There are 5 stages that range from minor to severe.
"Stage 1-symptoms are only on one side of the body
Stage 2-symptoms are on both sides of the body, but balance isn't impaired
Stage 3-there is some balance impairment and disability
Stage 4-disability is severe, but the person can still walk or stand without help
Stage 5-the person cannot stand or walk, and is wheelchair-bound or bedridden" -
health.howstuffworks.comIn the more severe stages, patients "develop a shuffling walk, muffled speech, small and illegible handwriting, emotional changes, including depression, a blank stare, and difficulty chewing and swallowing."
The disease is different for every person. These stages can either slowly progress from stages 1-5 for years, or quickly go from one stage to the next relatively quickly.