I have observed a lot of confusion over these terms. When I diagnose someone with an autistic spectrum disorder, I try to explain the above terms so as to avoid the confusion. I have also interviewed patients and parents of patients who have already been diagnosed, but still are confused. Either no one took the time to explain what the terms mean, or it was explained, but not enough of it was absorbed by the listener. Sometimes I see eyes glass over when I try to explain these terms.

Pervasive Developmental Disorders (PDD) was the official label given to autistic disorders in 1980 and thereafter. Developmental disorders are inborn and often inherited. The word pervasive was used as individuals diagnosed with a PDD have problems in many areas: mainly social relatedness, communication and in their play, activities and interests. PDD was first used in the third edition of the Diagnostic and Statistical Manual (DSM-III), published in 1980. Prior to this, in the DSM-II that was published in 1968, an autistic disorder was con­sid­ered a form of childhood schizophrenia even though at that time, and more so through the 1970s, more and more experts realized that an autistic disorder was independent from schizophrenia. The term PDD was chosen over Autistic Spectrum Disorder (ASD) for the DSM-III, but they are often interchangeable and both are used. In fact, the term spectrum from ASD is common shorthand today for autistic disorders. In the DSM-IV, published in 1994, autistic disorders were greatly expanded. Five PDDs were described with Rett’s Disorder, Childhood Disintegrative Disorder and Asperger’s Disorder included for the first time. The diagnosis of Autistic Disorder was close to the diagnosis of Infantile Autism that was first described in 1941.
The fifth category of PDD is Not Otherwise Specified (PDD-NOS), and there is much confusion about this. When one is given this diagnosis, it generally means that there are significant problems in the areas of relatedness, communication and interests/play, but there are characteristics of the case that differs from the criteria of any of the four specific PDDs. Generally, when one is diagnosed with PDD-NOS, the degree of delay, or impairment is not so severe as in Autistic Disorder and is more severe than in Asperger’s Disorder. It may interest the reader that most psychiatric categories, like the PDDs, have specific categories and a sort of residual NOS category. So, for example, we have Anxiety Disorder NOS, Mood Disorder NOS, Psychotic Disorder NOS, etc.

If you the reader has gotten this far, you may realize why eyes glass over when one tries to explain these terms. One final point here concerns how the terms autism and autistic are used. It appears to me that the terms, when not qualified, are used sometimes to refer to the whole spectrum and that sometimes they are used to refer specifically to Autistic Disorder. I think that when the words, “autism” and “autistic” are used care should be given so that it is clear what is meant by them.