Helpguide.org. Provides an overview of Parkinson’s Disease, a progressive disorder of the central nervous system that affects more than 1.5 million people in the United States, and is most common in people over 60. Includes a good summary of the primary and secondary symptoms of parkinson’s, it’s diagnosis and treatment (there is no cure), and tips for living with parkinson’s. Also discusses the relationship between parkinson’s and dementia; over 20% of people with parkinson’s also develop dementia. The symptoms can be similar, so parkinson’s and dementia are sometimes difficult to distinguish.