Identification and Diagnosis of Autism Spectrum Disorders: An Update

The Diagnostic and Statistical Manual of Mental Disorders 4th Edition (DSM-IV-TR)^[4] and 10th Revision of the International Classification of Diseases (ICD-10)^[5] criteria (for 'autistic disorder' and 'childhood autism', respectively) each contain definitions of difficulties under the three main areas of: communication; social interaction; and restricted, repetitive and stereotyped behaviors.

Specific difficulties relating to communication range from the total absence of speech (without the use of gestures to compensate) to the use of language that is excessively repetitive or unusually stereotyped. Speech may also be considered abnormal in terms of the quality of intonation, pitch and stress. Aspects of communication-related difficulties also include an inability to maintain a two-way conversation, as well as a lack of pretend play.

Social interaction difficulties include difficulties with nonverbal aspects of communication, such as the use of gestures, eye contact and facial expressions. Other specified difficulties with social interaction include problems making friends with other children, a lack of spontaneous showing and pointing by the child to share their interests with others, and a lack of emotional reciprocity, such as not responding to the changing emotions of other people.

Problems relating to restricted, repetitive and stereotyped behaviors include intense preoccupations and obsessions with specific objects or topics of interest, odd mannerisms such as hand-flapping and finger-flicking and an insistence on following fixed routines.

In addition, there is a requirement that at least one area of difficulty was present before 3 years of age. In all cases, the nature of the difficulty should be such that it causes a significant problem with everyday functioning.

The term pervasive developmental disorder – not otherwise specified (PDD-NOS) as defined in the DSM-IV-TR is used where there is evidence that the child has difficulties that are clearly related to the autism spectrum, but the full criteria for autistic disorder are not met. This generally means that the child does not have a clinically significant problem in one of the three main areas of autism, or that there was no evidence of onset of difficulties before 3 years of age. In DSM-IV-TR the term atypical autism is used more-or-less interchangeably with the term PDD-NOS. In ICD-10, atypical autism is defined more specifically in relation to either late-onset or atypical symptomatology or both.

As for autism, the DSM-IV-TR and ICD-10 definitions of Asperger syndrome (specifically termed 'Asperger's disorder' and 'Asperger's syndrome', respectively) differ in their precise detail, but overlap almost entirely in their broad focus. In relation to social interaction and restricted, repetitive and stereotyped behaviors, the criteria are virtually identical to those specified for autism. The nature of some of the behaviors may be more subtle than for those typical in autism, in that hand flapping and preoccupations with objects are less likely to occur. However, lining up toys in a repetitive or obsessive way, or an extremely intense interest in a particular topic, such as dinosaurs or trains, is more common.

One distinction from the criteria for autism is that for Asperger syndrome, the main milestones of speech development, defined as the use of single words by 2 years of age and the use of simple phrases by 3 years of age, should have been met. However, this does not mean that a person with Asperger syndrome uses their language in a functional, communicative and reciprocal way, and there are generally difficulties with the nonverbal aspects of communication (e.g. eye contact, gestures, facial expression and 'body language'). The criteria for Asperger syndrome also specify that there should be no delay in cognitive development. In general, this means that the child or adolescent should be within the average range or above in terms of intellectual ability. More specifically, this means that the person should have an IQ of at least 70. The descriptions of autism do not mention cognitive or intellectual ability as a defining criterion, meaning that individuals diagnosed with autism may have a learning disability – 'mental retardation' in the USA – defined as an IQ of less than 70, or that that IQ may be in the normal range or above.

Existing information from all settings should be gathered.

A specific autism spectrum disorder (ASD) developmental and family history should be taken. This history should be taken by an experienced team member with recognized ASD training. In some cases it may be useful to use a semistructured interview such as the Autism Diagnostic Interview – Revised^[17] or the Diagnostic Interview for Social and Communication Disorders.^[20] If the person taking the developmental history is not medically trained, then the medical history and examination should be completed separately.

Focused observations should be taken across more than one setting. This could include tools such as the Autism Diagnostic Observation Schedule.^[17] The focus of the assessment of primary school-aged children should include their functioning in an educational setting.

A cognitive assessment should be performed in an appropriate setting by either a clinical or an educational psychologist with ASD training.

A communication assessment should be made and speech and language competences assessed where needed by a speech and language therapist with ASD training.

An assessment should be made of mental health and behavior.

An assessment of the needs and strengths of all family members should be undertaken.

A full physical examination should be performed including appropriate medical tests. Choice of tests will depend on each child's clinical presentation but chromosome karyotype and fragile X DNA analysis are the only current routine recommendations. Clinical evidence of comorbid medical conditions such as epilepsy should be sought but tests such as EEG should not be undertaken unless clinically appropriate. The evidence base for all investigations should be fully explained to parents.

Other assessments may be required to investigate unusual sensory responses, motor planning and co-ordination difficulties and self-care problems.

In the years since Lotter's study,^[35] there have been a number of studies investigating the prevalence of autism. Wing and Gould conducted a study involving children defined as having special educational needs, which meant that virtually all of them had an IQ below 70.^[52] This study confirmed Lotter's reported prevalence of approximately 4–5 per 10,000 for children meeting the narrowest criteria for Kanner-type autism.^[35] However, there were about three-times as many who met a broader definition for autism, resulting in a combined prevalence of approximately 20 per 10,000 children. A later study carried out in Gothenberg, Sweden, included children with IQs of 70 and above.^[53] This study reported a prevalence for Asperger syndrome and 'high-functioning autism' of 36 per 10,000 children, with an additional 35 per 10,000 children identified as having social impairment but not meeting the full diagnostic criteria.

Combining the figures from these two studies suggests that the total prevalence for autism spectrum disorder is approximately 56 per 10,000 (i.e., 20 + 36). Taking the broadest definition from the Swedish study, which would probably include many individuals who would meet the criteria for pervasive developmental disorder – not otherwise specified and atypical autism, the total prevalence figure would be approximately 91 per 10,000 (i.e., 56 + 35), equivalent to a little under 1%.

This figure has been widely reported over the past few years, and to some extent has become the benchmark against which claims of a dramatic increase in the prevalence of autism can been measured. The Baird et al. study, estimating total prevalence as just over 1%, breaks down the overall figure, providing a basis for more specific comparison with earlier estimates.^[36] For the most narrowly defined group, who met the criteria for the 10th Revision of the International Classification of Diseases for childhood autism and the classifications for autism and/or autism spectrum on the Autism Diagnostic Interview – Revised and the Autism Diagnostic Observation Schedule, the prevalence was just below 25 per 10,000. When these criteria were expanded to allow for those for whom there was a consensus amongst expert diagnosticians that the child had autism, even if the results from the diagnostic instruments were not in complete agreement, the prevalence rose to just below 39 per 10,000. The proportion of children meeting the criteria for 'other autism spectrum disorder' (including pervasive developmental disorders/autism spectrum disorder) was 77 per 10,000 – hence the total figure of 116 per 10,000 (i.e., 39 + 77).