of ADHD persistence. Additionally, ADHD persistence was associated with an increased risk of depression and addiction. Our own machine-learning-based prediction models did not predict long-term ADHD outcomes any better than conventional logistic regression. Despite suboptimal performance, several potentially relevant predictors were identified: anxiety symptoms, autistic traits, and childhood motor coordination problems. The key takeaway is that the developmental trajectory into adulthood is heterogeneous and difficult to predict. While one group will achieve average adult functioning, adults with a childhood ADHD diagnosis have an elevated risk of difficulties, particularly psychiatric disorders and behavioral or emotional problems. In our sample, childhood stimulant use was not associated with long-term functional outcomes (assessed more than 10 years later).