Adrenergic Blockers for Cardiac Changes in Early Parkinson's Disease (Protocol 53136)

REM Behavior Sleep Disorder (RBD) is a sleep disorder causing people to 'act out' their dreams. A high percentage of individuals with idiopathic RBD (iRBD) are known to develop conditions affecting the neurons in the brain such as Parkinson's disease (PD). Based on the increased risk to develop PD, individuals with iRBD are currently considered ideal candidates for therapies that can possibly protects brain cells, due to the critical window of opportunity to intervene early before brain cell loss progresses significantly. Early changes of PD are associated with a number of symptoms including loss of smell, constipation, anxiety and depression. In addition, early heart and brain abnormalities can be visualized using specialized imaging techniques called 123I-MIBG myocardial scintigraphy (MIBG) and dopamine transporter (DAT) single photon emission computerized tomography (SPECT) respectively. The combined presence of certain symptoms and the use of these imaging techniques are considered early markers of PD in individuals with iRBD. In other conditions, like heart failure, MIBG abnormalities are reversed by drugs able to block excessive adrenergic stimulation, known as beta-blockers. In this study the investigators want to learn about the effect of treatment with the beta-blocker carvedilol on MIBG abnormalities found in iRBD patients at risk to develop PD. The investigators believe that reversing the MIBG abnormality might prelude to a slowing of the neurodegenerative process. This drug is approved by the U.S. Food and Drug Administration (FDA) for congestive heart failure, hypertension and left ventricular dysfunction after myocardial infarction. However, carvedilol is not approved by the FDA in patients with iRBD at risk for PD. The available doses for this drug oral formulations are 3.125mg, 6.25mg, 12.5mg and 25mg. Changes visualized with the MIBG imaging technique will be correlated to the presence and severity of neurological (i.e. tremors, stiffness, slow movements, walking difficulties) and other symptoms associated with PD (i.e. abnormal smell, constipation, depression, color vision abnormalities), as measured by specific clinical scales and exams.