The characteristic slowness of movement and tremors that are characteristic of Parkinson’s disease (PD) often appear asymmetrically in patients. A new model of PD, published in the
Symptoms and the speed with which they progress vary greatly among patients. In many patients, motor symptoms initially appear in one side of the body. Some patients develop constipation, loss of smell, sleep disorders, and other symptoms several years before diagnosis, but others do not.
Although it is possible to define several subtypes of PD characterized by similar constellations of symptoms, the underlying causes of these differences are poorly understood. Aggregation and neuron-to-neuron spread of the protein alpha-synuclein is thought to be involved.