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2 Feb 2018

Shaw P. Am J Psychiatry 2018; 175: 95-96

Prospective studies in the 1990s showed that approximately 15–20% of children with ADHD continued to present with ADHD symptoms into adulthood, and more recent studies have reported that ADHD can have an onset in adolescence or adulthood, referred to by the authors as late-onset ADHD. This has led to a change in the perception that ADHD is a neurodevelopmental disorder only associated with childhood. This review article highlights the differences in reported prevalence of late-onset ADHD between studies.

A recent study by Sibley et al (2018)1 examined data from a group of children who constituted a comparison group in the well-known Multimodal Treatment of ADHD (MTA) study and initially presented without ADHD. This childhood cohort underwent regular clinical assessments into early adulthood, and Sibley et al found that during adolescence, 40% of these participants screened positive for ADHD and 20% presented with ADHD in adulthood. However, applying constraints on the data reduced the apparent prevalence of late-onset ADHD to 3.3%. The constraints applied required that: symptoms must cause impairments across multiple contexts; symptoms must not be better explained by substance misuse or a psychiatric disorder; and symptom onset must have occurred at ≥12 years of age. Exclusion of childhood symptoms that fell near the diagnostic threshold further reduced the reported prevalence of late-onset ADHD to 2%. The prevalence of late-onset ADHD reported by Sibley et al is comparable with that reported by the Dunedin birth cohort study conducted in New Zealand,2 which followed participants into middle age. In this study, the prevalence of adult-onset ADHD was reported to be 2.7%; however, in the United Kingdom, the Environmental Risk Longitudinal Twin Study3 reported a prevalence of late-onset ADHD of 5.5%, and in the Brazilian Pelotas Birth Cohort Study,4 the prevalence estimate of late-onset ADHD was 6.3% once substance misuse and other psychiatric disorders were accounted for.

It is unclear why variable prevalence estimates of late-onset ADHD have been reported, given that each of these studies was well designed and carefully conducted. In the study by Sibley et al, the children who initially presented without ADHD were gender-matched comparisons to the MTA study ADHD cohort, and were therefore predominantly male, since childhood ADHD is more common in males. Interestingly, late-onset ADHD has been reported to either have an equal distribution between males and females or to be more common in females. Therefore, to account for this, the Sibley et al study findings may require an adjustment before the estimated 2% prevalence of late-onset ADHD can be extrapolated to the general population. Moreover, the birth cohort studies contained thousands of participants, compared with hundreds of participants in the Sibley et al study, and these larger sample sizes may allow the precision of the estimated prevalence and the risk of late-onset ADHD to be calculated. In addition, differences in the primary source of diagnostic information (e.g. participant alone, parents, teachers and clinicians) to diagnose childhood and late-onset ADHD between studies may have contributed to the differences in estimated prevalence of late-onset ADHD.

The authors concluded that a definitive prevalence of late-onset ADHD cannot be established from these studies, but that there appears to be a notable prevalence of late-onset ADHD of 2–3% that is not better attributed to a substance-use disorder or another psychiatric disorder. Results from these studies indicate a need for future research into late-onset ADHD and highlight a potential public health challenge, wherein young adults are presenting to services for the first time with ADHD-related symptoms.

Read more about the variation in reported prevalence of late-onset ADHD here

 

1. Sibley MH, Rohde LA, Swanson JM, et al. Late-onset ADHD reconsidered with comprehensive repeated assessments between ages 10 and 25. Am J Psychiatry 2018; 175: 140-149
2. Moffitt TE, Houts R, Asherson P, et al. Is adult ADHD a childhood-onset neurodevelopmental disorder? Evidence from a four-decade longitudinal cohort study. Am J Psychiatry 2015; 172: 967-977
3. Agnew-Blais JC, Polanczyk G, Danese A, et al. Persistence, remission and emergence of ADHD in young adulthood: results from a longitudinal, prospective population-based cohort. JAMA Psychiatry 2016; 73: 713-720
4. Caye A, Rocha TB, Anselmi L, et al. Attention-deficit/hyperactivity disorder trajectories from childhood to young adulthood: evidence from a birth cohort supporting a late-onset syndrome. JAMA Psychiatry 2016; 73: 705-712

Shaw P. Growing up: evolving concepts of adult attention deficit hyperactivity disorder. Am J Psychiatry 2018; 175: 95-96.

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