Understanding PDD and PDD-NOS

Pervasive Developmental Disorder (PDD) is the category containing autism, Asperger Syndrome, Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS), Childhood Disintegrative Disorder, and Rett Syndrome. PDD-NOS is a catchall diagnosis for people having most but not all the characteristics of autism. People with these disorders are often described as “autistic-like” or developmentally delayed with autism symptoms; recently, experts have put them on the autism spectrum.
Although classified under the Pervasive Developmental Disorders, Rett Syndrome has identifiable physical differences such as reduced muscle tone (causing the child to seem “floppy”) and stereotyped hand movements such as wringing or waving. Additionally, Rett Syndrome produces an identifiable chromosomal difference.
People with PDD-NOS need some special services but don’t fit the behavioral criteria for any of the other categories of autism. Maybe the person lacks meaningful speech or has stereotypical movements such as hand flapping or rocking, but he or she doesn’t have enough of the symptoms to fill the symptom bucket and be considered autistic. This lack of a label may make it tougher to get services, because the autism label — although considered stigmatizing by some people — does generally get you educational services in most places.
Because autism is a spectrum disorder without a clear dividing line, some people fall just on the other side of the line — they don’t qualify for autism disorder because of late onset of symptoms, or they don’t have enough behavioral symptoms. However, their disorder significantly impacts daily functioning on a regular basis.