Incobotulinum Toxin A (Xeomin®) for Troublesome Sialorrhea in Parkinson's Disease (PD)/Parkinsonism

Participants will be recruited if they have Parkinson's disease, Parkinsonism. Inclusion and exclusion criteria are summarized below. Participants will be screened at the first visit to make sure they are eligible for the trial. They will then undergo baseline testing including neurologic evaluation, questions to assess their memory and cognitive status and evaluation of their disease status using parts of the Unified Parkinsons's Disease Ratings Scale (UPDRS) that are routinely used to follow disease progression. They will be given a questionnaire to evaluate the severity of their drooling. Their saliva production will be measured by having them spit into a cup for 5 minutes, twice. At the first visit, after making sure they are eligible for the study and performing the baseline testing and procedures, they will be given either Xeomin or placebo (saline injections without medication) injections in the 4 glands that produce saliva. They will not know which injection they received. This visit will take about 2 hours. They will be followed up every month and asked about side effects, have neurologic evaluation and UPDRS testing and fill-in the questionnaire for drooling severity. Saliva volume will be measured as done at the first visit. At either Month 4 or 5, participants will receive the second injection. This will be a "cross-over" injection, i.e., if they received Xeomin at the first injection they will receive saline at the second and vice versa. Thus, all participants will receive the study medication Xeomin, either as the first injection or the second injection at 4 months or 5 months. The follow up after the second injection will be one monthly visit for 3 months, with similar evaluations as described above. The follow-up visit will take about 1 hour each.