Autism, the prototypic pervasive developmental disorder, ischaracterized by lifelong marked impairment in reciprocal socialinteraction, communication, and a restricted range of activitiesand interests (Table 20-2). Approximately 20% of parents reportrelatively normal development until 1 or 2 years of age, followedby a steady or sudden decline. If no clinical manifestations ofthe disorder are present by 3 years of age, Rett syndrome orchildhood disintegrative disorder need to be considered. As aninfant, there is delayed or absent social smiling. The young childmay spend hours in solitary play and be socially withdrawnwith indifference to attempts at communication. Patients withautism often are not able to understand nonverbal communication (eye contact, facial expressions) and do not interact withpeople as significantly different from objects. Speech often isdelayed and, when present, it is frequently dominated by echolalia (sometimes mistaken as a sign of obsessive-compulsivedisorder [OCD]), perseveration (confused with psychosis or
Table 20-1 Pervasive Developmental Disorder: Characteristics FEATURE AUTISM ASPERGER RETT CDD PDD-NOS Epidemiology 10 cases per 10,000; 5:1 male-to-female ratio 2.5 per 10,000; 5:1 male-to-female ratio 0.44 to 2.1 per 10,000; diagnosed only in girls; associated with MECP2 gene mutation 0.11 per 10,000 2 to 16 per 10,000
CDD, Childhood disintegrative disorder; PDD-NOS, pervasive developmental disorder-not otherwise specified.
OCD), pronoun reversal, nonsense rhyming, and other abnormalities. Intense absorbing interests, ritualistic behavior, andcompulsive routines are characteristic, and their disruptionoften invokes tantrum or rage reactions. Head banging, teethgrinding, rocking, diminished responsiveness to pain and external stimuli, and self-mutilation may be noted.
Although the etiology of autistic disorder is unknown, there is an increased risk of autistic disorder in siblings compared to the general population. Twin studies have revealed high levels of concordance for monozygotic twins. Family studies reveal prevalence rates of between 2% and 10% in siblings, and, when absent, there may be increased risk for language, learning, and social development problems.
It is proposed that the brain connectivity is adversely affected. Abnormalities in the limbic system, temporal, and frontal lobes have been suggested. Some postmortem studies reveal abnormalities in the brain microarchitecture, size, and neuronal packing. Functional magnetic resonance imaging (MRI) studies show hypoactivity of the fusiform gyrus of the amygdala, a location involved in face processing tasks and facial expression recognition involved in social and affective judgments.
The American Academy of Pediatrics recommends screening for autism at 18 and 24 months of age. Comprehensive testing should be done if there is an affected sibling or parental, other caregiver, or pediatric concern.
There are no definitive laboratory studies for autistic disorder, but they can help rule out other diagnoses. A hearing test (may account for the language deficits), chromosomal testing (to identify fragile X syndrome, tubular sclerosis, and genetic polymorphisms), congenital viral infections, and metabolic disorders (phenylketonuria) should be performed. Electroencephalography abnormalities may be seen in 20% to 25% of children with autism but are not diagnostic. Psychological tests in children with autism often show strengths in nonverbal tasks (e.g., puzzles) and marked deficiency in verbal cognitive abilities. IQ is usually low, though savant skills and hyperlexia (a precocious interest in letters and numbers) are sometimes observed. Speech pathology consultation can be helpful in evaluating the communication difficulties.