Potential early markers of Parkinson disease in idiopathic REM sleep behavior disorder

Background: Idiopathic REM sleep behavior disorder (RBD) is characterized by loss of atonia during REM sleep, resulting in motor activity during dreams. Studies estimate that approximately half of patients with RBD will eventually develop Parkinson disease (PD), so RBD may be an indicator of presymptomatic PD. Several potential early diagnostic markers of PD have been proposed, but they have generally not been tested in presymptomatic PD. The authors hypothesized that these markers may be abnormal in idiopathic RBD. Methods: The authors compared 25 patients with polysomnography-confirmed RBD without PD with age- and sex-matched controls. Color vision, olfaction, quantitative motor testing, and indices of depression, personality, and autonomic function were examined. Results: Patients demonstrated significant impairment in color discrimination and olfactory function. Patients had subtle abnormalities on quantitative testing of motor and gait speed. Autonomic symptoms were more common in patients than controls. Abnormalities were heterogeneous, with some patients scoring normally on all domains, whereas others were severely impaired on multiple domains. Dysfunction on tests of olfactory function, color vision, and motor speed were highly correlated, such that patients who performed poorly on one test tended to perform poorly on the others. Conclusions: Many potential early markers of Parkinson disease are significantly abnormal in idiopathic REM sleep behavior disorder. These abnormalities are present in approximately half of the patients, suggesting a heterogenous pathophysiology.