Correlations Between Olfactory And Cognitive Functions In Early Stage Parkinson’s Disease

Objective Parkinson’s disease(PD) is a common neurodegenerative disease. And it’s main motor symptoms have been well known. Based on current research progress in this field, the non-motor symptoms of PD patients can appear earlier than the motor symptoms,even exercise greater impact on some people. So scholars become to pay more and more attention to the non-motor symptoms of PD patients. According to recent reports, there is seen to be a link between the non-motor symptoms of PD patients. such as the relationship between olfactory function with sleep disorders, feelings, psychiatric symptoms, even the cognitive function.The objective of our research is to explore the general characteristics of olfactory and cognitive functions in early Parkinson’s disease(PD) and examine their correlations.Methods From May 2013 to August 2014, 63 early stage PD patients in Department of Neurology, the Second Affiliated Hospital of Soochow University were enrolled to this study and 55 age, gender and education matched healthy controls were assessed. The demographic and clinical data was detailedly collected. The scales of mini-mental state examination(MMSE), Montreal cognitive assessment(Mo CA), Hamilton Rating Scale for Depression(HRSD), and Hamilton Anxiety Scale(HAMA) were employed. All subjects should be assessed olfactory functions using T&T olfactory assessment. There were five different odors in T&T testing liquid and each odors 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. Using the test of Homogeneity of Variance and t-test to compare demographic and clinical characteristics in the two groups. Rank-sum test was used to assess detection threshold(DT) and identification threshold(IT). Lastly, we use Spearman’s correlations to analyze the correlations of olfactory functions and clinical characteristics.Results(1) In 63 PD patients, 48 patients had olfactory disorder,account for 76.2%. Accordingly, the quantitative value is 4, account for 10.4% in normal control. There were 5 patients with anosmia in PD patients, but none in normal control. 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. Explaining that early stage PD patients will present with dysosmia.(2) 45 PD patients had cognition disorders,account for 71.4% in all PD patients, while there were 23 subjects in normal control. The scores of Mo CA 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), Futher analysis, the scores of visual-spatial perception and executive capability and delayed memory were also lower in PD group than those in controls(3.3±1.4 vs 4.2±1.0, t=3.963, P=0.000, 2.0±1.5 vs 2.8±1.0, t=3.770, P=0.000). So, it proves that early stage PD patients have cognitive impairment, mainly shows in two aspects:visual-spatial perception and executive capability and delayed memory.(3) The 63 PD patients were divided into two parts: 48 dysosmic PD patients(PD-D group) and 15 osmatic PD patients(PD-O group). The scores of Mo CA, visual-spatial perception and executive capability and delayed memory were lower in PD-D group than those in PD-O group(23.2±3.0 vs 25.3±2.5, 3.0±1.4 vs 4.2±0.9, 1.8±1.5 vs 2.7±1.4,P < 0.05). Similarly, divide PD patients group with cognitive function into two parts:the group of PD patients with cognitive disorders(PD-C group) and the group of PD patients with normal cognitive function(PD-N group). The scores of IT and DT in PD-C group were all higher than those in PD-N group, but they did not achieve statistical significance.(4) Linear correlation analysis showed that olfactory recognition threshold was correlated negatively with Mo CA scores(r=-0.385, P<0.05). 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). All this phenomenon was absent in controls.Conclusion Early PD patients have olfactory dysfunction and cognitive impairment. The damage of cognitive function mainly embodied in the visual-spatial perception and executive capability and delayed memory. What calls for special attention is that olfactory and cognitive function are negatively correlated.