This investigator-initiated study is meant to determine whether a correlation exists between cardiac denervation (as assessed by 123I-mIBG scans) and subjective ratings of fatigue in patients with Parkinson disease. Subjects will be recruited from the Movement Disorder section of the department of Neurology. Subjects fulfilling inclusion/exclusion criteria will undergo testing to exclude confounding factors such as depression or sleep dysfunction. Subjects will also complete several validated measures of fatigue. These measures will be correlated to a calculated ratio obtained from an 123I-mIBG scan to provide an indication of the relative denervation present in the subject. These findings will serve as pilot data for a larger prospective study exploring this topic.