Significance of hyposmia in isolated REM sleep behavior disorder

Objective To determine if hyposmia in isolated REM sleep behavior disorder (IRBD) predicts short-term conversion to any α-synucleinopathy and declines with time. Methods Olfaction was tested using the University of Pennsylvania Smell Identification Test (UPSIT-40) in 140 consecutive patients with polysomnography-confirmed IRBD and in 77 matched controls. Patients were followed-up during 5.6 ± 3.9 (range 0.2–13) years. Twenty-one patients underwent serial UPSIT-40 evaluations at 1–3 and 4–6 years after baseline. Results UPSIT-40 score was lower in patients than in controls (20.2 ± 6.5 vs. 28.6 ± 5.0; p