Diagnosis, Assessment, and Prevalence
The diagnosis of autism and related autistic spectrum disorders in young children is often relatively straightforward but can, at times, be challenging (Lord, 1997). Complexities in diagnosis and evaluation relate to the range of syndrome expression in these conditions along various dimensions such as language abilities and associated mental handicap (Volkmar et al., 1997); differential diagnosis, particularly in children younger than 3 years (Lord and Schopler, 1989); concerns regarding labeling (Hobbs, 1975) and diagnostic terminology within school systems; and lack of expertise in assessment and diagnosis among some educational professionals (Siegel et al., 1988).
In general, the perspectives of various professionals are required as part of the diagnostic process. This may involve the efforts of special educators, general educators, psychologists, speech pathologists, occupational and physical therapists, and physicians. The need for a multidisciplinary or transdisciplinary perspective can create challenges for local educational authorities. Although the mandate of the local education authority (LEA) and state-funded developmental disability programs is to provide appropriate education, the services of non-LEA specialists are required for initial identification, diagnosis, and clinical services related to the presence of additional handicapping conditions. A LEA and state services may need to form relationships with individuals and centers with such expertise. Although various rating scales and checklists have been developed to aid in the process of assessment, these do not replace
the need for a thoughtful and comprehensive diagnostic assessment (discussed below)—this is particularly true for preschool children, for whom issues of diagnosis can be complicated.
PREVALENCE OF AUTISM AND RELATED CONDITIONS
Epidemiological studies of autism have important implications for both research and clinical service, for example, through helping to plan for the need for special services and selecting samples for research studies. Fombonne (1999) has recently summarized the available research on this topic and systematically reviewed more than 20 studies conducted in ten countries. As he notes, although important details were sometimes lacking in the studies, the total population base included in the review was approximately 4 million children surveyed.
Studies have typically employed a two-stage design, with an initial screening followed by more systematic assessment. Complexities in interpreting the available data include variations in approaches to diagnosis of autism and differences in screening methods. In the studies surveyed, approximately 80 percent of individuals with autism also exhibited mental handicap (i.e., mental retardation). Studies have also consistently identified more boys with autism than girls (three to four boys for every girl). In addition, girls with autism are more likely than boys to also exhibit mental handicaps.
The epidemiology of autism has recently become quite controversial. In the United States, increased demand for autism-specific services (Fombonne, 1999) has drawn attention to growing numbers of children with the educational categorization of autism. Large, systematic epidemiologic studies have reported increases in prevalence from the estimated rate of 2–5 per 10,000 in the 1970s to 6–9 per 10,000. Fombonne (1999) considers a rate of 7.5 per 10,000 to best reflect the result of studies conducted since 1987. Those studies also report a rate of 12.5 per 10,000 individuals for atypical autism/pervasive developmental disorders, producing an overall rate of about 20 cases per 10,000. Rates for Asperger’s disorder, excluding individuals who also met criteria for autism, were low, at 1–2 per 10,000. Because the studies did not consider individuals with less-pronounced variants of autistic spectrum disorder, it is possible that the figures for atypical autism/pervasive developmental disorder and Asperger’s disorder are underestimates.
Two simple reasons explain the difference in current and historical rates: more complete diagnoses and a broader definition of autistic spectrum disorders (Fombonne, 1999). However, there are a number of recent studies, most with small samples, and several reports from school systems that found even higher rates of autism (Centers for Disease Control and Prevention, 2000; Arvidsson et al., 1997; Baird et al., 2000; Kadesjoe et
al., 1999; California Department of Developmental Services, 2000). Studies reporting much higher rates were from relatively small samples or from state surveys, in which an educational label of autism was associated with provision of intensive services and thus highlight the need for further, well-designed investigations. For example, the Department of Education’s Office of Special Education Programs (OSEP) could support a research study examining the prevalence and incidence of autism, using OSEP data gathered for school-age children since the autism category was recognized in 1991. This study could investigate in particular whether the dramatic increases in numbers of children served with autistic spectrum disorders are offset by commensurate decreases in categories in which children with autism might have previously been misclassified.
The symptoms of autism are often measurable by 18 months of age (Charman et al., 1997; Cox et al., 1999; Lord, 1995; Stone et al., 1999; Baird et al., 2000). The main characteristics that differentiate autism from other developmental disorders in the 20-month to 36-month age range involve behavioral deficits in eye contact, orienting to one’s name, joint attention behaviors (e.g., pointing, showing), pretend play, imitation, nonverbal communication, and language development (Charman et al., 1997; Cox et al., 1999; Lord, 1995; Stone et al., 1999). There are three published screening instruments in the field that focus on children with autism: the Checklist for Autism in Toddlers (Baird et al., 2000), the Autism Screening Questionnaire (Berument et al., 1999), and the Screening Test for Autism in Two Year Olds (Stone et al., 2000).
The Checklist for Autism in Toddlers (CHAT) (Baron-Cohen et al., 1992; 1996) is designed to screen for autism only at 18 months of age. From both the initial study of siblings of children with autistic disorder and from a larger epidemiological study involving a population study of 16,000 18-month-old infants (excluding children with suspected developmental delays), virtually all the children failing the five item criterion on the CHAT administered twice (one month apart, the second time by an experienced clinician and including other sources of information) were found to have autistic disorder when diagnosed at 20 and 42 months (Baron-Cohen et al., 1992; Baron-Cohen et al., 1996; Charman et al., 1998; Cox et al., 1999). However, the CHAT was less sensitive to milder symptoms of autism; children later diagnosed with other autistic spectrum disorders did not routinely fail the CHAT at 18 months. Follow-up of the cases at age 7 revealed that this instrument had a high specificity (98%) but relatively low sensitivity (38%) (Baird et al., 2000), suggesting that it is not appropriate for screening.
The Autism Screening Questionnaire is a new 40-item screening scale
that has good discriminative validity between autistic spectrum and other disorders, including nonautistic mild or moderate mental retardation, in children age 4 years and older; it has not yet been tested with very young children. A score of 1 is given for an item if the abnormal behavior is present and a score of 0 if the behavior is absent. The cutoff for consideration of a diagnosis of autism is a score of 15 or higher. Further reliability studies and validation studies in younger children are ongoing. The recently published Screening Test for Autism in Two-Year Olds (Stone et al., 2000) is a direct observational scale; it showed good discrimination between children with autism and other developmental disorders in a small sample of two-year-old children.
Several additional instruments are currently undergoing validation studies. The Australian Scale for Asperger’s Syndrome (Garnett and Attwood, 1998) is a parent or teacher rating scale for high-functioning older children on the autistic spectrum who remain undetected at schoolage. The Pervasive Developmental Disorders Screening Test-II (PDDST-II) is a clinically derived parent questionnaire designed in three formats: Stage 1 is aimed for use in the primary care setting, Stage 2 for use in developmental clinics, and Stage 3 for use in autism clinics. The Modified Checklist for Autism in Toddlers (M-CHAT) expands the CHAT into a 23-item checklist that a parent can fill out in about 10 minutes (Robins et al., 1999). Other approaches are being developed.
Developmentally based assessments of cognitive, communicative, and other skills provide information important for both diagnosis and program planning for children with autism and related conditions. Careful documentation of a child’s unique strengths and weaknesses can have a major impact on the design of effective intervention programs and is particularly critical, because unusual developmental profiles are common. Given the multiple areas of difficulty, the efforts of professionals from various disciplines are often needed (e.g., psychology, speech and language pathology, neurology, pediatrics, psychiatry, audiology, physical and occupational therapy). The level of expertise required for effective diagnosis and assessment may require the services of individuals, or a team of individuals, other than those usually available in a school setting (Sparrow, 1997). In some cases, psychological and communication assessments can be performed by existing school staff, depending on their training and competence in working with children with autism. However, other services (e.g., genetic testing, drug therapy, management of seizures) are necessarily managed in the health care sector. Some children may fall between systems and therefore not be served well.
Several principles underlie assessment of a young child with autism
or autistic spectrum disorder (Sparrow, 1997):
Multiple areas of functioning must typically be assessed, including current intellectual and communicative skills, behavioral presentation, and functional adjustment.
A developmental perspective is critical. Given the strong association of mental retardation with autism, it is important to view results within the context of overall developmental level.
Variability of skills is typical, so it is important to identify a child’s specific profile of strengths and weaknesses rather than simply present an overall global score. Similarly, it is important not to generalize from an isolated or “splinter” skill to an overall impression of general level of ability, since such skills may grossly misrepresent a child’s more typical abilities.
Variability of behavior across settings is typical. Behavior of a child will vary depending on such aspects of the setting as novelty, degree of structure provided, and complexity of the environment; in this regard, observation of facilitating and detrimental environments is helpful.
Functional adjustment must be assessed. Results of specific assessments obtained in more highly structured situations must be viewed in the broader context of a child’s daily and more typical levels of functioning and response to real-life demands. The child’s adaptive behavior (i.e., capacities to translate skills into real world settings) is particularly important.
Social dysfunction is perhaps the most central defining feature of autism and related conditions, so it is critical that the effect of a child’s social disability on behavior be considered.
Behavioral difficulties also must be considered, since they affect both the child’s daily functioning and considerations for intervention.
Various diagnostic instruments can be used to help structure and quantify clinical observations. Information can be obtained through observation (e.g., the Autism Diagnostic Observation Scale, Lord et al., 2000) as well as the use of various diagnostic interviews and checklists, e.g., Autism Diagnostic Interview-Revised (Lord et al. 1994); Childhood Autism Rating Scale (Schopler et al., 1980); Autism Behavior Checklist (Krug et al., 1980); Aberrant Behavior Checklist (Aman and Singh, 1986). An adequate assessment will involve both direct observation and interviews of parents and teachers.
The range of syndrome expression in autism and autistic spectrum disorders is quite broad and spans the entire range of IQ (Volkmar et al., 1997). A diagnosis of autism or autistic spectrum disorder can be made in a child with severe or profound mental retardation as well as in a child
who is intellectually gifted. In addition, individuals vary along a number of other dimensions, such as levels of communicative ability and degree of behavioral difficulties. As a result, in working with a child with an autistic spectrum disorder, considerable expertise is required of the various evaluators. Evaluators must consider the quality of the information obtained (both in terms of reliability and validity), the involvement of parents and teachers, the need for interdisciplinary collaboration, and the implications of results for intervention. Coordination of services, including specialized assessment services, is important, as is facilitating discussion between members of assessment and treatment teams and parents (Filipek et al., 1999; Volkmar et al., 1999).
A range of components should be part of a comprehensive educational evaluation of young children with autism. These include obtaining a thorough developmental and health history, a psychological assessment, a communicative assessment, medical evaluation, and, in some cases, additional consultation regarding aspects of motor, neuropsychological, or other areas of functioning (Filipek et al., 1999; Volkmar et al., 1999). This information is important both to diagnosis and differential diagnosis and to the development of the individual educational intervention plan.
The psychological assessment should establish the overall level of cognitive functioning as well as delineate a child’s profiles of strengths and weaknesses (Sparrow, 1997). This profile should include consideration of a child’s ability to remember, solve problems, and develop concepts. Other areas of focus in the psychological assessment include adaptive functioning, motor and visual-motor skills, play, and social cognition. Children will usually need to be observed on several occasions during more and less structured periods.
The choice of assessment instruments is a complex one and depends on the child’s level of verbal abilities, the ability to respond to complex instructions and social expectations, the ability to work rapidly, and the ability to cope with transitions in test activities (the latter often being a source of great difficulty in autism). Children with autism often do best when assessed with tests that require less social engagement and less verbal mediation. In addition to the formal quantitative information provided, a comprehensive psychological assessment will also provide a considerable amount of important qualitative information (Sparrow, 1997). It is important that the psychologist be aware of the uses and limitations of standardized assessment procedures and the difficulties that children with autism often have in complying with verbal instructions and social reinforcement. Operant techniques may be helpful in facilitating assessment.
Difficulties in communication are a central feature of autism, and they interact in complex ways with social deficits and restricted patterns of behavior and interests in a given individual. Accurate assessment and
understanding of levels of communicative functioning is critical for effective program planning and intervention. Communication skills should be viewed in a broad context of an individual’s development (Lord and Paul, 1997; Prizant and Schuler, 1997); standardized tests constitute only one part of the assessment of communication abilities in younger children with autism and related conditions. The selection of appropriate assessment instruments, combined with a general understanding of autism, can provide important information for purposes of both diagnostic assessment and intervention.
In addition to assessing expressive language, it is very important to obtain an accurate assessment of language comprehension. The presence of oral-motor speech difficulties should be noted. In children with autism, the range of communicative intents may be restricted in multiple respects (Wetherby et al., 1989). Delayed and immediate echolalia are both common in autism (Fay, 1973; Prizant and Duchan, 1981) and may have important functions. In addition, various studies have documented unusual aspects even of very early communication development in autism (Ricks and Wing, 1975; Tager-Flusberg et al., 1990).
In assessing language and communication skills, parent interviews and checklists may be used, and specific assessment instruments for children with autistic spectrum disorders have been developed (Sparrow, 1997). For children under age 3, scores on standardized tests may be particularly affected by difficulties in assessment and by the need to rely on parent reports and checklists. For preverbal children, the speech-communication assessment should include observation of a child’s level of awareness of communication “bids” from others, the child’s sense of intentionality, the means used for attempting communication, and the quality and function of such means, sociability, and play behaviors. The evaluator should be particularly alert to the child’s capacity for symbolic behavior, because this has important implications for an intervention program (Sparrow, 1997). There are also several standardized instruments that provide useful information on the communication and language development of preverbal children with autism; these include the Communication and Symbolic Behavior Scales, the Mullen Scales of Early Learning, and the MacArthur Communicative Development Inventory. For children with some verbal ability, social and play behaviors are still important in terms of clinical observation but various standardized instruments are available as well, particularly when a child exhibits multiword utterances. Areas to be assessed include receptive and expressive vocabulary, expressive language and comprehension, syntax, semantic relations, morphology, pragmatics, articulation, and prosody.
The choice of specific instruments for language-communication assessment will depend on the developmental levels and chronological age of the child. For higher functioning individuals with autism or Asperger’s
syndrome, additional observations may address aspects of topic management and conversational ability, ability to deal with nonliteral language, and language flexibility. As with other aspects of assessment, an evaluator should be flexible and knowledgeable about the particular concerns related to assessment of children with autism.
Motor abilities in autism may, at least in the first years of life, represent an area of relative strength for a child, but as time goes on, the development of motor skills in both the gross and fine motor areas may be compromised, and motor problems are frequently seen in young children with autism. Evaluations by occupational and physical therapists are often needed to document areas of need and in the development of an intervention program (Jones and Prior, 1985; Hughes, 1996). Standardized tests of fine and gross motor development and a qualitative assessment of other aspects of sensory and motor development, performed by a professional in motor development, may be helpful in educational planning.
For very young children, there may be concerns about the child recognized or first expressed in the context of well-child care. The education of physicians, nurses, and others regarding warning signs for autistic spectrum disorders is very important. After initial referral for assessment and diagnosis, consultations with other medical professionals may be indicated, depending on the context (Filipek et al., 1999; Volkmar et al., 1999), for example, to developmental and behavioral pediatricians, child psychiatrists, geneticists, and pediatric neurologists. When this consultation is relevant to the educational program, reimbursement may appropriately be made by the local education authority.
The available literature has clearly documented that children with autism are at risk for developing seizure disorders throughout the developmental period (Deykin and MacMahon, 1979; Volkmar and Nelson, 1990). Seizure disorders in autism are of various types and may sometimes present in unusual ways. Although not routinely indicated, an electroencephalogram (EEG) and/or neurological consultation is indicated if any symptoms suggestive of seizures, such as staring spells, are present. The presence of a family history of developmental delay or unusual aspects of a child’s history or examination may suggest the need for genetic or other consultation. In some cases, autism may be associated with other conditions—notably fragile X syndrome and tuberous sclerosis (Dykens and Volkmar, 1997).
A child’s hearing should be tested, but behavioral problems may sometimes complicate assessment. Definitive documentation of adequate
hearing levels should then be obtained through other methods, such as auditory brainstem evoked responses (BSERs) (Klin, 1993). Certain features, such as the abrupt behavioral and developmental deterioration of a child who was previously developing normally, may suggest the importance of extensive medical investigations (Volkmar et al., 1999).
In some cases, the use of psychotropic medications may be indicated for young children (see Chapter 10). Although not curative, such medications may help to reduce levels of associated maladaptive behaviors and help children profit from educational programming. The use of such agents requires careful consideration of potential benefits and risks and the active involvement of parents and school staff (see Volkmar et al., 1999 for a review).
IMPLICATIONS FOR INTERVENTION
Many aspects of the procedures, curricula, and educational programs relevant to other children are readily applicable to children with autism and related conditions. As for all children, an intervention program must be individualized and tailored to the specific needs, strengths, and weaknesses of the individual child. In addition, children with autistic spectrum disorders often present special challenges for intervention.
From the time of Kanner’s (1943) definition of autism, social deficits have been consistently identified as an, if not the, essential feature of the condition. Social interaction requires careful attention to multiple, shifting strands of information; an ability to perceive the thoughts, feelings, and intentions of others; and coping with novel situations on a regular basis. In children with autistic spectrum disorders, social difficulties persist over time, although the nature of the social difficulties may change with age and intervention (Siegel et al., 1990). These social difficulties, as reflected in relationships with teachers and particularly in relationships with peers, are different from those seen in all other developmental disorders and present special difficulties for programming. For a child with an autistic spectrum disorder to be able to be included in mainstream settings, the child must be able to manage social experiences. This requires careful consideration on the part of school staff. While children with an autistic spectrum disorder can be served within many school environments, even for more cognitively able individuals this can be a challenge. The characteristic difficulties in social interaction require special teacher training and support beyond knowledge concerning general developmental delays or other learning disabilities.