When considering the diagnosis of ASD, physicians refer to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)1 to determine whether or not a child meets the criteria-based diagnosis for a disorder within the spectrum. The definition and criteria for ASD have been broadened to include milder forms. The newest criteria (Table 1 in the accompanying technical report 2) can be found in the DSM-IV1 or the DSM for Primary Care, Child and Adolescent Version 50 published by the Academy. These criteria were established for children 3 years and older and may be difficult to apply to younger children. If a child meets some but not all criteria, the diagnosis of PDD-NOS may apply.
Alternative tools have been developed to aid physicians in screening for ASD in younger children. These relatively new instruments, although promising, need additional validation to assess their sensitivity and specificity across various ethnic populations. The Checklist for Autism in Toddlers (CHAT; Fig 1 in accompanying technical report 2) was developed in England for use with 18-month-old children and has been used to screen more than 16 000 toddlers. 51-53 Although it has a high specificity, its relatively low sensitivity is a concern. A modified version of the CHAT is being developed to address this issue. The Pervasive Developmental Disorder Screening Test is a parent-completed survey of early signs and symptoms of ASD, but less is known about its sensitivity and specificity. 54 When ASD is suspected on the basis of clinical symptoms or results of these or similar screening tools, a comprehensive assessment (including autism-specific tools 2-4,36) should be performed by a specialist or, preferably, a multidisciplinary team of specialists with expertise in ASD to make the definitive diagnosis and search for possible etiologic disorders.
Most children with idiopathic ASD have a normal physical appearance except for the presence of macrocephaly in 25%. 55,56 Thus, the physical examination, including a detailed neurologic examination, may be more helpful in determining the presence or absence of an associated medical condition. A recognizable etiologic disorder occurs in less than 25% of cases of ASD. 57 Although now rare because of widespread immunization, congenital rubella is associated with autistic behaviors, severe mental retardation, microcephaly, congenital heart defects, and vision and hearing impairments. 31,32 Dysmorphic characteristics of more common etiologic conditions include the long face, large ears, and large testes (postpubertally) associated with fragile X syndrome; the hypopigmented ash leaf macules, facial angiofibromas, and seizures associated with tuberous sclerosis; and the ataxic gait and broad mouth with persistent large smile associated with Angelman syndrome.
In addition to making the clinical diagnosis of ASD, the pediatrician is faced with deciding which diagnostic tests are indicated to determine the cause of ASD, determine whether there are comorbid disorders, and rule out disorders included in the differential diagnosis. Some measure of the child's overall level of cognitive functioning and adaptive skills is necessary, especially if there is a concern about comorbid mental retardation. An audiologic evaluation and a comprehensive speech and language evaluation should be done in any child who has language delays whether or not autistic features are present. Other tests to consider include a lead screening, amino acid screening to detect phenylketonuria, DNA analysis to detect fragile X syndrome, high-resolution chromosome analysis, and prolonged sleep-deprived electroencephalography (in children who have symptoms of developmental regression or clinical seizures or when there is a high suspicion of subclinical seizures).3,4 Computed tomography or magnetic resonance imaging is not routinely indicated and probably will not be helpful in the child with ASD who has isolated macrocephaly and no localizing signs. 3,4,58,59 The need for diagnostic studies must be evaluated on the basis of specific signs in the individual child and the possible contribution the results will make to genetic counseling and management rather than using a "shotgun" approach.
To summarize diagnostic challenges facing the pediatrician, there must be a high index of suspicion, especially when parents have concerns about their child's language and social development, and extra attention should be given to subsequent siblings of children with isolated ASD. Pediatricians with adequate training and experience are encouraged to use autism-specific diagnostic tools to make the definitive diagnosis and additional diagnostic tools to search for an etiologic or comorbid disorder. The importance of early diagnosis cannot be overemphasized. If a primary care physician is uncomfortable with making the diagnosis, the child should be promptly referred to a specialist or, preferably, a team of specialists with expertise in the diagnosis of ASD. Primary care physicians seeking assistance with an etiologic diagnosis may additionally request a genetics consultation.
