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Pervasive Developmental Disorder, Not Otherwise Specified is a "subthreshold" condition in which some - but not all - features of autism or another explicitly identified Pervasive Developmental Disorder are identified. PDD-NOS is often incorrectly referred to as simply "PDD." The term PDD refers to the class of conditions to which autism belongs.

PDD is NOT itself a diagnosis, while PDD-NOS IS a diagnosis.

A brief description of the condition follows:

The definition of "subthreshold" PDD (PDD-NOS) is essentially a negative one; i.e., for individuals with a disorder with some features suggesting autism, but which does not meet full criteria. Although probably relatively common, research on this condition is, paradoxically, highly limited.

The term Pervasive Developmental Disorder - Not Otherwise Specified (PDD-NOS; also referred to as "atypical personality development", "atypical PDD", or "atypical autism") is included in DSM-IV to encompass cases where there is marked impairment of social interaction, communication, and/or stereotyped behavior patterns or interest, but when full features for autism or another explicitly defined PDD are not met. It should be emphasized that this ''subthreshold'' category is thus defined implicitly, that is, no specific guidelines for diagnosis are provided. While deficits in peer relations and unusual sensitivities are typically noted, social skills are less impaired than in classical autism. The lack of definition(s) for this relatively heterogeneous group of children presents problems for research on this condition.

The limited available evidence suggest that children with PDD-NOS probably come to professional attention rather later than is the case with autistic children, and that intellectual deficits are less common.

Case Illustration

Leslie was the oldest of two children. She was noted to be a difficult baby who was not easy to console but whose motor and communicative development seemed appropriate. She was socially related and sometimes enjoyed social interaction but was easily overstimulated. She was noted to exhibit some unusual sensitivities to aspects of the environment and at times of excitement exhibited some hand flapping. Her parents sought evaluation when she was 4 years of age because of difficulties in nursery school. Leslie was noted to have problems with peer interaction. She was often preoccupied with possible adverse events. At evaluation she was noted to have both communicative and cognitive functions within the normal range.

Although differential social relatedness was present, Leslie had difficulty using her parents as sources of support and comfort. Behavioral rigidity was noted, as was a tendency to impose routines on social interaction. Subsequently Leslie was enrolled in a therapeutic nursery school where she made significant gains in social skills. Subsequently she was placed in a transitional kindergarten and did well academically, although problems in peer interaction and unusual affective responses persisted. As an adolescent she describes herself as a "loner" who has difficulties with social interaction and who tends to enjoy solitary activities.