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Specifying PDD-NOS: A Comparison of PDD-NOS, Asperger Syndrome, and Autism

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ABSTRACT

Objective

To describe the clinical characteristics of children given a diagnosis of pervasive developmental disorder-not otherwise specified (PDD-NOS) by expert clinicians and to compare these to the clinical characteristics of children given a diagnosis of autism and Asperger syndrome (AS).

Method

Two hundred sixteen children with autism, 33 with AS, and 21 with PDD-NOS were compared on measures of level of functioning (communication, daily living and social skills, IQ, and age of acquisition of language) and on various symptoms of autism (impaired communication and reciprocal social interaction and a preference for repetitive and stereotyped activities).

Results

In terms of level of functioning measures, the PDD-NOS children had scores that were between those of the children with autism and those of the children with AS. In contrast, the PDD-NOS group had fewer autistic symptoms, especially repetitive stereotyped behaviors, than both the autism and AS groups (χ2 = 11.06, p = .004). Children with PDD-NOS could be placed into one of three subgroups: a high-functioning group (24%) who resembled AS but had transient language delay or mild cognitive impairment; a subgroup resembling autism (24%) but who had late age of onset or too severe cognitive delays or were too young to potentially meet the full diagnostic criteria for autism; and a group (52%) not fulfilling the criteria for autism because of fewer stereotyped and repetitive behaviors.

Conclusions

With some revision to current diagnostic criteria, a more homogenous atypical group with significant impairments in social-communication but fewer repetitive behaviors can be differentiated from the more nonspecific PDD-NOS group. This differentiation may lead to better reliability in diagnosis and to further progress in studies of etiology.

Section snippets

PDD-NOS and ADHD

Barkley (1990) reported that it is common for children with PDD-NOS to be initially given a diagnosis of ADHD. Jensen et al. (1997) reported that 74% of the children in their study diagnosed with PDD-NOS were originally diagnosed with ADHD. Another study showed that children with PDD-NOS and ADHD did not differ with respect to total number of autistic symptoms, general psychopathology, or attention difficulties (Luteijn et al., 2000). This overlap may be because some early signs of ADHD and

Participants

Two hundred seventy children participating in a genetic study of the ASDs and diagnosed using a consensus best-estimate method were included in this study. Families with one or more child affected by PDD as well as singleton families were included. Participants were recruited from across Ontario through a regional diagnostic center for PDD, through physicians and other health care professionals who referred children to this center, and through parent support groups. Further participants were

Comparison on Level of Functioning

The mean scores of each group with respect to level of functioning are shown in Table 1 (A). An omnibus one-way ANOVA was performed initially to investigate differences between the three groups as a whole. There were significant differences between the groups on each measure. Therefore, follow-up analysis compared the PDD-NOS group to the AS group and autism group, respectively, using the LSD method. No differences were observed between the PDD-NOS and AS groups on any variable measuring level

DISCUSSION

The objective of this paper was to explore how expert clinicians use the DSM-IV criteria of PDD-NOS. This was not a study of the diagnostic “validity” of the category, since the clinical differences observed between this group and the children with autism and AS depended critically on how the groups were defined in the first place. We hoped that by carefully characterizing children given this diagnosis, it might be possible to derive more precise criteria for PDD-NOS so that the reliability of

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    This project was supported by the Canadian Institutes of Health Research (CIHR). Dr. Szatmari was supported by an award from CIHR; Drs. Goldberg and Zwaigenbaum were supported by fellowship awards from the Ontario Mental Health Foundation.

    The authors thank the parents and children in the study for their continued participation and support.

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