What Was PDD-NOS, Also Known as Atypical Autism?

Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS)

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Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS), sometimes called atypical autism, was—for a relatively short time—a diagnostic category within the autism spectrum. PDD-NOS was "invented" to encompass the many children who had some, but not all, symptoms of autism. 

PDD-NOS is no longer a diagnostic category, though there are plenty of teens and young adults who received the diagnosis as toddlers.

A Short History of PDD-NOS

The DSM is the manual that lists all mental and developmental disorders. There are now 5 versions of the DSM, and each is quite different from the others. Mental and developmental disorders, unlike physical disorders, are often based on social norms; thus, for example, homosexuality was long considered to be a mental disorder but is no longer listed in the DSM. New disorders, such as hoarding, have been added.

PDD-NOS in the DSM-IV (After 2013)

The DSM-IV was written in 1994. In it, for the first and last time, autism was divided into five separate diagnostic categories. Among these were autistic disorder, Asperger syndrome, and PDD-NOS. In the DSM-IV, autism spectrum was another name for pervasive developmental disorders (PDDs), a category of diagnoses with certain symptomatic similarities Atypical autism was another name for one of the five official autism spectrum diagnoses : pervasive developmental disorder not otherwise specified (PDD-NOS).

Here is how PDD-NOS was differentiated from other PDDs:

This category should be used when there is a severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and activities are present, 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 of onset, atypical symptomatology, or subthreshold symptomatology, or all of these.

If your child was diagnosed with PDD-NOS (or "atypical autism"), it meant he or she had too few symptoms to be diagnosed with autistic disorder or Asperger syndrome, and the wrong symptoms to be diagnosed with Rett syndrome or Childhood Disintegrative Disorder. Yet he had received an official medical diagnosis which meant that he had significant pervasive developmental disorders.


In 2013, the DSM-5 was published. Developers of the DSM-5 made the rather momentous decision to collapse all five of the autism diagnoses from DSM-IV into a single diagnostic category: autism spectrum disorder. As a result, people with the other four diagnoses suddenly lost their diagnosis.

This change, of course, begs the question: if my child has a diagnosis of "atypical autism" or PDD-NOS, is he autistic? The answer is yes... and no.

YES: According to the DSM-IV, a child diagnosed with PDD-NOS was, in fact, diagnosed as having an autism spectrum disorder. And, according to the DSM-5, if your child was diagnosed with any form of autism under the DSM-IV, that diagnosis cannot be revoked.

NO: If your child was diagnosed with PDD-NOS, he or she did not have the precise set of symptoms expected of a person with autism. As a result, if he or she were to be evaluated today, there is a chance that he or she would NOT fit new criteria for autism.

Do People Who Were Diagnosed with PDD-NOS Have  Milder Symptoms?

In fact, a diagnosis of PDD-NOS doesn't necessarily mean that the child's symptoms are milder or less disabling, only that they don't completely fall within the diagnostic criteria for another related disorder such as Asperger syndrome or autistic disorder. In other words, it's quite possible to have an atypical autism/PDD-NOS diagnosis and be severely disabled.

Interestingly, though, many children and adults who received atypical autism/PDD-NOS diagnoses do in fact have relatively mild symptoms. A study comparing individuals with atypical autism/PDD-NOS diagnoses to individuals with other, more specific autism spectrum diagnoses came up with this conclusion:

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.

While the categories of the autism spectrum are very difficult to distinguish, in a sense it really doesn't matter which diagnosis your child receives. That's because the treatments recommended for your child's developmental differences are likely to be very similar no matter what the official autism spectrum diagnosis: intensive behavioral and/or developmental therapy, along with speech, occupational and physical therapies. As your child grows a bit older, he or she will also almost certainly be recommended to some form of social skills therapy as well.

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Article Sources
  • Allen DA, Steinberg M, Dunn M, Fein D, Feinstein C, Waterhouse L, Rapin I. "Autistic disorder versus other pervasive developmental disorders in young children: same or different?" Eur Child Adolesc Psychiatry. 2001 Mar;10(1):67-78.
  • National Institute of Child Health and Human Development. Autism Spectrum Disorders (ASDs)Fact Page.
  • Walker DR, et al. "Specifying PDD-NOS: a comparison of PDD-NOS, Asperger syndrome, and autism." J Am Acad Child Adolesc Psychiatry. 2004 Feb;43(2):172-80.