Several factors complicate the diagnosis of Asperger syndrome (AS), an autism spectrum disorder (ASD). Like other ASD forms, Asperger syndrome is characterized by impairment in social interaction accompanied by restricted and repetitive interests and behavior; it differs from the other ASDs by having no general delay in language or cognitive development. Problems in diagnosis include disagreement among diagnostic criteria, the controversy over the distinction between AS and other ASD forms or even whether AS exists as a separate syndrome, and over- and under-diagnosis for non-technical reasons. As with other ASD forms, early diagnosis is important, and differential diagnosis must consider several other conditions.
Criteria
Asperger syndrome is defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) as a pervasive developmental disorder that is distinguished by a pattern of symptoms rather than a single symptom. It is characterized by impairment in social interaction, by stereotyped and restricted patterns of behavior, activities and interests, and by no clinically significant delay in cognitive development or general delay in language. Impairments must be significant, and must affect important areas of function, and the diagnosis is excluded if criteria are also met for autism. Intense preoccupation with a narrow subject, one-sided verbosity, restricted prosody, and physical clumsiness are typical of the condition, but are not required for diagnosis.
The World Health Organization ICD-10 criteria are almost identical to DSM-IV: ICD-10 adds the statement that motor clumsiness is usual (although not necessarily a diagnostic feature); ICD-10 adds the statement that isolated special skills, often related to abnormal preoccupations, are common but are not required for diagnosis; and the DSM-IV requirement for clinically significant impairment in social, occupational, or other important areas of functioning is not included in ICD-10.
Diagnosis of Asperger syndrome can be tricky as there is a lack of standardized diagnostic screening for the disorder. According to the US National Institute of Neurological Disorders and Stroke, physicians look for the presence of a primary group of behaviors to make a diagnosis such as abnormal eye contact, aloofness, failure to respond when called by name, failure to use gestures to point or show, lack of interactive play with others, and a lack of interest in peers.
Reliability
The diagnoses of AS or high-functioning autism (HFA) are sometimes used interchangeably; the same child can receive different diagnoses depending on the screening tool and the individual administering the test. Diagnoses may be influenced by non-technical issues, such as the availability of government benefits for one condition but not the other. Advocacy and parent support organizations have proliferated around the concept of AS, and there are indications that this has resulted in more frequent diagnoses of AS, which may be given as a "residual diagnosis" to children of normal intelligence who do not meet diagnostic criteria for autism but have some social difficulties. Conversely, the cost of screening and diagnosis and the challenge of obtaining payment can inhibit or delay diagnosis.