Differentiating Autism Spectrum Disorder from ADHD

Core Distinguishing Features

The American Academy of Pediatrics recommends distinguishing ASD from ADHD by focusing on core social-communication deficits and the quality of repetitive behaviors, as children with ASD demonstrate fundamental impairments in joint attention, nonverbal communication, and social reciprocity that are absent in pure ADHD, while their repetitive behaviors serve self-regulatory functions rather than being driven by impulsivity 1, 2
Failure to respond to name at 12 months is highly specific for ASD, distinguishing it from other developmental delays including ADHD, with 86% specificity 1, 2
Deficits in joint attention initiation are a key marker of ASD, with children showing significantly fewer nonverbal behaviors to initiate shared experiences and marked differences in frequency of requesting behaviors 1, 2
Qualitatively impaired eye contact is a characteristic of ASD, with less frequent and poorly modulated eye contact, not simply reduced due to distractibility as in ADHD 1, 2

Children with ASD at 24 months demonstrate lower positive affect and higher negative affect compared to non-ASD siblings, indicating difficulties with emotional regulation 1, 2
Children with ASD show difficulty controlling behavior with lower sensitivity to social reward cues, highlighting challenges with behavioral regulation 1, 2
Poor effortful emotion regulation is a characteristic of ASD, which is qualitatively different from ADHD impulsivity 1, 2

ASD repetitive behaviors, such as hand flapping, finger flicking, rocking, spinning, and atypical movements, serve self-regulatory functions and are ego-syntonic, often increasing with stress or excitement 3
ADHD repetitive behaviors, such as fidgeting, difficulty remaining seated, and excessive talking, are driven by impulsivity and hyperactivity rather than self-regulation 4, 5, 6

The American Academy of Pediatrics recommends using standardized tools, such as ADOS and ADI-R, for direct observation of social-communication behaviors and developmental history, respectively, to assess core social-communication skills 1, 2
The M-CHAT is recommended for screening at 24 months to identify potential ASD cases 1

The American Academy of Pediatrics recommends screening for ADHD symptoms in every child with ASD, as inattention, impulsivity, and hyperactivity are among the most frequent associated symptoms 7, 8
Screening for ASD features in children presenting with ADHD who have prominent social difficulties is also recommended 7, 8

Both ASD and ADHD require screening for anxiety and depression, which are increased risks in both conditions, especially in adolescents 7, 8
Screening for learning disabilities, language disorders, sleep disorders, oppositional defiant disorder, conduct disorders, and tic disorders is also necessary, as these conditions can coexist with ASD and ADHD 7, 8, 3

The American Academy of Child and Adolescent Psychiatry recommends identifying joint attention deficits, such as failure to point to share interest, as a key differentiator between ASD and ADHD in children at 20 and 42 months 9
Children with ASD demonstrate qualitatively different social deficits, including impaired conventional gesture use, such as waving, nodding, and shaking head, which is preserved in ADHD 9
The use of others' bodies as tools, such as moving a parent's hand to open a door, is characteristic of ASD but not ADHD 9

The American Academy of Pediatrics recommends establishing a developmental timeline, including symptom onset before age 12, presence across multiple settings, and persistence regardless of sleep quality or other factors for ADHD diagnosis 10, 11
Obtaining information from at least two sources, such as parents and teachers, is crucial for documenting symptoms in more than one major setting for both ASD and ADHD diagnosis 10, 11

The American Academy of Pediatrics suggests screening for both ASD and ADHD simultaneously, as they frequently co-occur, and screening for anxiety and depression, which are increased risks in both conditions 10, 11

Screening for learning disabilities, language disorders, sleep disorders, oppositional defiant disorder, conduct disorders, and tic disorders is necessary for both ASD and ADHD diagnosis 10, 11

The Journal of the American Academy of Child and Adolescent Psychiatry warns against diagnostic overshadowing, where comorbid conditions are missed due to a more noticeable condition being present, and recognizes that anxiety symptoms can overlap between ASD and anxiety disorders 9