What Is Atypical Autism?

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Atypical autism, or pervasive developmental disorder not otherwise specified (PDD-NOS), was a diagnosis used between 1994 and 2013. It first appeared in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) to encompass the many children who had some, but not all, symptoms of autism.

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The DSM-5, published in 2013, updated the diagnosis of autism to include a broader range of symptoms that fall under autism spectrum disorder (ASD), along with three levels to indicate support needs. Level 1 requires the least support, while Level 3 requires the most support.

Most people who previously were given a diagnosis of PDD-NOS would likely receive a diagnosis of ASD under the new diagnostic criteria.

Autism and the DSM

The DSM is the American Psychiatric Association's manual that lists all mental and developmental disorders. There are five versions of the DSM, dating back to 1952.

Unlike physical disorders, mental and developmental disorders are often based on social norms and each DSM update has new or revised diagnostic criteria and disorders.

Autism was first classified as its own diagnosis in the DSM-III, published in 1980. Prior to that, children with autism-like behaviors were given a diagnosis of childhood schizophrenia.


The DSM-IV was published in 1994 and divided autism into five separate diagnostic categories. Among these were autistic disorder, Asperger's syndrome, and PDD-NOS.

The term "autism spectrum" in the DSM-IV referred to 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).

PDD-NOS referred to "presentations that do not meet the criteria for autistic disorder because of late age of onset, atypical symptomatology, subthreshold symptomatology, or all of these."

The two main diagnostic criteria include:

  • Severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills;
  • Or 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.

Characteristics of PDD-NOS are similar to autism but tend to be milder and include:

  • Atypical or inappropriate social behavior
  • Uneven development of skills, such as fine or large motor skills, visual or spatial organization, or cognitive skills
  • Delays in speech or language comprehension
  • Difficulty with transitions
  • Deficits in nonverbal and/or verbal communication
  • Increased or decreased sensitivities to taste, sight, sound, smell and/or touch
  • Repetitive or ritualistic behaviors

A PDD-NOS or atypical autism diagnosis meant there were too few symptoms to be diagnosed with autistic disorder or Asperger's syndrome, or symptoms that were not consistent with a diagnosis of Rett syndrome or childhood disintegrative disorder.

DSM-5: Autism Spectrum Disorder

When the DSM-5 was published 2013, it made the rather momentous decision to collapse all five of the autism diagnoses from DSM-IV into a single diagnostic category: autism spectrum disorder (ASD).

A diagnosis of PDD-NOS is under the autism umbrella in the DSM-IV, and, according to the DSM-5, a diagnosis made under DSM-IV cannot be revoked. However, a person diagnosed with PDD-NOS may or may not fit the current criteria for autism.

According to research published by Journal of the American Academy of Child and Adolescent Psychiatry in 2014, the majority of patients with a PDD-NOS diagnosis (63%) meet the criteria for autism spectrum disorder as outlined in DSM-5.

The study also found that most prior PDD-NOS diagnoses that don't meet the current ASD criteria fit a diagnosis of social communication disorder (32%). The remaining 2% could be diagnosed with attention-deficit/hyperactivity disorder (ADHD) and anxiety disorder.

Atypical Autism

Other terms to describe PDD-NOS besides atypical autism include autistic tendencies, and autistic traits.

While some people with PDD-NOS have milder autism symptoms, that does not necessarily mean it is any less disabling. It is, in fact, quite possible to have this diagnosis and be severely disabled.

A study published in the Journal of the American Academy of Child and Adolescent Psychiatry compared individuals with PDD-NOS to individuals with autism and Asperger's syndrome, and found children with PDD-NOS could be placed into one of three subgroups:

  • A high-functioning group (24%) with symptoms of Asperger's syndrome, but had a transient language delay or mild cognitive impairment
  • A subgroup with symptoms resembling autism (24%) but who had late age of onset, or had severe cognitive delays, or were too young to potentially meet the full diagnostic criteria for autism
  • A group (52%) not fulfilling the criteria for autism because of fewer stereotyped and repetitive behaviors.

In terms of the 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 Asperger's syndrome.

In contrast, the PDD-NOS group had fewer autistic symptoms, especially repetitive stereotyped behaviors, than the other groups.


Regardless of the subcategory of an autism spectrum diagnosis, the treatments recommended are likely to be very similar no matter what the official diagnosis: intensive behavioral and/or developmental therapy, along with speech, occupational, and physical therapies, and social skills classes for older children.

Living With Autism

Autism presents differently in individuals and the autism spectrum covers a wide range of autism profiles and levels of disability associated with ASD. While autism is typically diagnosed in children, it is not a disorder you outgrow.

While early intervention and treatment can help to teach coping strategies, adults with autism and PDD-NOS can still struggle with social interactions, behavioral challenges, and perceptual problems.

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13 Sources
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