Olfactory function deteriorates in patients with Parkinson's disease complicated with REM sleep behavior disorder

Introduction It is not concluded whether the association between olfactory dysfunction and REM sleep behavior disorder (RBD) were worsen cognitive function in patients with Parkinson's disease (PD). We sought to evaluate the impact of these symptoms in PD. Methods We examined 62 patients with PD using an olfactory test (Odor Stick Identification Test for Japanese: OSIT-J) and polysomnography (PSG). We divided the patients into 3 groups: PD with clinical RBD (n = 32), PD with subclinical RBD (n = 11), and PD with normal REM sleep (n = 19). We compared their clinical backgrounds, results of OSIT-J, autonomic functions, and cognitive functions such as Montreal cognitive assessment Japanese version (MoCA-J). Some factors associated with RBD were analyzed by multiple regression. Results There were significant differences in the results of OSIT-J, and autonomic and cognitive functions between the 3 groups. There were significant differences in the total OSIT-J score between the 3 groups (PD with clinical RBD: 3.3 ± 2.2, PD with subclinical RBD: 4.0 ± 2.6, PD with normal REM sleep: 6.7 ± 3.0, p
Highlights • Patients with Parkinson's disease (PD) and REM sleep behavior disorder (RBD) had severe olfactory deficits. • Olfactory function is associated with RBD in patients with PD. • Olfactory dysfunction might be important in the development of PD.