Autism: A three-step practical approach to making the diagnosis

After the preliminary history and exam, you should have an initial impression as to whether a PDD may be present. Conditions that could mimic or co-exist with autism will then need to be evaluated (Table 2).

Hearing and vision testing Every child presenting with a language or cognitive delay should have an adequate hearing assessment, including an audiogram at the very least. If results are equivocal, then brainstem auditory-evoked responses are indicated to establish the auditory system’s integrity. Vision screening should be completed, and the child should be referred to an ophthalmologist if a problem is suspected.

IQ testing A child with cognitive delays, learning problems, or suspected PDD should be referred to an experienced psychologist for intelligence testing. Public school systems often provide this service. Intelligence testing can document mental retardation and offer important information about the child’s strengths and weaknesses in learning.

Speech and language assessment A speech and language pathologist should evaluate children with PDD and/or language problems for articulation, prosody, receptive and expressive language, and pragmatics.

Lab and genetic tests Laboratory investigation in a child with cognitive delays should include routine blood chemistries, CBC, thyroid function tests, and lead level. Screen for fragile X syndrome, as its symptoms overlap those of autism, and for disorders of amino acid and organic acid metabolism. Finally, consider a chromosome karyotype, especially in patients with dysmorphic features on physical exam.

Table 1

THE THREE DOMAINS OF IMPAIRMENT IN AUTISM

EEG Obtain a sleep-deprived electroencephalogram (EEG) in children with a history of significant language regression, episodic symptoms, or other indicators of possible seizures. Ideally, the EEG should include monitoring during sleep to help rule out acquired epileptic aphasia (Landau-Kleffner syndrome), a rare disorder associated with late-onset language regression. MRI of the brain is not routine but should be considered if indicated by the history or neurologic exam.

Consultations Consider consulting colleagues in neurology and medical genetics, especially when patients present with definite neurologic signs and symptoms or obvious dysmorphic features. These medical specialists are trained to screen for complex and rare syndromes that are sometimes associated with features of PDD.

Step 2. Is it PDD or another psychiatric disorder?

Psychiatric disorders that can be mistaken for PDD are listed in Table 3. The central feature of all PDDs is disturbance in social relatedness, and a diagnosis of PDD requires a history of significant social impairment.

Problems with social reciprocity in PDD are qualitatively different from the social impairment seen in other psychiatric disorders. For example, a child with attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) may have few friends because of a tendency to act impulsively and get into frequent conflicts with others. These social difficulties would not be considered indicative of PDD, as they typify those seen in children with ADHD and ODD.

Mental retardation Although mental retardation occurs in approximately 75% of persons with autism, most patients with mental retardation do not have autism. In assessing an individual with mental retardation for symptoms of PDD, consider the overall developmental level. It is not uncommon for individuals with mental retardation to have mild social problems, a history of language delay, and even motor stereotypies. These symptoms are considered indicative of PDD only when they are more severe than would be expected for the patient’s developmental level.

Table 2

TESTING OPTIONS FOR PATIENTS WITH PDD

Table 3