Specifying PDD-NOS: a comparison of PDD-NOS, Asperger syndrome, and autism.

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 (chi2 = 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.