Abstract
BackgroundOlfactory dysfunction is common in Parkinson's disease (PD) and idiopathic rapid eye movement sleep behavior disorder (iRBD), which is a risk factor in the development of PD. However, a few studies have conflicting results when comparing dysosmia in the patients with iRBD and PD. There is no study investigating the olfactory function in Chinese patients with iRBD. Additionally, the Sniffin’ Sticks screening 12 test (SS-12) contains several odors that are not familiar to people in different cultures.MethodsOdor identification was evaluated in iRBD patients (n = 54), PD patients (n = 54) and healthy controls (n = 54). With the identification data, a brief odor identification test was established and then validated in other subjects.ResultsOdor identification scores in iRBD patients were significantly higher than those in PD patients (P<0.001) but lower than those in controls (P<0.001). At the cut-off value of 7.5, the Sniffin’ Sticks clearly differentiated iRBD and PD patients from the controls, and the brief test could increase the specificity in diagnosing PD. Neither the Sniffin’ Sticks nor the brief test could clearly differentiate PD and iRBD patients from each other.ConclusionsOlfaction is more impaired in PD patients than in iRBD patients, possibly due to the heterogeneity of iRBD patients. The Sniffin’ Sticks could be a useful tool for differentiating iRBD patients from the healthy population, and it could be useful for screening people at high-risk of PD in China, especially when combined with polysomnography. To reduce the expense and time required for the Sniffin’ Sticks test, this study shows that a brief test is feasible.
Highlights
Parkinson disease (PD), clinically characterized by tremor, bradykinesia, rigidity and postural instability, is a multisystem disease with variegated non-motor (NM) deficits, including impaired olfaction, sleep disorders and neuropsychiatric disorders [1]
At the cut-off value of 7.5, the Sniffin’ Sticks clearly differentiated idiopathic rapid eye movement sleep behavior disorder (iRBD) and Parkinson's disease (PD) patients from the controls, and the brief test could increase the specificity in diagnosing PD
Olfaction is more impaired in PD patients than in iRBD patients, possibly due to the heterogeneity of iRBD patients
Summary
Parkinson disease (PD), clinically characterized by tremor, bradykinesia, rigidity and postural instability, is a multisystem disease with variegated non-motor (NM) deficits, including impaired olfaction, sleep disorders and neuropsychiatric disorders [1]. Rapid eye movements sleep behavior disorder (RBD) is a parasomnia characterized by the intermittent loss of REM sleep electromyographic (EMG) atonia and dream-enacting behavior [5, 6]. It is one of the non-motor symptoms (NMS) of PD that may precede the onset of motor symptoms of PD patients [7]. Studies have reported that RBD occurs in approximately 30–60% of patients with PD [8], and 50–90% of idiopathic RBD (iRBD) patients eventually developed PD or dementia with Lewy Bodies (DLB), or other synucleinopathies [9,10,11], indicating that a considerable proportion of iRBD patients are in the prodromal phase of PD. The Sniffin’ Sticks screening 12 test (SS-12) contains several odors that are not familiar to people in different cultures
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