Olfactory deficit in idiopathic rapid eye movements sleep behavior disorder.
BACKGROUND
REM sleep behavior disorder (RBD) is a parasomnia characterized by a loss of atonia and an increased phasic muscle activity during REM sleep. Idiopathic RBD frequently herald an alpha-synucleinopathy, including such as Parkinson's disease (PD) and dementia with Lewy Body (DLB). Pathological changes in the anterior olfactory nucleus and olfactory loss occur very early in the course of PD and DLB. The aim of the study was to assess olfactory function in a large group of idiopathic RBD patients.


METHODS
Fifty-four consecutive polysomnographically-confirmed iRBD patients (44 men, 10 women; mean age: 69.2+/-8.3 years; mean Unified Parkinson's Disease Rating Scale Part III (UPDRS-III) score: 4.9+/-4.3) and 54 age and gender-matched control subjects underwent the Brief University of Pennsylvania Smell Identification Test (B-SIT).


RESULTS
A marked olfactory impairment was observed in the RBD group (mean B-SIT score: 7.1+/-2.5 versus 9.4+/-1.8; p < 0.0001), with 33 (61.1%) RBD patients versus 9 (16.6%) controls showing abnormal olfactory function (p < 0.0001). No correlation was found between the degree of olfactory loss and either duration of RBD symptoms or UPDRS-III score. Deficit in recognize paint thinner odorant showed the highest positive predictive value (0.95) for identifying idiopathic RBD.


CONCLUSIONS
The olfactory deficit found in most idiopathic RBD patients shares similarities with that described in PD and may be a sign of a widespread neurodegenerative process. Its detection may help in identifying subjects at higher risk of developing an alpha-synucleinopathy-mediated neurodegeneration.
Fantini
Maria Livia
ML
Sleep Disorders Center, Department of Neurology, Università Vita-Salute San Raffaele, Via Stamira d'Ancona n. 20, 20127 Milan, Italy. fantini.marialivia@hsr.it
Postuma
Ronald B
RB
Montplaisir
Jacques
J
Ferini-Strambi
Luigi
L
D000368:Aged; D016022:Case-Control Studies; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009460:Neurologic Examination; D000857:Olfaction Disorders / Q000209:etiology*; D010300:Parkinson Disease / Q000150:complications; D020187:REM Sleep Behavior Disorder / Q000150:complications*; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index