Pervasive Developmental Disorders
Pervasive developmental disorders include several disorders that are characterized by impaired reciprocal social interactions, aberrant language development, and restricted behavioral repertoire. Pervasive developmental disorders typically emerge in young children before the age of 3 years, and parents often become concerned about a child by 18 months as language development does not occur as expected. In about 25 percent of cases, some language develops and is subsequently lost. Some children with pervasive developmental disorders are not identified with problems until school age because they make relatively few demands and have minimal conflicts with others owing to their infrequent social engagement. Children with pervasive developmental disorders often exhibit idiosyncratic intense interest in a narrow range of activities, resist change, and are not appropriately responsive to the social environment. These disorders affect multiple areas of development, are manifested early in life, and cause persistent dysfunction.
The text revision of the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) includes five pervasive developmental disorders: autistic disorder, Rett’s disorder, childhood disintegrative disorder, Asperger’s disorder, and pervasive developmental disorder not otherwise specified. These are discussed in this chapter.
AUTISTIC DISORDER
Autistic disorder (historically called early infantile autism, childhood autism, or Kanner’s autism) is characterized by symptoms from each of the following three categories: qualitative impairment in social interaction, impairment in communication, and restricted repetitive and stereotyped patterns of behavior or interests.
In 1943 Leo Kanner, in his classic paper “Autistic Disturbances of Affective Contact,” coined the term infantile autism and provided a clear, comprehensive account of the early childhood syndrome. He described children who exhibited extreme autistic aloneness; failure to assume an anticipatory posture; delayed or deviant language development with echolalia and pronominal reversal (using you for I); monotonous repetitions of noises or verbal utterances; excellent rote memory; limited range of spontaneous activities, stereotypies, and mannerisms; anxiously obsessive desire for the maintenance of sameness and dread of change; poor eye contact; abnormal relationships with persons; and a preference for pictures and inanimate objects. Kanner suspected that the syndrome was more frequent than it seemed and suggested that some children with this disorder had been misclassified as mentally retarded or schizophrenic. Before 1980, children with pervasive developmental disorders were generally diagnosed with childhood schizophrenia. Over time, it became evident that autistic disorder and schizophrenia were two distinct psychiatric entities. In some cases, however, a child with autistic disorder may develop a comorbid schizophrenic disorder later in childhood.
Epidemiology
Prevalence.
Autistic disorder is believed to occur at a rate of about 8 cases per 10,000 children (0.08 percent). Multiple epidemiological surveys mainly in Europe have resulted in variable rates of autistic disorder ranging from 2 to 30 cases per 10,000. By definition, the onset of autistic disorder is before the age of 3 years, although in some cases, it is not recognized until a child is much older.
Some recent studies have shown an apparent increase in the prevalence of autistic disorder. One study reported a prevalence of 19.5 per 10,000 in California, which was also accompanied by a decreased prevalence of mental retardation. Other studies reported rates of up to 60 per 10,000 for autism. The evidence suggests that the majority, if not all, of the reported rise in incidence and prevalence is due to changes in diagnostic criteria; whether there has been a true increase in incidence is under investigation.
Sex Distribution.
Autistic disorder is four to five times more frequent in boys than in girls. Girls with autistic disorder are more likely to have more-severe mental retardation.
Socioeconomic Status.
Early studies suggested that a high socioeconomic status was more common in families with autistic children; however, these findings were probably based on referral bias. Over the last 25 years, no epidemiological studies have demonstrated an association between autistic disorder and any socioeconomic status.
Etiology and Pathogenesis
Genetic Factors.
Evidence supports a genetic basis for the development of autistic disorder in most cases, with a contribution of up to four or five genes. Family studies have demonstrated a 50 to 200 times increase in the rate of autism in siblings of an index child with autistic disorder. In addition, even when not affected with autism, siblings are at increased risk for a variety of developmental disorders often related to communication and social skills. These difficulties in the nonautistic relatives of persons with autistic disorder are also known by researchers as the “broad phenotype.” The specific modes of inheritance are not clear. Hypotheses include genetic inheritance of a more general predisposition to developmental difficulties and specific genetic etiology of autistic disorder.
The concordance rate of autistic disorder in the two largest twin studies was 36 percent in monozygotic pairs versus 0 percent in dizygotic pairs in one study and about 96 percent in monozygotic pairs versus about 27 percent in dizygotic pairs in the second study. High rates of cognitive difficulties, even in the nonautistic twin in monozygotic twins with perinatal complications, suggest that contributions of perinatal insult along with genetic vulnerability may lead to autistic disorder.
Fragile X syndrome, a genetic disorder in which a portion of the X chromosome fractures, appears to be associated with autistic disorder. Approximately 1 percent of children with autistic disorder also have fragile X syndrome. Children with fragile X syndrome tend to show gross motor and fine motor difficulties as well as relatively poorer expressive language compared with children with autism without fragile X syndrome. Tuberous sclerosis, a genetic disorder characterized by multiple benign tumors with autosomal dominant transmission, is found with greater frequency among children with autistic disorder. Up to 2 percent of children with autistic disorder may also have tuberous sclerosis.
Biological Factors.
The high rate of mental retardation among children with autistic disorder and the higher-than-expected rates of seizure disorders further support the biological basis for autistic disorder. Approximately 70 percent of children with autistic disorder have mental retardation. About one third of these children have mild to moderate mental retardation, and close to half of these children have severe or profound mental retardation. Children with autistic disorder and mental retardation typically show more-marked deficits in abstract reasoning, social understanding, and verbal tasks than in performance tasks, such as block design and digit recall, in which details can be remembered without reference to the “gestalt” meaning.
Of persons with autism, 4 to 32 percent have grand mal seizures at some time, and about 20 to 25 percent show ventricular enlargement on computed tomography (CT) scans. Various electroencephalogram (EEG) abnormalities are found in 10 to 83 percent of autistic children, and although no EEG finding is specific to autistic disorder, there is some indication of failed cerebral lateralization. Recently, one magnetic resonance imaging (MRI) study revealed hypoplasia of cerebellar vermal lobules VI and VII, and another MRI study revealed cortical abnormalities, particularly polymicrogyria, in some autistic patients. Those abnormalities may reflect abnormal cell migrations in the first 6 months of gestation. An autopsy study revealed fewer Purkinje’s cells, and another study found increased diffuse cortical metabolism during positron emission tomography scanning.
Autistic disorder is also associated with neurological conditions, notably congenital rubella, phenylketonuria, and tuberous sclerosis. Autistic children have higher-than-expected histories of perinatal complications compared with the general population and also compared with children with other psychiatric disorders. The finding that autistic children have significantly more minor congenital physical anomalies than expected suggests abnormal development within the first trimester of pregnancy.
Immunological Factors.
Several reports have suggested that immunological incompatibility (i.e., maternal antibodies directed at the fetus) may contribute to autistic disorder. The lymphocytes of some autistic children react with maternal antibodies, which raises the possibility that embryonic neural or extraembryonic tissues may be damaged during gestation. There is no proof that vaccination of children causes autistic disorder.
Perinatal Factors.
A higher-than-expected incidence of perinatal complications seems to occur in infants who are later diagnosed with autistic disorder. Maternal bleeding after the first trimester and meconium in the amniotic fluid have been reported in the histories of autistic children more often than in the general population. In the neonatal period, autistic children have a high incidence of respiratory distress syndrome and neonatal anemia. Males with autism, as a group, have been found to be the products of longer gestational age and were heavier at birth than babies in the general population. Females with autism are more likely to be the product of postterm pregnancies than babies in the general population.
Neuroanatomical Factors.
The neuroanatomical basis of autism is unknown; however, recent evidence suggests that enlargement of gray and white matter cerebral volumes, but not cerebellar volumes, are present in children with autistic disorder at 2 years of age. Head circumference appears normal at birth, and the increased rate of head circumference growth appears to emerge at about 12 months of age.
The temporal lobe is believed to be one of the critical areas of brain abnormality in autistic disorder. This suggestion is based on reports of autistic-like syndromes in some persons with temporal lobe damage. When the temporal region of animals is damaged, normal social behavior is lost, and restlessness, repetitive motor behavior, and a limited behavioral repertoire are seen. Some brains of autistic individuals exhibit a decrease in cerebellar Purkinje cells, which is believed to account potentially for abnormalities of attention, arousal, and sensory processes.
Biochemical Factors.
A number of studies in the last few decades have demonstrated that about one third of patients with autistic disorder have high plasma serotonin concentrations. This finding, however, is not specific to autistic disorder, and persons with mental retardation without autistic disorder also display this trait. Several studies have reported that autistic individuals without mental retardation have a high incidence of hyperserotonemia. In some autistic children, a high concentration of homovanillic acid (the major dopamine metabolite) in cerebrospinal fluid (CSF) is associated with increased withdrawal and stereotypes. Some evidence indicates that symptom severity decreases as the ratio of 5-hydroxyindoleacetic acid (5-HIAA, metabolite of serotonin) to homovanillic acid in CSF increases. The 5-HIAA concentration in CSF may be inversely proportional to blood serotonin concentrations, which are increased in one third of autistic disorder patients, a nonspecific finding that also occurs in persons with mental retardation.
Psychosocial and Family Factors.
Studies comparing parents of autistic children with parents of normal children have shown no significant differences in child-rearing skills.
Children with autistic disorder, as children with other disorders, can respond with exacerbated symptoms to psychosocial stressors, including family discord, the birth of a new sibling, or a family move. Some children with autistic disorder may be excruciatingly sensitive to even small changes in their families and immediate environment.
Diagnosis and Clinical Features
The DSM-IV-TR diagnostic criteria for autistic disorder are given in Table 38-1.
Physical Characteristics.
On first glance, children with autistic disorder do not show any physical signs indicating the disorder. These children do have high rates of minor physical anomalies, such as ear malformations and others that may reflect abnormalities in fetal development of those organs along with parts of the brain.
A greater-than-expected number of autistic children do not show lateralization and remain ambidextrous at an age when cerebral dominance is established in most children. Autistic children also have a higher incidence of abnormal dermatoglyphics (e.g., fingerprints) than those in the general population. This finding may suggest a disturbance in neuroectodermal development.
Table 38-1 DSM-IV-TR Diagnostic Criteria for Autistic Disorder | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Behavioral Characteristics
QUALITATIVE IMPAIRMENTS IN SOCIAL INTERACTION.
Autistic children do not exhibit the expected level of subtle reciprocal social skills that demonstrate relatedness to parents and peers. As infants, many lack a social smile and anticipatory posture for being picked up as an adult approaches. Less frequent or poor eye contact is common. The social development of autistic children is characterized by impaired, but not usually totally absent, attachment behavior. Autistic children often do not acknowledge or differentiate the most important persons in their lives—parents, siblings, and teachers—and may show extreme anxiety when their usual routine is disrupted, but they may not react overtly to being left with a stranger. When autistic children have reached school age, their withdrawal may have diminished and be less obvious, particularly in higher-functioning children. A notable deficit is seen in ability to play with peers and to make friends; their social behavior is awkward and may be inappropriate. Cognitively, children with autistic disorder are more skilled in visual-spatial tasks than in tasks requiring skill in verbal reasoning.
One description of the cognitive style of children with autism is that they cannot infer the feelings or mental state of others around them. That is, they cannot make attributions about the motivation or intentions of others and, thus, cannot develop empathy. This lack of a “theory of mind” leaves them unable to interpret the social behavior of others and leads to a lack of social reciprocation.
In late adolescence, autistic persons often desire friendships, but their difficulties in responding to another’s interests, emotions, and feelings are major obstacles in developing them. They are often shunned by peers and behave in awkward ways that alienate them from others. Autistic adolescents and adults experience sexual feelings, but their lack of social competence and skills prevents many of them from developing sexual relationships.
DISTURBANCES OF COMMUNICATION AND LANGUAGE.
Deficits in language development and difficulty using language to communicate ideas are among the principal criteria for diagnosing autistic disorder. Autistic children are not simply reluctant to speak, and their speech abnormalities do not result from lack of motivation. Language deviance, as much as language delay, is characteristic of autistic disorder. In contrast to normal children or those with mental retardation, autistic children have significant difficulty putting meaningful sentences together even when they have large vocabularies. When children with autistic disorder do learn to converse fluently, their conversations may impart information without providing a sense of acknowledging how the other person is responding. In children with autism and nonautistic children with language disorders, nonverbal communication skills may also be impaired when significant difficulty with expressive language exists.
In the first year of life, an autistic child’s pattern of babbling may be minimal or abnormal. Some children emit noises—clicks, sounds, screeches, and nonsense syllables—in a stereotyped fashion, without a seeming intent of communication. Unlike normal young children, who generally have better receptive language skills than expressive ones,
verbal autistic children may say more than they understand. Words and even entire sentences may drop in and out of a child’s vocabulary. It is not atypical for a child with autistic disorder to use a word once and then not use it again for a week, a month, or years. Children with autistic disorder typically exhibit speech that contains echolalia, both immediate and delayed, or stereotyped phrases that seem out of context. These language patterns are frequently associated with pronoun reversals. A child with autistic disorder might say, “You want the toy” when she means that she wants it. Difficulties in articulation are also common. Many children with autistic disorder use peculiar voice quality and rhythm. About 50 percent of autistic children never develop useful speech. Some of the brightest children show a particular fascination with letters and numbers. Children with autistic disorder sometimes excel in certain tasks or have special abilities; for example, a child may learn to read fluently at preschool age (hyperlexia), often astonishingly well. Very young autistic children who can read many words, however, have little comprehension of the words read.
verbal autistic children may say more than they understand. Words and even entire sentences may drop in and out of a child’s vocabulary. It is not atypical for a child with autistic disorder to use a word once and then not use it again for a week, a month, or years. Children with autistic disorder typically exhibit speech that contains echolalia, both immediate and delayed, or stereotyped phrases that seem out of context. These language patterns are frequently associated with pronoun reversals. A child with autistic disorder might say, “You want the toy” when she means that she wants it. Difficulties in articulation are also common. Many children with autistic disorder use peculiar voice quality and rhythm. About 50 percent of autistic children never develop useful speech. Some of the brightest children show a particular fascination with letters and numbers. Children with autistic disorder sometimes excel in certain tasks or have special abilities; for example, a child may learn to read fluently at preschool age (hyperlexia), often astonishingly well. Very young autistic children who can read many words, however, have little comprehension of the words read.
STEREOTYPED BEHAVIOR.
In the first years of an autistic child’s life, much of the expected spontaneous exploratory play is absent. Toys and objects are often manipulated in a ritualistic manner, with few symbolic features. Autistic children generally do not show imitative play or use abstract pantomime. The activities and play of these children are often rigid, repetitive, and monotonous. Ritualistic and compulsive phenomena are common in early and middle childhood. Children often spin, bang, and line up objects and may exhibit an attachment to a particular inanimate object. Many autistic children, especially those with severe mental retardation, exhibit movement abnormalities. Stereotypies, mannerisms, and grimacing are most frequent when a child is left alone and may decrease in a structured situation. Autistic children are generally resistant to transition and change. Moving to a new house, seeing that furniture in a room has been moved, or encountering a change, such as having breakfast before a bath when the reverse was the routine, may evoke panic, fear, or temper tantrums.
INSTABILITY OF MOOD AND AFFECT.
Some children with autistic disorder exhibit sudden mood changes, with bursts of laughing or crying without an obvious reason. It is difficult to learn more about these episodes if the child cannot express the thoughts related to the affect.
RESPONSE TO SENSORY STIMULI.
Autistic children have been observed to overrespond to some stimuli and underrespond to other sensory stimuli (e.g., to sound and pain). It is not uncommon for a child with autistic disorder to appear deaf, at times showing little response to a normal speaking voice; on the other hand, the same child may show intent interest in the sound of a wristwatch. Some children with autistic disorder have a heightened pain threshold or an altered response to pain. Indeed, some autistic children do not respond to an injury by crying or seeking comfort. Many autistic children reportedly enjoy music. They frequently hum a tune or sing a song or commercial jingle before saying words or using speech. Some particularly enjoy vestibular stimulation—spinning, swinging, and up-and-down movements.
ASSOCIATED BEHAVIORAL SYMPTOMS.
Hyperkinesis is a common behavior problem in young autistic children. Hypokinesis is less frequent; when present, it often alternates with hyperactivity. Aggression and temper tantrums are observed, often prompted by change or demands. Self-injurious behavior includes head banging, biting, scratching, and hair pulling. Short attention span, poor ability to focus on a task, insomnia, feeding and eating problems, and enuresis are also common among children with autism.
ASSOCIATED PHYSICAL ILLNESS.
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