There are so many syndromes out there with Parkinson-like symptoms, or parkinsonism, that getting an accurate diagnosis can take years. Parkinsonism is any group of neurological disorders that have symptoms similar to PD - tremor, muscle rigidity, hypokinesia. Among those are Multiple System Atrophy (MSA), sometimes referred to as Shy-Drager syndrome. The National Institutes of Health recently published literature based on a study that shows autonomic assessments do not differentiate between PD, MSA, and PSP (progressive supranuclear palsy).
Keith's brother has MSA but was originally diagnosed with PD. He and his family went through hell to get an accurate diagnosis, but even now most people, including some doctors, want to lump his condition in with PD. Part of MSA is parkinsonism, and much of the treatments are the same, however, the two are different illnesses and should be referred to as such. At a later date I will post an interview with his wife, but for now, here are some interesting links regarding MSA -
The National Institutes of Health's literature regarding autonomic assessments