Several related disorders are grouped under the broad heading "Pervasive Developmental Disorder" or PDD-a general category of disorders which are characterized by severe and pervasive impairment in several areas of development (American Psychiatric Association 1994). A standard reference is the Diagnostic and Statistical Manual (DSM), a diagnostic handbook now in its fourth edition. The DSM-IV lists criteria to be met for a specific diagnosis under the category of Pervasive Developmental Disorder.
 
Diagnosis is made when a specified number of characteristics listed in the DSM-IV are present. Diagnostic evaluations are based on the presence of specific behaviors indicated by observation and through parent consultation, and should be made by an experienced, highly trained team. Thus, when professionals or parents are referring to different types of autism, often they are distinguishing autism from one of the other pervasive developmental disorders.
 
Individuals who fall under the Pervasive Developmental Disorder category in the DSM-IV exhibit commonalties in communication and social deficits, but differ in terms of severity. We have outlined some major points that help distinguish the differences between the specific diagnoses used:
 
Autistic Disorder
Impairments in social interaction, communication, and imaginative play prior to age 3 years. Stereotyped behaviors, interests and activities.
 
Asperger's Disorder
Characterized by impairments in social interactions and the presence of restricted interests and activities, with no clinically significant general delay in language, and testing in the range of average to above average intelligence.
Pervasive Developmental Disorder- Not Otherwise Specified
(Commonly referred to as atypical autism) a diagnosis of PDD-NOS may be made when a child does not meet the criteria for a specific diagnosis, but there is a severe and pervasive impairment in specified behaviors.
 
Rett's Disorder
A progressive disorder which, to date, has occurred only in girls. Period of normal development and then loss of previously acquired skills, loss of purposeful use of the hands replaced with repetitive hand movements beginning at the age of 1-4 years.
 
Childhood Disintegrative Disorder
Characterized by normal development for at least the first 2 years, significant loss of previously acquired skills. (American Psychiatric Association 1994)
 
Autism is a spectrum disorder. In other words, the symptoms and characteristics of autism can present themselves in a wide variety of combinations, from mild to severe. Although autism is defined by a certain set of behaviors, children and adults can exhibit any combination of the behaviors in any degree of severity. Two children, both with the same diagnosis, can act very differently from one another and have varying skills. Therefore, there is no standard "type" or "typical" person with autism.
 
Parents may hear different terms used to describe children within this spectrum, such as: autistic-like, autistic tendencies, autism spectrum, high-functioning or low-functioning autism, more-abled or less-abled. More important to understand is, whatever the diagnosis, children can learn and function productively and show gains from appropriate education and treatment.
 
The Autism Society of America provides information to serve the needs of all individuals within the spectrum. Diagnostic categories have changed over the years as research progresses and as new editions of the DSM have been issued. For that reason, we will use the term "autism" to refer to the above disorders.