The Collaborative International Dictionary of English v.0.48:

Parkinson's \Parkinson's\, Parkinson's disease \Parkinson's
disease\prop. n.
   A disease causing parkinsonism, a degenerative nervous
   disorder; sometimes used loosely as a synonym for
   parkinsonism. More precisely, parkinson's disease is the term
   for the underlying physiological disorder and parkinsonism is
   the term for the set of symptoms associated with the disease.
   See parkinsonism.

   Syn: paralysis agitans, Parkinsonism, Parkinson's disease
        syndrome, shaking palsy.
        [WordNet 1.5]

              Parkinson's disease is the most common form of
              parkinsonism, a group of disorders that are the
              result of the loss of dopamine-producing brain
              cells.                              --Mayo Clinic
                                                  (Report, 1999)
        [PJC]

              According to the National Parkinson's Foundation
              (NPF), 1 million Americans -- including former
              heavyweight boxing champion Muhammad Ali, U.S.
              Attorney General Janet Reno, and television and
              film star Michael J. Fox -- are affected by
              Parkinson's disease.                --Mayo Clinic
                                                  (Report, 1999)
        [PJC]