Background and purpose: The aim was to analyze the characteristics and progression of cognitive dysfunction in non-demented idiopathic rapid eye movement sleep behavior disorder (iRBD) patients with baseline olfactory function.
Methods: From a prospective polysomnography-confirmed iRBD cohort, 25 patients (16 patients in 2-year follow-up) and 13 normal controls were included. Initial and 2-year follow-up cognitive functions were analyzed with olfactory function and 18 F-fluorinated-N-3-fluoropropyl-2β-carboxymethoxy-3β-(4-iodophenyl)-nortropane (18 F-FP-CIT) uptake in deep nuclei initially.
Results: Idiopathic RBD patients had impaired attention, memory and executive function compared to controls. Baseline cognitive tests were comparable between the iRBD subgroups with and without hyposmia. 18 F-FP-CIT uptake tended to be lower in the hyposmic group than in the normosmic group. The olfactory test score was positively correlated with amygdala uptake in iRBD patients (P = 0.027). After 2 years, visuospatial and verbal memory dysfunction worsened more in hyposmics than in normosmics. Lower initial olfactory test score was associated with more severe declines in verbal memory function.
Conclusions: Hyposmia may be a predictive sign of cognitive decline in iRBD patients.
Keywords: REM sleep behavior disorder; cohort study; mild cognitive impairment; positron emission tomography.
© European Academy of Neurology 2019.