Odor Identification Test In REM Sleep Behavior Disorder And Parkinson’s Disease

BACKGROUNDOlfactory dysfunction is one of the non-motor symptoms of Parkinson’s disease (PD), which occurs in at least 90% of cases, and often appears years prior to the motor disturbance. Idiopathic rapid eye movement sleep behaviour disorder (iRBD) is an important risk factor in the development of Parkinson’s disease. It has been considered as a prodromal symptom that may be present before motor symptoms emerge. Longitudinal studies suggested that RBD share the same pathological changes with PD, and most patients with iRBD eventually develop PD or dementia with Lewy Bodies (DLB) after a long period. Since iRBD represent the prodromal phase of PD, the features should be studied in those patients to assist making early diagnosis of PD. Recent studies suggested that hyposmia and other non-motor symptoms of PD can be present in patients with iRBD, however, only few researches compared the olfactory function in the patients with iRBD and in those with PD, and the results were conflicting. To date, there’s no study investigating the olfactory function of Chinese patients with iRBD.OBJECTIVETo investigate the value of olfactory testing in early diagnosis of PD, we assessed the odor identification test in patients with iRBD, patients with PD and healthy controls and analysed features of olfaction dysfunction in patients with pre-motor stage PD.METHODFifty-five Patients with PSG comfirmed idiopathic RBD were recruited from the sleep center. Patients with idiopathic PD who met the United Kingdom PD Society Brain Bank criteria were recruited from the movement disorders clinic. Fifty-five age (+/-five years) and sex-matched subjects with no other neurological abnormalities were selected. Fifty-five age (+/- five years) and sex-matched healthy controls were recruited from the general population in Shanghai. The PD patients and healthy controls had no symptoms or history of RBD. All subjects were excluded from cognitive impairment and other factors that may influence olfactory function. We used 12 odor Sniffin’ Sticks to assess the odor identification. Odor identification scores and accuracies of each odor were compared.RESULTThe median of odor identification scores were 6(5,7) in patients with iRBD,4(3,6) in patients with PD, and 9(8,10) in healthy controls. There was a statistically significant difference in odor identification scores (p< 0.001). The scores of patients with iRBD were significantly lower than controls but higher than those in patients with PD. There were statistically significant differences in odor identification scores between each two groups with Bonferroni correction applied.Compaired with controls, the accuracy of every single odor except cinnamon and pineapple were lower in patients with PD. The accuracy of every single odor except leather, clove, and pineapple were lower than controls in patients with iRBD. The differences between patients with iRBD and controls in accuracy were significant (p< 0.0001) in mint, banana and rose. CONCLUSION Odor identification is impaired in Chinese patients with iRBD and those with PD, and is more impaired in patients with PD than those with iRBD. Compared to controls, odor identification impairment regarding mint, banana, rose, orange, lemon in patients with iRBD is of more significance, which may be more valuable in assisting early diagnosis of PD. On the other hand, the odors of cinnamon and pineapple are not applicable in odor identification test for Chinese population.