Differing Anxiety Levels in Youth with Autism Spectrum Disorder, Attention-Deficit Hyperactivity Disorder, and Both Diagnoses

Background: Attention-Deficit/Hyperactivity Disorder (ADHD) is a common co-occurring neurodevelopmental disorder among youth with autism spectrum disorder (ASD; Lanes et al. 2016). Both children with ADHD or ASD individually, and those with comorbid ADHD and ASD, experience higher rates of total anxiety compared to typically developing (TD) peers (Bauermeister et al. 2007; White et al 2009; Wood & Gadow 2010), which impacts treatment response (Antshel et al., 2011; March et al., 2000). ASD youth often experience separation anxiety (van Steensel et al., 2011), social anxiety and generalized anxiety symptoms, while ADHD youth typically report heightened separation and generalized anxiety (Tsang et al., 2012). Therefore, there is reason to believe that ADHD and ASD may confer differential and conjoint risk for specific anxiety symptoms in youth. No study to date has examined the relative impact of having comorbid ASD and ADHD on specific anxiety symptoms in youth.

Objectives: This study investigates relationships between anxiety, ADHD, and ASD in order to determine if this co-morbidity can affect the presentation of anxiety. It was hypothesized that youth with comorbid ADHD and ASD would experience higher levels of overall anxiety, specifically separation, generalized, and social anxiety symptoms, compared to TD youth and youth with only one of the two disorders.

Methods: 86 participants (M_age = 13.71, SD_age = 1.83, 63 male) were divided into one of four diagnostic groups (Table 1). The ASD group met the criteria on the ADOS-2 (Lord et al., 2012). Youth who met criteria for ADHD exceeded the ADHD combined-type clinical cutoff on the parent-reported CASI-5 (Gadow & Sprafkin, 2013). Participants and their parents completed a measure of anxiety (MASC-2; March, 2013). One-way ANOVA was used to compare mean anxiety across groups.

Results: ASD+ADHD (M=60.13) and ASD only (M=59.17) groups had higher total parent-reported overall anxiety than the TD group (M=51.41; p=.050; see Figure 1). Both the ASD (M=58.70) and ADHD (M=66.50) groups self-reported greater overall anxiety than the TD group (M=51.66; p=.04). Regarding specific anxiety symptoms, parent-reported separation anxiety was higher in the ASD+ADHD group (M=60.04) than the ASD (M=53.03) and TD (M=51.31) groups, and in the ADHD group (M=64.50) than the TD group (p=.03). Self-reported separation anxiety was higher in the ADHD group (M=73.00) than the ASD+ADHD (M=59.22) and ASD groups (M=57.90), all of which were higher than TD (M=50.45) youth (p<.001). Neither parent- nor self-reported generalized anxiety or social anxiety symptoms differed significantly between groups (all p>.15).

Conclusions: Parents reported higher separation anxiety symptoms in the ASD+ADHD group relative to all other groups, while youth with ADHD reported themselves to experience higher levels of separation anxiety in comparison to other groups. When comparing individuals with ASD and ADHD separately, ADHD was particularly associated with co-occurring separation anxiety. Overall, ASD and ADHD both confer risk for anxiety in youth, but those with ADHD may be more likely to develop separation anxiety over other types of anxiety. Our results have implications for the nosology, taxonomy, and etiopathology of these common complex comorbidities in youth.