Clinicians use criteria from a collection of guidelines called the Diagnostic and Statistical Manual of Mental Disorders (DSM) to diagnose individuals with autism, among other psychiatric conditions. Before 2013, the 4th edition of the DSM (DSM-4) was used.

When the 5th edition of the DSM (DSM-5) was published, some diagnostic and classification changes were made to some conditions based on new research and clinical recommendations. Autism was one of these conditions.

This article explores how Autism used to be classified, and is classified today.

How the DSM-4 classified Autism

Published in 1994 and active until 2013, the DSM-4 recognized what we now call Autism as Autistic Disorder.

Autistic disorder was categorized as a pervasive developmental disorder (PDD), a term used to describe conditions characterized by delays in social and communication skills.

Autistic disorder was further classified into a sub-category of PDDs known as ‘Autism spectrum disorder’.

DSM-4 and Autism Spectrum Disorder

This sub-category of PDDs included the following conditions:

• Autistic disorder
• Asperger’s disorder
• Pervasive developmental disorder, not otherwise specified (PDD-NOS)

So, how were these three conditions different from each other?

Asperger’s disorder was distinguished from Autistic disorder in the DSM-4 due to a couple of factors:

• No clinically significant delays or abnormalities in language acquisition
• No clinically significant delays in cognitive development within the first three years of life

PDD-NOS was distinguished from Autistic disorder and Asperger’s disorder through its use to describe conditions with “a severe and pervasive impairment in the development of reciprocal social interaction… or with the presence of stereotyped behavior, interests, and activities, but the criteria are not met for a specific pervasive developmental disorder”.

PDD-NOS encompassed presentations considered to be “atypical Autism”, which did not meet the criteria for Autistic disorder due to any of the following criteria:

• Late age of onset
• Atypical symptoms
• Too few symptoms or symptoms with minimal severity

DSM-4 and other Pervasive Developmental Disorders

There were other PDDs that did not have their own sub-category, including Rett’s disorder and Childhood disintegrative disorder (CDD).

Rett’s disorder is a genetic condition characterized by multiple deficits or regressions after a period of normal functioning or development, usually around age one to two years. Children with Rett’s disorder develop Autistic-like behaviors; however, only females are born with the condition.

The DSM-4 described Rett’s disorder as different from Autistic disorder because of this pattern of its pattern of inheritance, and the fact that children with Rett’s disorder develop specific symptoms that don’t usually affect Autistic people specifically, like slowed rate of head growth and decreased mobility.

CDD is a condition in which development and previously acquired skills regress after birth, but in this case, it’s after at least two years of normal development. This can lead to a presentation of Autistic-like behaviors.

In the DSM-4, it was distinguished from Autistic disorder because Autistic disorder usually presents with developmental changes within the first year of life.

How the DSM-5 classifies Autism

The DSM-5 no longer groups developmental conditions under the label of ‘pervasive developmental disorders.’

Instead, the new edition of the diagnostic manual introduced Autism spectrum Disorder (ASD) as a condition in itself, rather than a categorization.

ASD provides a single name and set of criteria for the previously defined conditions of Asperger’s disorder, Autistic disorder, PDD-NOS, CDD, and Rett’s disorder.

Two core symptom domains characterize ASD:

• Deficits in social communication and interaction
• Restricted repetitive patterns of behavior, interests, and activities.

Some of these conditions had in the past been known by other names, which the DSM-5 now considers ASD. These included early infantile Autism, childhood Autism, Kanner’s Autism, high-functioning Autism, and atypical Autism.

The change in criteria meant that some people no longer met the threshold for diagnosing what was previously considered a pervasive developmental disorder. For this subset of individuals, a new condition was classified as social communication disorder (SCD).

Why did the DSM-5 make this change?

The reclassification was performed due to the large crossover between these conditions, which may have affected some people’s ability to receive an accurate diagnosis. New research that provided updated information about the symptoms and presentations of these previously identified conditions bolstered this.

Summary

In short, Autism used to be one of many conditions known as pervasive developmental disorders. It was grouped in a sub-category known as Autism Spectrum Disorders, along with Asperger’s disorder and PDD-NOS. Now, Autism Spectrum Disorder is a single condition that encompasses various presentations that affect social communication, social interaction, and patterns of behavior, interests, and activities.