Objective: To explore the general characteristics of olfactory and cognitive functions in early Parkinson's disease (PD) and examine their correlations.
Methods: 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.
Results: (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.
Conclusion: Early PD patients have olfactory dysfunction and cognitive impairment. And these two non-motor symptoms are negatively correlated.