Correlations between olfactory and cognitive functions in early stage Parkinson's disease

Abstract

To explore the general characteristics of olfactory and cognitive functions in early Parkinson's disease (PD) and examine their correlations. The olfactory functions were assessed for 63 PD patients and 55 age and gender-matched normal subjects using T&T olfactory assessment. The scales of mini-mental state examination (MMSE) and Montreal cognitive assessment (MoCA) were employed. The olfactory and cognitive parameters and their relationship were analyzed. There were five different odors in T&T testing liquid and each odor had 5 concentration gradients. The level had an assigned value of 1 to 5 and number 3 represented the standard threshold of olfactory recognition. The mean value of five odors was overall olfactory detection or cognition threshold. (1) The olfactory detection and recognition thresholds were 4.0 ± 1.3/4.8 ± 0.9 in PD group versus 2.5 ± 0.9/2.9 ± 0.9 in normal controls. The scores of MoCA and MMSE were lower in PD group than those in controls (23.7 ± 3.0 vs 25.9 ± 2.0, t = 4.727, P = 0.000; 27.8 ± 1.9 vs 28.9 ± 0.9, t = 4.036, P = 0.000). (2) Linear correlation analysis showed that olfactory recognition threshold was correlated negatively with MoCA scores. The olfactory detection and recognition thresholds were correlated negatively with the score of visual-spatial perception and executive capability (r = -0.365, -0.403, P < 0.05). The olfactory recognition threshold was correlated negatively with the score of delayed memory (r = -0.299, P < 0.05). And this phenomenon was absent in controls. Early PD patients have olfactory dysfunction and cognitive impairment. And these two non-motor symptoms are negatively correlated.