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Autism: Diagnosis can vary greatly by site, clinician

Diagnosis is in the eye of the beholder, at least for autism spectrum classification, a recent study suggests.

Study results support eliminating the existing categories in favor of dimensional descriptions of affect, behavior, language, and cognition.

Researchers found a wide variation in the assignment of specific diagnostic categories of autism spectrum disorders (ASD) across 12 university-based centers, despite similar distribution of scores on standardized diagnostic instruments. Lead researcher Catherine Lord, PhD, of Weill Cornell Medical College, and colleagues write that “clinical distinctions among categorical diagnostic subtypes of autism spectrum disorders were not reliable even across sites with well-documented fidelity using standardized diagnostic instruments.”

The study included 2,102 participants aged between 4 and 18 years who met autism spectrum criteria on at least 2 diagnostic assessments and had a clinical diagnosis of an autism spectrum disorder (ASD)—autistic disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS), or Asperger syndrome. Children were excluded if they had significant hearing, vision, or motor problems; a nonverbal mental age of less than 18 months; or several other conditions likely to affect interpretation of behavioral data. Each center had between 97 and 229 participants.

Researchers found significant differences in the proportion of participants assigned to each ASD diagnostic category by experienced clinicians. Two sites diagnosed less than half of the children with autistic disorder, whereas 1 site diagnosed all participants with autistic disorder. Two sites gave more than 40% of their participants a diagnosis of PDD-NOS.

Across the 12 sites, the percentage of children diagnosed with Asperger syndrome ranged from 0% to 21%. In contrast to differences indicated by these best-estimate clinical diagnoses, the sites showed no statistically significant differences in ASD diagnostic classifications on the basis of results of standardized instruments.

"Relationships between clinical diagnoses and standardized scores, particularly verbal IQ, language level, and core diagnostic features, varied across sites in weighting of information and cutoffs,” said the researchers. In addition, regional differences could affect diagnoses. "For example, in some regions, children with diagnoses of autistic disorder receive different services than do children with other ASD diagnoses; elsewhere, autistic disorder diagnoses may be avoided as more stigmatizing than diagnoses of PDD-NOS or Asperger syndrome."

Best-estimate clinical diagnoses of specific ASD have been considered the diagnostic gold standard. Based on their research, the investigators conclude that “the conceptualization and measurement of ASD as a behavioral diagnosis, based on different dimensions (eg, social communication and repetitive behaviors) that are strongly influenced by intelligence and language skills, may be more useful” than clinical categorical diagnoses of autistic disorder, PDD-NOS, or Asperger syndrome.

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