Parkinson's disease is a progressive, neurological disorder, which is treated mainly with drug therapy. It occurs when cells in the brain that control movement are lost. These cells produce dopamine, a chemical messenger, that enables people to perform smooth, co-ordinated movements. For a full explanation of the Dopamine Theory try here or here [use your Back button to return].
Once 80% of these cells have been destroyed, the symptoms of Parkinson's will appear. Symptoms include shaking, muscle stiffness, fatigue and slowness of movement. Parkinson's can therefore affect all daily activities, including talking, walking, swallowing and writing.
At present there is no cure for Parkinson's, but there is a range of treatments available to help control the symptoms and maintain quality of life. These include drugs, physiotherapy, speech and language therapy, occupational therapy and surgery.
In the long-term, however, drug treatment can result in severe side-effects, including abnormal jerking movements (called dyskinesia), confusion, and fluctuations in the ability to perform movements. There is a Dyskinesia Self Evauluation Form here.
The UK Society's website has a lot of helpful information here (choose Living with Parkinsons from the left hand menu).