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Introduction
Autism spectrum disorder (ASD) has increased in prevalence over the past three decades, with current prevalence estimates of 1 in 54 (Maenner et al., 2020). ASD is a neurodevelopmental disorder with two core symptoms:
social communication deficits and
restricted, repetitive behaviors and/or interests (American Psychiatric Association [APA], 2013).
However, the diagnosis of ASD is made more complicated by the heterogeneity of symptom presentation and the presence of co-occurring behavioral challenges (e.g. overactivity, aggression, language delays; Baker and Blacher, 2019; Eisenhower et al., 2007; Totsika et al., 2011). For example, many children with ASD also display symptoms similar to those observed in children with other neurodevelopmental disorders (e.g. attention-deficit hyperactivity disorder [ADHD] and intellectual disability [ID]).
The differential diagnosis of ASD has historically been difficult, with clinicians and researchers struggling to understand characteristics that are unique to ASD compared to other neurodevelopmental disorders. The diagnostic statistical manual of mental disorders, fifth edition (DSM-5; APA, 2013) provides clinicians with a framework to better understand the symptomatology of ASD and how to differentiate between various neurodevelopmental disorders. The most recent edition of the DSM (i.e. DSM-5) provided the umbrella term “autism spectrum disorder” (ASD), whereas DSM-IV and DSM-IV-TR had multiple diagnoses under this umbrella (American Psychiatric Association, 2000). Specifically, DSM-IV included diagnoses of autistic disorder, Asperger’s disorder and pervasive developmental disorder not otherwise specified (PDD-NOS). The 2013 conceptualization of ASD as a single umbrella diagnosis with varying levels of severity and the corresponding terminology helps to ensure that all individuals on the autism spectrum have an appropriate diagnosis and consequently receive adequate services (APA, 2013; Mahjouri and Lord, 2012).
Additionally, the symptomatology of ASD often overlaps with other neurodevelopmental disorders, leading to diagnostic difficulties (e.g. differential diagnosis, co-occurring diagnoses). Diagnostic screeners are not well equipped to distinguish between neurodevelopmental disorders. For example, screeners report heightened levels of inattention and hyperactivity/impulsivity behaviors for those diagnosed with ASD, ID and/or ADHD (McClain et al., 2017; Rommelse et al., 2018). This finding emphasizes the need for trained professionals to conduct a comprehensive assessment(s), thus providing an accurate diagnosis. The differential diagnosis of ASD and other developmental disorders is made complex by two diagnostic phenomena: diagnostic overshadowing and diagnostic substitution. Diagnostic overshadowing refers to the inaccurate...