"Idiopathic" rapid-eye-movement (REM) sleep behavior disorder is associated with future development of neurodegenerative diseases

OBJECTIVE: To determine whether a diagnosis of idiopathic rapid-eye-movement sleep behavior disorder (RBD) is associated with a future risk of development of neurodegenerative diseases. METHODS: We addressed the objective through development of a structured critically appraised topic that included a clinical scenario, structured question, search strategy, critical appraisal, results, summary of best evidence, commentary, and bottom-line conclusions. Participants included consultant and resident neurologists, clinical epidemiologists, medical librarians, and clinical content experts. RESULTS: A retrospective study of 44 consecutive patients diagnosed with idiopathic RBD demonstrated that 20 patients (45%) developed a neurologic disorder, most commonly Parkinson disease or Lewy body dementia, after a mean of 11.5 years from reported symptom onset and 5.1 years after RBD diagnosis. CONCLUSION: Currently available evidence is limited to cross-sectional and retrospective analyses of patients with RBD. Although ascertainment biases and the retrospective nature of the available evidence limits quantitative analyses, the diagnosis of idiopathic RBD portends a risk of greater than 45% for future development of a clinically defined neurodegenerative disease. This finding has significant implications for clinical neurologic and sleep disorder practice and neurodegenerative disease research.