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PDD and ASD
If you’ve ever known anyone with a diagnosis of autism, you’ve probably heard of PDD and wondered, what are pervasive developmental disorders? In the current mental health diagnostic manual, the DSM IV, published by the American Psychiatric Society, PDDs include:
- Autistic disorder,
- Asperger syndrome,
- Pervasive developmental disorder-not otherwise specified (PDD-NOS),
- Childhood disintegrative disorder
- Rett syndrome
Terminology can be a bit confusing as pervasive developmental disorder and autism spectrum disorder (ASD) are at times used interchangeably in the literature. Both terms may be used to refer to all five categories, while sometimes ASD only encompasses the first three. Pervasive developmental disorders as an umbrella term may be further confused with the specific label PDD-NOS.
Proposed changes to the DSM-V, expected to be published in 2013, will help to clarify the diagnoses by eliminating Rett syndrome whose symptoms differ significantly, and combining the others under one heading of autism spectrum disorders. Diagnostic criteria will be streamlined to make diagnoses along the spectrum more reliable.
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Pervasive developmental disorders are neurological in nature, and are present at birth. Parents are usually the first to notice symptoms and many children receive a diagnosis as infants or toddlers. Some children may be diagnosed later as they begin to struggle with communication and social demands. Since there are no standard medical tests for PDDs, pediatricians, psychiatrists, psychologists or other members of a diagnostic team, rely on direct observation and information provided by family, school staff and/or others who spend time with the individual in question. Observation and interview tools such as the Autism Diagnosis Interview-Revised (ADI-R), the Autism Diagnostic Observation Schedule (ADOS-G) and the Childhood Autism Rating Scale (CARS) may be used.
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In order to receive a diagnosis of pervasive developmental disorder a person must exhibit symptoms in three main areas, though symptoms vary greatly in presentation and severity from one individual to the next. Examples of possible symptoms may include:
Impairments in Language and Communication
- Delayed speech (except in Asperger syndrome)
- Poor eye contact
- Poor understanding of body language, gestures and facial expression
- Literal understanding of language
Impairments in Social Interaction
- Difficulty taking turns
- Inappropriate use of toys
- Inability to take another perspective
- Difficulty regulating emotions
Restrictive and Repetitive Patterns of Behavior
- Difficulty with transitions
- Preference for order and structure
- Intense preoccupations with particular topics or objects
- Repetitive physical behaviors such as rocking or flapping
Some individuals with PDDs may also experience seizures or sensory issues, manifesting as over or under-sensitivity to light, sound, texture, taste or smell. Others may have delayed cognitive abilities.
Child disintegrative disorder (CDD) and Rett syndrome are rare, compared to the other PDDs and additional symptoms may be present in children with these disorders. For example, girls with Rett syndrome may lose previously developed skills and begin repeatedly wringing their hands while children with CDD may lose bladder and bowel control.
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What are pervasive developmental disorders’ main origins? A definitive cause, in the area of autism, remains elusive but there is a great deal of international research happening to narrow down the possibilities. Several areas are being investigated and multiple causes are possible.
- Neurobiological - Brain imaging techniques such as MRI and PET scans are allowing researches to study brain structures (e.g. cerebral cortex, cerebellum, brain stem) and brain functions as they relate autism spectrum disorders. One area of study is focusing on the enlarged brain structure sometimes found in individuals with autism and posits accelerated brain growth in the early months of a child’s life. Other research is looking at how neurotransmitters travel from cell to cell within the brain.
- Genetic factors – Researchers believe there is a genetic basis for autism spectrum disorders stemming from abnormal development in chromosomes that are inherited. Twin studies and family histories are providing evidence to support these ideas.
- Other Causes - Other possibilities implicated in the development of pervasive developmental disorder are food allergies, an overabundance of yeast in the digestive system and environmental toxins though research has not yet turned up adequate scientific evidence in these categories.
An issue of great controversy in the field of autism, has been the possible link between vaccinations and pervasive developmental disorders. In a study published in 1998, Dr. Andrew Wakefield and colleagues claimed to find evidence of a link between the MMR vaccination and autism. Newer research denies the evidence of such a link and the original study has been retracted by the medical journal where it was originally published, due to inaccurate research methodologies. Plotkin, Gerber and Offit (2009) published a review of over 20 studies refuting the link between autism and vaccinations, concluding that children who had been immunized were no more likely to end up with a PDD diagnosis than those who were.
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National Institute of Neurological Disorders and Stroke, http://www.ninds.nih.gov/disorders/pdd/pdd.htm
National Institute of Mental Health, http://www.nimh.nih.gov/health/publications/autism/complete-index.shtml
Kid’s Health: Autism and Pervasive Developmental Disorders, http://kidshealth.org/parent/medical/learning/pervasive_develop_disorders.html
American Psychiatric Association DSM-5 Development, www.dsm5.org
Plotkin, S., Gerber, J.S., and Offit, P.A. (2009). Vaccines and Autism: A Tale of Shifting Hypothesis, Clinical and Infectious Diseases, 48, 456-461. http://cid.oxfordjournals.org/content/48/4/456.full