Inclusion Criteria:

• Diagnosis of one of one of the syndromes/diagnoses of interest using established criteria.
• Age ≥ 40 to ≤ 90 inclusive.
• STMS score above 10.
• No active medical disorder that could preclude participation.
• Stable medication regimen over previous four weeks.
• Absence of certain medications that could significantly impact the myocardial 123I-MIBG.
• For those with dementia, caregiver that is with the patient at least four hours/day for at least five days per week.
• For those with dementia , or severe parkinsonism, patient and caregiver willing and able to participate in all study-related procedures.
• Patient is capable of giving informed consent, or if apropriate, has caregiver capable of giving consent on the subject's behalf.

Exclusion Criteria:

• Does not fulfill criteria for any of the desired diagnoses.
• Age > 40 or < 90.
• Women with intact uterus and not post-menopausal unless pregnancy test performed at screening is negative.
• Women who are pregnant or are breast-feeding an infant.
• STMS score < 10.
• Active medical disorder that could preclude participation in this protocol:
  • Hypersensitivity to the radioligand or iodine;
  • Myocardial infarction or cerebral infarct over preceding year, stable or unstable angina, known symptomatic coronary artery disease;
  • Renal disease viewed by the physician to be too severe to warrant myocardial 123I-MIBG scintigraphy imaging;
  • History of significant alcohol or drug abuse;
  • Any other medical disorder considered by the study physicians as inappropriate for enrollment in this protocol.
• Patient or caregiver unwilling or unable to participate in all study-related procedures.
• Caregiver is not with a patient with dementia or severe parkinsonism at least 4 hours/day for at least 5 days/week.
• Patient or caregiver unwilling or unable to provide informed consent.

Eligibility last updated 1/4/22. Questions regarding updates should be directed to the study team contact.