What are Autism Spectrum Disorders? A history of Autism diagnosis

The criteria clinicians use to diagnose an individual with Autism, amongst other psychiatric conditions, comes from a collection of guidelines called the Diagnostics and Statistics Manual (DSM). Prior to 2013, the 4th edition of the DSM (DSM-4) was used for diagnostic purposes.

When the 5th edition of the DSM (DSM-5) was published, there were a couple of changes made based on new research and clinical recommendations, which changed the way that some conditions were diagnosed and classified. Autism was one of these conditions.

This article will explore how Autism used to be classified, and how it 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 disorders’.

DSM-4 and Autism Spectrum Disorders

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 3 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 deviance in language acquisition
  • No clinically significant delays in cognitive development within first 3 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 that were considered to be “Atypical Autism”, which did not meet the criteria for Autistic disorder due to any of the below criteria:

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

DSM-4 and other pervasive developmental disorders

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

Rett’s disorder is a genetic condition characterized by the development of multiple deficits or regressions after a period of normal functioning or development, usually around age 1 to 2. Children with Rett’s disorder develop Autistic-like behaviors. Only females are born with the condition.

The DSM-4 described Rett’s disorder as different to Autistic disorder because of this 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 also a condition in which development and previously acquired skills regresses after birth, but in this case, it’s after at least 2 years of normal development. This can lead to a presentation of Autistic-like behaviors.

In the DSM-4, it was distinguished from Autistic disorder due to the fact that Autistic disorder usually presented 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.

ASD is characterized by two core symptom domains:

  • 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 also clarified now exist as ASD. These included early infantile Autism, childhood Autism, Kanner’s Autism, high-functioning Autism, and atypical Autism.

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

Why did the DSM-5 make this change?

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


A side-by-side comparison of the differences between the DSM-4 and DSM-5 classifications of Autism and related disorders.

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

Olivia Holland
Medical Writer