Profiles and Outcomes of Comorbid ASD and ADHD from Childhood to Adulthood (From ages 6 through 25)

Background:  With prevalence estimates ranging from 31 to 78%, Attention-Deficit/Hyperactivity Disorder (ADHD) is one of the most commonly co-occurring conditions in ASD (Ponde, Novaes, & Losapio, 2010).  Existing literature is lacking in clarity as to whether children with ASD and ADHD have a unique profile and differential outcomes compared to their counterparts without ADHD.  In particular, the appropriateness of stimulant medication as treatment for ADHD symptoms in ASD is still under debate (Frazier et al., 2011).  Gaining a clear understanding of factors that contribute to adult outcomes in this population would be an important step to optimizing their potential. 

Objectives:  The present study examined (1) childhood profiles and adult outcomes of co-morbid ASD and ADHD (ADHD+), compared to ASD without ADHD (ADHD-) and (2) predictors of secondary and postsecondary outcomes.  Based on the prevalent assumption that the additional burden of ADHD would lead to increased distress and functional impairment, we hypothesized that ADHD+ compared to ADHD- would yield poorer social skills and academic achievement in childhood and employment/college enrollment in adulthood.

Methods: Secondary data analysis was conducted on two separate yet closely related longitudinal datasets: Special Education Elementary Longitudinal Study (SEELS) and the National Longitudinal Transition Study-2 (NLTS2).  These datasets comprise nationally representative samples of youth who received special education services in the U.S. (ages 6-17 and ages 13-25 respectively).  The sample for this study was reduced to those with the primary diagnosis of ASD who were capable of producing valid standard academic achievement scores, which naturally limited the inclusion of most individuals with intellectual disability (n=340 in SEELS; n=473 in NLTS2). 

Results: 15% of the sample had the additional diagnosis of ADHD at age seven; the rate steadily increased until it peaked at 33% around age 13 and then plateaued into adulthood.  When the ADHD+ and ADHD- groups were compared across childhood characteristics (see Table 1), no statistically significant differences emerged in terms of gender, race, and income.  ADHD+ outperformed their ADHD- counterparts on academic achievement measures in SEELS (children), especially in language arts; no statistical differences were found in NLTS2 (adolescents).  Predictors of academic success portrayed a complex picture.  Having ADHD itself did not seem to have a significant effect when other factors such as gender, income, and medication use were considered.  Detailed results will be discussed in the final report.  Childhood academic achievement was determined to be a highly significant predictor of adult outcomes for both groups (see Table 2).  ADHD diagnosis was also a strong predictor of adult outcomes, with ADHD+ group demonstrating significantly lower rates of employment and postsecondary education enrollment.  However, controlling for academic achievement, there was a strong interaction effect between having a dual diagnosis of ADHD and using ADHD medication, such that those who used ADHD medication (given an ADHD diagnosis) experienced similar odds of success regarding adult outcomes as the ADHD- group.

Conclusions:   These results suggest that rather than experiencing a simple additive adverse effect of comorbid ADHD, ADHD+ group may experience differential outcomes depending on ADHD medication and other factors.