Currently, there is no clear diagnostic test that can be used to confirm the diagnosis of Parkinson's disease, or a biomarker that can track its progression. Patients with Parkinson's have many abnormalities of the autonomic nervous system, which may be related to Parkinson's changes outside of the brain. A new device called the SudoScan, which measures autonomic sweating changes, may be a simple way to test for autonomic changes in Parkinson's.

The investigator plan to see whether SudoScan can identify Parkinson's disease and whether SudoScan abnormalities might be present even in early (prodromal) Parkinson's stages.

The investigator will assess SudoScan in a group of Parkinson's patients, normal healthy controls, patients with non-Parkinson's neurodegeneration, and patients with REM sleep behavior disorder (an early/prodromal Parkinson's state). Abnormalities will be correlated with standard autonomic tests and with skin biopsy findings Parkinson's degeneration in the peripheral autonomic fibers.

If the investigator can find a reliable way to diagnose and follow Parkinson's disease, he will be able to correctly identify Parkinson's (even in its earliest stages). This will improve the chance to find protective treatments against Parkinson's, by preventing false diagnosis and by providing a new marker to track disease progression.

If successful, the investigator will aim to validate the findings on a large sample of Parkinson's and also to track changes over time in the original cohorts

Inclusion Criteria:

1. PD patients: All will meet criteria for probable PD, according to the new MDS Clinical Diagnostic criteria
2. Non-PD parkinsonism patients: They will have with progressive supranuclear palsy, multiple system atrophy, 'vascular parkinsonism' or corticobasal syndrome. All patients will have parkinsonism according to UK brain bank criteria, with a diagnosis of one of the above conditions made according to gold-standard expert evaluation. No patient will meet MDS Criteria for probable PD.
3. iRBD patients: All patients will have polysomnogram-confirmed RBD according to American Academy of Sleep Medicine Criteria. Patients will be free of parkinsonism and dementia according to neurological examination and will have no untreated sleep apnea, epilepsy, or other abnormalities that could cause dream enactment behavior.
4. Controls: These will be age matched (within 5 years) and sex-matched (with >90% concordance). All controls will have an examination confirming the absence of parkinsonism, and will have no symptoms of REM sleep behavior disorder, as assessed with the RBD1Q and expert interview.

Exclusion Criteria:

1. Diabetes Mellitus - In addition to causing autonomic neuropathy, hyperglycemia itself is known to interfere with results of the sudomotor scan
2. Any preceding diagnosis of autonomic neuropathy (of a cause other than PD)
3. Dementia of severity sufficient to preclude informed consent, MoCA <23.
4. Prescription of medications that directly alter peripheral autonomic function, including beta-blockers, sympatholytics (i.e. clonidine) and non-specific alpha-blockers.

De-identified clinical data will be shared with the Michael J. Fox Foundation (the study funder) for Parkinson's research. These data may be kept for storage at a central repository either hosted by the Michael J. Fox Foundation, its collaborators, or consultants and will be kept indefinitely. In order to advance scientific discoveries, your de-identified data will be made publically available (with no personal identifying information) for the intended use of research in Parkinson's disease as well as other biomedical research studies that may not be related to Parkinson's disease.