Clinical Description of Preschoolers with Pervasive Developmental Disorder Not Otherwise Specified

Background: The most frequently diagnosed pervasive developmental disorder (PDD) subtype is PDD-NOS, yet it is the least well characterized. Research on the boundaries between PDD-NOS and other PDD subtypes has been inconclusive. Studies that have compared different PDD subtypes in terms of external behavioral criteria have yielded discrepant results. Such inconclusive results may be due to unreliable diagnostic criteria, the failure to control for age and intellectual functioning, and the nature of contrast groups. Refining PDD-NOS is of significant importance in understanding the etiology and management of PDDs. 

Objectives: The purpose of the current study was to provide a clinical description of preschoolers with PDD-NOS. Profiles of adaptive and problem behavior were compared to those of youngsters with autism and other developmental disabilities (DD) with behavior profiles similar to PDDs.

Methods: Data were obtained at a tertiary autism diagnostic specialty clinic. Data continue to be collected at the time of this writing. A multidisciplinary team assessed the participants and diagnoses were confirmed using the ADOS. Participants were between the ages of 23-69 months (mean=42.4 months, SD=14.1 months). The sample included 124 preschoolers (n=65 DD, n=37 autism, n=22 PDD-NOS).  Analyses were conducted on the entire sample and after individually matching children with PDD-NOS to those from the other groups on NVIQ, age, and gender (n=18 per group). Adaptive behavior was assessed with the Scales of Independent Behavior–Revised (SIB-R) and problem behaviors were assessed with parent and teacher versions of the Child Behavior Checklist (CBCL). 

Results: Analyses on the entire group indicated that children with PDD-NOS did not differ from the other groups in terms of adaptive behavior. Parent CBCL ratings indicated that preschoolers with PDD-NOS scored significantly higher than the DD group on the PDD syndrome scale (p=.02), as well as on several items at p<.01: "avoids eye contact," "upset by new people or situations," and "too shy or timid."  Teacher CBCL ratings indicated higher scores on only two items at p<.01: "disturbed by change in routine" and "strange behavior."  When children were matched on NVIQ, age, and gender, groups did not differ from each other in terms of adaptive behavior or behavior problem domain scores.  The only significant difference was that preschoolers with PDD-NOS scored significantly higher than preschoolers with DD on the item "disturbed by change in routine" (p=.007).

Conclusions: Data suggested few differences in adaptive and behavior problems between groups when controlling for level of functioning and age. The current study was the first to provide a clinical description of preschoolers with PDD-NOS by comparing them to diagnostically similar groups matched on level of functioning and age.  Further studies should continue to investigate the impact of level of functioning on the nosology of PDDs.