Identifying comorbid ADHD in autism: Attending to the inattentive presentation

There are high rates of comorbidity between ADHD and ASD; however, there has been limited work parsing rates by ADHD presentation. In addition, commonly used questionnaires have demonstrated reduced utility in capturing ADHD symptoms in individuals with ASD. We examined the prevalence of comorbid Attention-Deficit/Hyperactivity Disorder (ADHD) parsed by DSM-5 presentation in clinic-referred youth with Autism Spectrum Disorder (ASD) without intellectual disability (ID). We compared common rating scales to determine which most effectively identified comorbid ADHD. We examined comorbid ADHD diagnoses from archival assessment data for 419 youth with ASD without ID. We examined diagnostic discriminability of the parent and teacher ADHD Rating Scale (ADHD R-S), and Attention and ADH Problems Scales of the Child Behavior Checklist and Teacher Report Form using receiver operating characteristic (ROC) curves. Hierarchical logistic regression was used to examine measures’ unique contribution to ADHD diagnosis. Sixty-one percent of the study sample met DSM-5 criteria for an attention disorder. ADHD, Combined (ADHD-C) represented the largest proportion of ADHD diagnoses (76.8%), followed by Inattentive (ADHD-I;19.7%), Hyperactive/Impulsive (.02%), and Un-/Other Specified (.02%). Measures provided greater diagnostic discriminability in identifying ADHD-C relative to ADHD-I. The ADHD R-S inattentive symptom count provided the greatest discriminability for both subtypes and was the only scale that provided clinically meaningful differentiation between those with ASD only and ASD + ADHD-I. These results support using the ADHD R-S to capture comorbid ADHD symptoms in ASD. The findings underscore the need for more thorough examination of inattentive symptoms to rule out ADHD-I.