Comorbid Anxiety and ADHD Differentially Impact Clinical Presentation in Preschoolers with Autism

Background: Psychiatric comorbidities are common in individuals with autism spectrum disorder (ASD). Two of the most prevalent comorbidities are anxiety and ADHD. Approximately 40-60% of children with ASD meet criteria for one or both of these disorders. The presence of these comorbid diagnoses has been linked to more severe social deficits and repetitive behaviors, increased sensory challenges, and higher levels of irritability. Despite their high prevalence, relatively little is known about how comorbid anxiety and ADHD diagnoses differentially influence clinical presentation in young children with ASD.

Objectives: Using parent-report measures, we aimed to understand how comorbid anxiety and ADHD impact clinical presentation in children with ASD.

Methods: Sixty-nine 3-6-year-old children with ASD participated in this study. Anxiety disorders and ADHD were assessed through parent interview using the Preschool Age Psychiatric Assessment (PAPA). We hypothesized that meeting criteria for any anxiety disorder and ADHD on the PAPA would be differentially associated with higher ASD symptom severity (ADOS-2 severity scores), increased severity within different domains of repetitive behaviors (e.g. ritualistic behaviors, stereotyped motor behaviors, sensory features; Repetitive Behavior Scale-Revised subscale scores and Sensory Experiences Questionnaire), and higher levels of irritability (Aberrant Behavior Checklist). To explore the impact of multiple comorbidities on the functioning of children with ASD, we used an additive main effect general linear model. This method provides marginal predictions for both anxiety and ADHD on the outcomes of interest. This approach accounts for non-independence between groups, given that some children have both anxiety and ADHD, and identifies the unique contribution of anxiety and ADHD on each outcome.

Results: Based on the PAPA, 87% of children met criteria for ADHD, anxiety, or anxiety+ADHD. Specifically, 16% of our sample met criteria for ADHD only, 26% met criteria for anxiety only, and 45% met criteria for ADHD+anxiety. When both anxiety and ADHD diagnoses were included in the same model, anxiety (F(1)=4.6, p=0.04), but not ADHD (F(1)=0.89, p=0.3), was associated with increased overall ASD symptom severity as measured with the ADOS-2 severity score. In analyses using the RBS-R subdomain scores to assess repetitive behaviors, ADHD was found to be uniquely associated with increased self-injurious behavior (F(1)=4.4, p=0.04), whereas anxiety was uniquely associated with increased ritualistic (F(1)=10.15, p<0.01) and sameness behaviors (F(1)=3.97, p=0.05). Neither anxiety nor ADHD were associated with stereotyped motor, compulsive, or restricted behaviors. With regard to associated features of ASD, comorbid anxiety (F(1)= 16.5, p<0.001), but not ADHD (F(1)=0.27, p=0.6), was associated with increased sensory over-responsivity. In contrast, comorbid ADHD (F(1)=7.27, p<0.01), but not anxiety (F(1)=0.89, p=0.4), was associated with increased irritability.

Conclusions: Preschoolers with ASD have high levels of psychiatric comorbidity, with anxiety and ADHD particularly prevalent. The presence of these comorbidities significantly and differentially impacts the clinical presentation in children with ASD. These results suggest that comorbid psychiatric disorders may not only contribute to the clinical heterogeneity inherent in ASD, but may also impact the diagnosis and treatment of the disorder.