Dual board-certified Child, Adolescent, and Adult Psychiatrist Petaluma, California
Disclosure
The author reports no financial relationships with any companies whose products are mentioned in this article, or with manufacturers of competing products.
The differential diagnosis of ASD warrants careful attention and consideration to rule out other developmental and psychiatric conditions.
Intellectual disability (ID). DSM-5 diagnostic criteria for ASD necessitate that disturbances are not better explained by ID or global developmental delay and that deficits should exceed impairment consistent with the level of intellectual disability.28 Still, ASD is often overdiagnosed in children with ID.28 Research suggests phenotypic and genetic overlap between ID and ASD.28 Social functioning is often impaired in patients with ID; the greater the severity of ID, the greater the degree of social deficits.28 In approximately 30% of cases, ASD and ID are comorbid.6 This overlap and comorbidity can pose a challenge, particularly due to the inherent complexities involved in assessment and differentiation.28 When ID is present in ASD, there is a greater degree of social-communication deficits.6 It may be difficult to assess for ASD symptoms in children with severe ID.28 Although there is no minimum age or developmental level below which ASD should not be diagnosed, some studies have started to use minimum criteria for diagnosis, such as a nonverbal mental age of 18 months.28,40 Commonly used tests for ASD have much lower specificity when used for children with nonverbal age <15 months.28 It would make sense, then, that the presence of ID might significantly affect the results of these diagnostic tests.28
Other conditionsthat need to be ruled out include language disorders, hearing loss, rare genetic neurodevelopmental disorders (eg, Fragile X syndrome,3 Rett syndrome6), childhood-onset schizophrenia, obsessive-compulsive disorder, attachment disorders, and other conditions.18 ASD may be overdiagnosed in children with genetic disorders such as Angelman syndrome.41 In a systematic review, Moss and Howlin42 recommended caution when evaluating ASD-like behavioral symptoms in children with genetic syndromes and severe ID. On the other hand, some research has observed that individuals with Fragile X syndrome may exhibit symptoms that meet criteria for ASD.6,43 McDuffie et al43 used the Autism Diagnostic Interview-Revised (ADI-R) to compare boys with Fragile X syndrome who also met criteria for ASD with boys with nonsyndromic ASD. Those in the former group had lesser impairment in social smiling, offering, showing, and nonverbal gestures, but had more complex mannerisms, compared with boys in the latter group.43
Milder manifestations of ASD may be more challenging to diagnose,1 particularly in children age <3 and those with above-average cognition.6 Generally, in the case of a patient with ASD, parents find that the child did not have a period of typical development, or unusual behaviors were evident early on.17
ASD can be comorbid with ADHD. The presence of ADHD may mask or delay the diagnosis of ASD in children.6 In children with both ASD and ADHD, studies have found greater reduction in social and adaptive functioning compared with children with ADHD alone.44
Table 26,10,15,17,31,43 highlights some of the features that can be used to distinguish ASD from other conditions.
