Understanding Different Diagnoses on the Autism Spectrum

Understanding the Different Types of Autism: What the Diagnoses Mean

Autism is not a one-size-fits-all condition. It's a spectrum—a wide and varied range of neurological differences that affect how individuals communicate, process information, relate to others, and experience the world around them. While “Autism Spectrum Disorder” (ASD) is now the umbrella term used in most diagnostic settings, it’s important to understand that within this spectrum, there have historically been and still are specific subtypes and related conditions that can help provide clarity and context.

Let’s explore a few diagnostic categories and terms that have been associated with autism over the years. This overview is for informational purposes and is meant to broaden understanding—not to label or box anyone in.

1. PDD-NOS (Pervasive Developmental Disorder—Not Otherwise Specified)

PDD-NOS was once used to describe individuals who exhibited some symptoms of autism but didn’t meet the full criteria for Autistic Disorder or Asperger’s Syndrome. It was considered a “subthreshold” diagnosis—meaning that someone had clear developmental differences but didn’t fit neatly into another category.

This term was commonly used before the DSM-5 was released in 2013. Today, those previously diagnosed with PDD-NOS are generally considered to be on the autism spectrum under the broader ASD classification.

Common traits associated with PDD-NOS may have included:

• Delays in language development

• Difficulty with social interaction

• Sensory sensitivities

• Uneven skill development (strong in some areas, behind in others)

2. CDD (Childhood Disintegrative Disorder)

CDD is a very rare condition that typically appears after two to four years of normal development. A child with CDD may suddenly lose previously acquired skills in multiple areas, such as:

• Language

• Social abilities

• Motor skills

• Bowel or bladder control

The regression is profound and can be distressing for families. CDD has often been viewed as one of the most severe forms of the autism spectrum, although today it’s rarely diagnosed separately and is instead grouped under ASD.

3. PDA (Pathological Demand Avoidance)

PDA is not formally recognized in most diagnostic manuals, but it’s widely discussed, particularly in the UK. Individuals with PDA often experience extreme anxiety when asked to comply with everyday demands, even those they might otherwise enjoy.

This resistance isn’t rooted in defiance—it stems from a need to feel in control and reduce internal stress.

Common characteristics of PDA include:

• High levels of anxiety, especially around expectations

• Comfort with imaginative play

• Sudden mood swings

• Social strategies to avoid demands (distraction, negotiation, withdrawal)

Though not a standalone diagnosis in the DSM-5 or ICD-10, PDA is increasingly acknowledged as a profile within the autism spectrum.

4. Rett Syndrome

Rett Syndrome is a rare genetic neurological disorder that primarily affects girls. It is caused by mutations in the MECP2 gene and is not technically considered autism, though it was once classified under the Pervasive Developmental Disorders umbrella.

Children with Rett Syndrome typically develop normally for the first 6–18 months before experiencing a rapid decline in motor and cognitive skills.

Key signs include:

• Loss of purposeful hand skills (often replaced by repetitive hand-wringing)

• Loss of speech and social engagement

• Breathing irregularities

• Seizures and mobility challenges

Though it shares some similarities with autism, Rett Syndrome is now recognized as a separate condition due to its known genetic origin.

The Shift to a Unified Diagnosis: Autism Spectrum Disorder (ASD)

In 2013, the DSM-5 replaced the above terms with the single diagnosis of Autism Spectrum Disorder. This shift was made to reflect the growing understanding that autism exists along a continuum—rather than in separate, rigid categories.

Instead of labeling someone as having Asperger’s, PDD-NOS, or Autistic Disorder, clinicians now assess the level of support needed in various areas like communication, social behavior, and flexibility in thinking.

This unified approach allows for a more personalized view of autism, without relying on outdated terms or broad-functioning labels that can misrepresent a person’s abilities or needs.

Understanding the historical and related diagnoses of autism can help us see the full picture. Each person on the spectrum is unique—not only in their challenges but in their strengths, communication styles, and ways of thinking.

As terminology continues to evolve, the most important thing we can do is keep listening, learning, and respecting individual experiences. A diagnosis can offer clarity, but it should never define the whole person.