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Date First Published: April 2, 2007

Pervasive Developmental Disorder Not Otherwise Specified: it’s a mouthful, a long and laborious phrase. What it means, in truth, is “kind of like autism, but not meeting enough criteria to qualify for the autism diagnosis.” Unlike the other pervasive developmental disorders, such as Autistic Disorder and Asperger’s Disorder, there is no lengthy list of criteria for PDD-NOS. Its description is covered in a single paragraph which mainly asserts what it is not:

"This category should be used when there is severe and pervasive impairment in the development of reciprocal social interaction associated with impairment in either verbal or nonverbal communication skills or with the presence of stereotyped behavior, interests, and activities, but the criteria are not met for a specific Pervasive Developmental Disorder, Schizophrenia, Schizotypal Personality Disorder, or Avoidant Personality Disorder. For example, this category includes “atypical autism” – presentations that do not meet the criteria for Autistic Disorder because of late age at onset, atypical symptomatology, or subthreshold symptomatology, or all of these." 1

Who ends up with this awkward designation? And what are the consequences of receiving it?

If a person has autistic-like behaviors and ways of taking in the world that impact functioning, but does not fully meet the criteria for autistic disorder or Asperger’s syndrome, he may receive the PDD-NOS diagnosis. PDD-NOS may be thought of as “subthreshold autism," or a diagnosis one can give a person who has “atypical symptomatology.” 2  In other words, when someone has an autistic “flavor” but some of their symptoms are mild, or they have severe symptoms in one area (like social deficits), but none in another key area (like restricted, repetitive behaviors), they may be given the PDD-NOS label.

On the positive side, the existence of the PDD-NOS category provides a way to name and include people who are on the autism spectrum but do not quite fit elsewhere. Some parents may even prefer the label, feeling it to be less stigmatizing than “autism."

On the negative side, PDD-NOS is rather non-specific.  If you stick too many variations of something in the same pot, you risk making the category less and less meaningful. For instance, researchers have found that clinicians can much more reliably diagnose autistic disorder and Asperger’s syndrome as compared to PDD-NOS. 3   “Reliable” here means that different clinicians, making an independent assessment of the same case, are likely to come up with the same diagnosis. The fact that they could not reliably diagnose PDD-NOS means that a parent who has received a diagnosis of PDD-NOS for their child, and seeks a second opinion, is not terribly likely to receive the same diagnosis again. In short, the category itself is not easy to pin down resulting in maximum confusion around diagnostic issues.

This fuzziness may impact other areas as well. Parents who were glad to receive a “less stigmatizing” PDD-NOS label for their child may find there is a downside: less understanding of the label by institutions, and a harder fight for services.

What might a person who has received a diagnosis of PDD-NOS look like? That will vary, of course, but in one study, researchers found that those with PDD-NOS could be placed in one of three very different subgroups: 4

  • A high-functioning group (24%) who resembled people with Asperger’s syndrome but had transient language delay or mild cognitive impairment (such that they could not receive the Asperger's diagnosis which requires no speech or cognitive delay).
  • A group (24%) who resembled people with autism but who had a late age of onset, or otherwise did not meet the criteria for autism.
  • A group (52%) who were autistic-like, but displayed fewer stereotyped and repetitive behaviors.

Research is needed to further investigate whether specific autism spectrum conditions, as yet unnamed, can be teased out of the catch-all category currently called PDD-NOS. There is no question that there are such conditions, that PDD-NOS (or whatever conditions we are bunching in that category for the moment) exists.

On the hypothetical autism spectrum, writes one researcher: “PDD-NOS is a paradoxical clinical entity. Despite its amorphous clinical boundaries and the subtlety of the clinical presentation, PDD-NOS is one of the most important PDDs. Its importance stems from its relationship to autism, its prevalence, and most of all, the impairment that it imparts to those who have it.”  5


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