What is Pervasive Development Disorder (PDD)?
Introduction
Pervasive Developmental Disorder (PDD) is a diagnostic term used to describe a category of five disorders that share impaired functioning in the three domains, or areas, known as the autism “triad”: Communication/Language, Reciprocal Social Interaction, and Restricted and Repetitive. A recent report by Fombonne (2009) provides a prevalence rate of all PDDs together in the 60-70/10,000 range, indicating that PDD is one of the most frequent childhood developmental disorders.
According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; APA 1994) the five PDD categories are:
- Autism Disorder
- Asperger’s Disorder
- Pervasive Developmental Disorder-Not otherwise specified (PD-NOS)
- Rett’s Syndrome
- Childhood Disintegrative Disorder (Heller’s syndrome)
It is important to note that these disorders may not be genetically linked and some may only share behavioural traits. It is therefore critical that disorder-specific strengths and challenges are recognised as early as possible in the preschool years so that educational plans can be developed to accommodate individual strengths and differences.
An excellent informative website is the ACT-NOW resource tool. This site provides fact sheets on the different PDDs and aims to promote understanding of PDDs in the wider community and strategies for working effectively with these children and their families.
In the section below we briefly describe the five disorders that come under the diagnostic term PDD, and briefly highlight the two most common: autism and Asperger’s syndrome.
Autism
Autism is a complex and severe developmental disability with an estimated prevalence of 20 per 10,000 children (Fombonne, 2009). The core characteristics include impairments in social interaction, communication and restricted, repetitive and stereotyped patterns of behaviour. Or more details, please see our autism section.
Asperger’s Syndrome
Asperger’s syndrome is a disorder that can often be confused with autism because of similarities in some behaviours. It has an estimated prevalence of 6 per 10,000 children (Fombonne, 2009). The most defining characteristics of Asperger’s syndrome are a developmental difficulty in social skills and behaviour that contrast with their markedly good language acquisition and intellectual functioning. For more information, please see our Asperger’s section.
Pervasive Developmental Disorder – Not Otherwise Specified (PDD-NOS)
PDD-NOS is a somewhat vague category used to describe a constellation of behaviours that do not necessarily indicate an autism or Asperger’s syndrome diagnosis, perhaps because of later age of onset or because the criteria for any specific PDD have not been met. Also, many professionals incorrectly assume that it means “milder” in all cases (or more like Asperger’s Disorder), and while this is sometimes true, it is not the case for all PDD-NOS cases and so making an assumption that a student diagnosed with PDD-NOS will require fewer modifications at school or that they require fewer services is unwarranted and may disadvantage the student.
Rett’s Syndrome
Rett’s syndrome is rare disorder that affects only girls. Development appears normal during the first 6-18 months and then begins to regress thereafter. Most notable is the loss of fine motor skills which are replaced by repetitive hand wringing movements. These changes are accompanied by additional losses in social engagement, gait or trunk movements, and expressive and receptive language. Problems in communication and social skills, common to all PDDs, are present very early in childhood and their similarity to autism and Childhood Disintegrative Disorder can lead to early misdiagnosis. Informative websites include the International Rett Syndrome Foundation and the Ontario Rett Syndrome Association.
Childhood Disintegrative Disorder (Heller’s Syndrome)
Childhood Disintegrative Disorder is a rare disorder with quite late onset, often over 3 years of age and sometimes up to the age of 10. Children appear to develop normally in the 3-4 years and then gradually begin to lose previously acquired developmental milestones (in the domains of language, motor, and social skills). Unlike Rett’s syndrome that affects only girls, Childhood Disintegrative Disorder can affect both boys and girls. Impairments in language and communication skills strongly resemble that of autism but the onset and pattern of difficulties make this disorder unique.