The DSM-5, which is the Diagnostic and Statistical Manual of Mental Disorders for the diagnosis and treatment plan development for many developmental and mental health disorders, notes that there are several subtypes of autism spectrum disorder. Each manifests symptoms of differing severity and might require a specialized diagnostic process for a customized treatment plan.

Atypical autism, which is often classified as “Pervasive Developmental Disorder Not Otherwise Specified” (PDD-NOS), was originally diagnosed in the past to classify children who had some, but not all, of the symptoms of autism. However, as the diagnostic manual has advanced through its fifth edition, the specific terms have since been phased out as the definition of autism spectrum disorder.

The updated version of the DSM-5 defines ASD’s subtypes to include a broader range of symptoms that fall under the larger umbrella of autism spectrum disorder.

Under the DSM-5 autism’s various symptoms and their severity is categorized into a broader spectrum of behaviors and characteristics whose severity is classified by three levels of support. This means that many individuals who were previously diagnosed with PDD-NOS before the updated publishing of the DSM-5 in 2013 would now be diagnosed with autism spectrum disorder.

To better understand the symptomatic differences, diagnosis, and how things like ABA therapy can help, we’ll need to take a granular look at some important details.

The Evolution of ASD and PDD-NOS Diagnosis

The original DSM was published way back in 1952 by the American Psychiatric Association. At that time it outlined the criteria by which psychiatric and mental health disorders were diagnosed. Over the years updated editions of the DSM have been published to help clinicians better diagnose and treat patients with mental and behavioral health disorders.

In the original DSM Autism was classified as its own technical diagnosis in the DSM-3, which was published in 1980. Before that time children with behaviors that were similar to autism were often diagnosed as having juvenile schizophrenia!

In 1994 the updated DSM-4 was published which divided autism into five separate diagnostic categories. This included autistic disorder, Asperger syndrome, and PDD-NOS.
At that time the diagnostic recommendations made by the DSM-4 required that a child had to meet three diagnostic criteria to be confirmed for autism. This was:

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

At that time, a PDD-NOS required that a child only had to meet two criteria, one of which must be impairments in social interactions. At the same time schizophrenia, schizotypal personality disorder and other mental health conditions such as avoidant personality disorder needed to be ruled out before the clinician could assert a positive diagnosis for autism of PPD-NOS.

At that time, PDD-NOS was often considered to be a subthreshold of autism spectrum disorder which is sometimes referred to as “Atypical Autism.” This classification suggested a milder form of autism, which some today might refer to as high-functioning autism.

What Are Pervasive Developmental Disorders?

Pervasive developmental disorders (PDD) and (PDD-NOS) are typically characterized by impaired communication and socialization skills. In some cases, this can include Asperger syndrome as well as Rett syndrome and sometimes even childhood disintegrative disorder.

What Causes Autism?

The fifth edition of the DSM, which is now known as the DSM-5 was published in 2013. At that time, the APA decided to integrate all five autism categories into a single diagnostic category which is now known as “Autism Spectrum Disorder.”

This shift in definition essentially described autism as a condition with a relatively narrow list of characteristics and behaviors, while simultaneously acknowledging that ASD comes in many different forms. It also recognized that symptoms could vary dramatically from one individual to another, which often required a granular approach to confirming the diagnosis.

This means that for families today there is now a single diagnosis of ASD which can replace the different subcategories that were implemented in the DSM-4.

This included observations on different symptomatic categories such as:

  • Social-Communication Skill Challenges
  • Children and young adults with ASD often manifested some of the following issues to varying degrees.
  • Rarely using language to communicate with others
  • Never or barely responding when spoken to
  • Infrequently using gesturing like waving or pointing as forms of communication
  • Limited facial expressions
  • Struggling to engage in imaginative play
  • Not sharing interests or recalling events or achievements
  • Not showing interest in making friends
  • General disinterest in interacting with others

Restricted, Repetitive, and Sensory Behaviors or Interests

Many children with a confirmed diagnosis for ASD also showed obsessive attachment to objects or sensations such as:

  • Repeatedly lining up toys in a specific way
  • Repeatedly flicking switches
  • Repeatedly spinning objects
  • Repetitive speech
  • A very narrow and/or intense interests
  • Needing things to happen in a routine manner
  • Struggling or acting out against changing schedules
  • Intense reactions to certain sounds, textures, tastes, smells, or sights

How Atypical Autism Spectrum Disorder Is Diagnosed Today

Atypical autism sits somewhat outside of the current definition of autism spectrum disorder when it comes to the way mental health professionals address the severity of the individual’s symptoms. Before the DSM-5 the treatment of PDD-NOS was almost identical to the treatment of Asperger’s syndrome as both were often seen as simply being milder forms of autism. When the truth is that PDD-NOS might have milder symptoms, it doesn’t necessarily mean that it is any less disabling. Indeed there are some individuals with PDD-NOS who are severely disabled.7

Today the DSM-5 recognizes three different levels of Atypical Autism (PDD-NOS) they are:

Level 1 ASD

indicates a high level of functioning where assistance may be needed to overcome challenges with social connections, schedules and organization, and nuanced communication.

Level 2 ASD

is classified as an individual who needs a significant amount of structured support to overcome problems with things like spatial awareness, hypersensitivity, thought fixation, and gaps in social skills, among others.

Levels 3 ASD

is often reserved for individuals who need very substantial support for severe symptoms of autism spectrum disorder. To the degree that the person’s ability to communicate, avoid repetitive behaviors, or deal with sensory overload is drastically compromised.