What Is Atypical Autism?

Atypical autism, also known as pervasive developmental disorder not otherwise specified (PDD-NOS), was a diagnosis previously used to classify children who had some, but not all, of the symptoms of autism. The terms have since been phased out as the definition of autism has changed in recent years.

The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) updated the definition of autism in 2013 to include a broader range of symptoms that fall under the larger umbrella of autism spectrum disorder (ASD).

Under this new definition, autism is regarded as a broader spectrum of behaviors and characteristics whose severity is classified by three levels of support. As such, people previously diagnosed with PDD-NOS would now be diagnosed with ASD.

This article explains how and why PDD-NOS was combined into the diagnosis of ASD and what this means to children and adults living with autism.

How the Definition of Autism and PDD-NOS Evolved

The DSM, published by the American Psychiatric Association (APA), outlines the criteria by which psychiatric and mental disorders are diagnosed. There are five versions of the DSM, dating back to 1952.

Autism was first classified as its own diagnosis in the DSM-3, published in 1980. Prior to that, children with autism-like behaviors were given a diagnosis of childhood schizophrenia.

The DSM-4, published in 1994, divided autism into five separate diagnostic categories. Among these were autistic disorder, Asperger syndrome, and PDD-NOS.

For autism to be diagnosed under the DSM-4, a child had to meet three diagnostic criteria:

• Impairments in social interaction
• Impairments in communication
• Repetitive behaviors

For PDD-NOS to be diagnosed, a child only needed to meet two criteria, one of which must be impairments in social interactions. On top of this, schizophrenia, schizotypal personality disorder (STPD), and avoidant personality disorder (APD) had to be ruled out before the diagnosis could be considered definitive.

PDD-NOS, also known as subthreshold autism or atypical autism, was used when some but not all symptoms of autism were present. It suggested a milder form of autism, which some today might refer to as high-functioning autism (though this term itself is controversial).

Changing Definitions: DSM-5 and Autism Spectrum Disorder

When the DSM-5 was released in 2013, the APA made the decision to fold all five autism categories into a single diagnostic category known as autism spectrum disorder (ASD).

Rather than describing autism as a condition bound by a relatively narrow list of characteristics and behaviors, the DSM-5 acknowledges that ASD comes in many different forms.

Today, there is a single diagnosis of ASD that replaces the different subcategories used in the DSM-4. The DSM-5 criteria are based on difficulties in two specific areas:

Social Communication Skills

Signs of impairment of social communications skills in children with ASD include:

• Rarely or never using language to communicate with others
• Rarely or never responding when spoken to
• Rarely or never using gesturing like waving or pointing
• Limited facial expressions
• Rarely or never engaging in imaginative play
• Not sharing interests or recalling events or achievements
• Not showing interest in making friends or interacting with others

Restricted, Repetitive, and Sensory Behaviors or Interests

These are behaviors in which a child with ASD has a limited range of focus or interest and an often obsessive attachment to objects or sensations.

Examples include:

• Lining up toys in a specific way over and over again
• Repeatedly flicking switches or spinning objects
• Speaking in a repetitive way
• Having very narrow and/or intense interests
• Needing things to happen in the same way every time
• Difficulty switching out of patterned behaviors or changing schedules
• Intense reactions to certain sounds, textures, tastes, smells, or sights
  

Treatment of PDD-NOS vs. ASD

Another way that PDD-NOS stands outside of the current definition of ASD is how mental health professionals address the severity of the condtion. In the past, the treatment of PDD-NOS was largely the same as for Asperger's syndrome given that both were regarded as "milder" forms of impairment.

And, while it is true that people with PDD-NOS often have milder symptoms, that doesn't necessarily mean that it is any less disabling. In fact, some people with PDD-NOS are severely disabled.

As such, the DSM-5 has established three levels of ASD that reflect the amount of support that a person needs irrespective of the exact features of their condition:

• Level 1 ASD indicates a high level of functioning in which assistance may be needed to overcome challenges with social connections, schedules and organization, and nuanced communication.
• Level 2 ASD indicates the need for structured support to overcome problems with spatial awareness, sensory hypersensitivity, thought fixation, and gaps in social skills, among others.
• Levels 3 ASD indicates the need for substantial support when autism symptoms are severe and limit a person's ability to communicate, avoid repetitive behaviors, or deal with sensory overload.

Summary

Pervasive developmental disorder not otherwise specified (PDD-NOS)—also known as atypical autism—is an outdated term used when a child has some symptoms of autism but does not meet the criteria listed in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-4).

With the release of the DSM-5 in 2013, PDD-NOS has been folded into the larger category known as autism spectrum disorder (ASD). ASD is diagnosed based on a broader range of symptoms and classified based on its severity and the level of support a person needs in everyday life.

A Word From Verywell

Technically, most mental health professionals in the United States no longer diagnose children with atypical autism or PDD-NOS. That doesn't mean that the treatment approach or the need for treatment has changed.

Regardless of the category of diagnosis—whether PDD-NOS or ASD—the approach will likely involve behavioral and/or developmental therapy along with speech, occupational, and physical therapies, and social skills classes for older children.

The diagnosis of ASD simply acknowledges that autism is not one thing. Broadening the definition better ensures that people with mild autism don't "fall between the cracks" and can still get the individualized care and support they need.