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In a study conducted at 12 university-based research sites, there was wide variation in how best-estimate clinical diagnoses within the autism spectrum were assigned to individual children (Archives of General Psychiatry, online, Nov. 7, 2011).
While diagnostic instruments have been helpful in defining populations, merging samples, and comparing results across studies in the field of autism spectrum disorders (ASD), the gold standard has been best-estimate clinical diagnoses of specific disorders, including autistic disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS), and Asperger syndrome.
The lead investigator for the observational study was Catherine Lord, PhD, director of the Institute for Brain Development, a partnership of Weill Cornell Medical College, NewYork-Presbyterian Hospital and Columbia University Medical Center. She and colleagues set out to determine whether the relationships between behavioral appearance and clinical diagnoses of ASD vary across university-based sites.
The study included 2,102 participants (1,814 male) ages 4-18 who met autism spectrum criteria on two diagnostic assessments and had a clinical diagnosis of an ASD. The researchers collected demographic, diagnostic and developmental data for genetic research.
Clinical distinctions among categorical diagnostic ASD subtypes were not reliable, even across sites with well-documented fidelity using standardized diagnostic instruments, researchers reported. "Although distributions of scores on standardized measures were similar across sites, significant site differences emerged in best-estimate clinical diagnoses of specific autism spectrum disorders."
Relationships between clinical diagnoses and standardized scores - particularly verbal IQ, language level and core diagnostic features - varied across sites in the weighting of information and cut-offs.
Differences in diagnoses could reflect regional variations, the researchers suggested. "For example, in some regions children with diagnoses of autistic disorder receive different services than children with other ASD diagnoses. Elsewhere, autistic disorder diagnoses may be avoided as more stigmatizing than diagnoses of PDD-NOS or Asperger syndrome."
The study results have implications for revisions of current diagnostic frameworks, they pointed out. "Results support the move from existing subgroupings of ASD to dimensional descriptions of core features of social affect and fixated, repetitive behaviors, together with characteristics such as language level and cognitive function."
Clinicians typically administer a variety of tests or scales and use information from observations and parent interviews to classify individuals into subcategories listed in standard psychiatric diagnostic manuals.
"Clinicians at one center may use a label like Asperger syndrome to describe a set of symptoms, while those at another center may use an entirely different label for the same symptoms. This is not a good way to make a diagnosis," said Dr. Lord. "Autism spectrum disorders are just that - a spectrum of disorders. Instead of using subcategories, it would be better to simply report the results from agreed-upon tests and scales. This approach would provide more consistent and accurate information about individual patients."
The new study adds to previous evidence that standardized diagnostic instruments accurately predict who has autism and will continue to have it over time. It is also in line with recent skepticism about the value of categorical groupings of ASDs in standard diagnostic manuals, such as the Diagnostic and Statistical Manual of Mental Disorders IV-Text Revision (DSM-IV-TR) and the International Statistical Classification of Diseases.
"There has been a lot of controversy about whether there should be separate diagnoses for autism spectrum disorder, especially Asperger syndrome," Dr. Lord said. "Most of the research has suggested that Asperger syndrome really isn't different from other autism spectrum disorders."
The study participants were recruited from the Simons Simplex Collection, a multi-site project aimed at studying de novo genetic variations in families affected by ASD. The clinicians, who are experts in ASD, received training on how to administer and score the same set of cognitive tests and standardized instruments assessing social and communication skills and repetitive behavior, including the Autism Diagnostic Observation Schedule (ADOS) and the Autism Diagnostic Interview-Revised (ADI-R). However, they received no specific training in making best-estimate clinical diagnoses.
Diagnoses of specific categories of ASD varied dramatically from site to site across the country. For instance, clinicians at one site gave only a diagnosis of autistic disorder, while clinicians at other sites gave that diagnosis to fewer than half of the participants. The proportion of individuals receiving a diagnosis of Asperger syndrome ranged from zero to nearly 21 percent across sites.
These site differences were the second most important factor accounting for variation in the diagnoses, after social and communication deficits. However, the individuals with ASD did not vary significantly across sites in terms of their demographic information or developmental and behavioral characteristics, as measured by standardized instruments.
"The labels are pretty meaningless because people are using the same general terms as if they mean the same thing, when they really don't," Dr. Lord said. "Because clinicians may not be using labels appropriately or diagnosing accurately, they may not be getting a sense of children's strengths and weaknesses and what therapy is best for them."
Clinicians across centers varied in how they weighed different factors and in the thresholds they set to make diagnoses. Although verbal IQ strongly influenced diagnoses at most centers, there were striking differences in the cut-off points used at each site to classify individuals into specific categories. The effect of age on diagnoses and the specific age cut-off points also varied dramatically across sites.
"This doesn't make sense," Dr. Lord said. "You don't want to be told that you have a cold if you're 7 and a bacterial infection if you're 12, when you present with identical symptoms."
The variability in clinical diagnoses could reflect regional differences, she noted. For instance, services in some regions may be available only to children with a diagnosis of autistic disorder, but this diagnosis may be stigmatizing or limit school options in other regions. Clinicians also may vary in how they take into account an individual's level of irritability and hyperactivity when judging the severity of ASD.
Because of the inconsistencies in best-estimate clinical diagnoses, the use of standard diagnostic manuals to classify individuals into ASD subcategories should be reconsidered, Dr. Lord said. "It's very important for clinicians to use information from dimensions that directly relate to autism spectrum disorders, in addition to verbal IQ and the level of irritability and hyperactivity. The take-home message is that there really should be just a general category of autism spectrum disorder, and then clinicians should be able to describe a child's severity on these separate dimensions."
In future research Dr. Lord will work on improving diagnostic instruments - making them shorter, easier to use, and more appropriate for a wider variety of patients - and assessing whether certain dimensions are really distinct from one another. This work will build on her previous efforts in developing these commonly used scales.
Collaborating institutions were Columbia University Medical Center, the Simons Foundation, University of Michigan, Emory University School of Medicine, Marcus Autism Center, Children's Healthcare of Atlanta, Children's Hospital of Philadelphia, University of Washington in Seattle, Vanderbilt University Medical Center, Harvard Medical School, University of California-Los Angeles, Montreal Children's Hospital, University of Missouri, Baylor College of Medicine, University of Illinois, Cincinnati Children's Hospital Medical Center, University of Minnesota, and Indiana University.
This research was funded by the Simons Foundation and the National Institute of Mental Health.
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