Olfactory dysfunction and its link with subjective visual vertical (SVV) perception in Parkinson's disease
This source preferred by Ahmed Khattab
Start date: 8 December 2014
Publisher: Digital Olfaction Society, Tokyo Institute of Technology
Place of Publication: Tokyo, Japan
Objectives: Olfactory impairment may precede the onset of motor manifestations in Parkinson's disease (PD) for many years. Recognition of such prodromal phases should guide researchers for more predictive/diagnostic markers for PD. This study aimed to determine the profiles of olfactory dysfunction and subjective visual vertical (SVV) perception in PD patients and compare them to age and gender matched healthy controls. Methodology: This is an open cross-sectional observational study, involving 47 subjects with PD and 47 (age and gender matched) healthy controls. Olfactory function was assessed by the University of Pennsylvania Smell Identification Test. Subjective visual vertical perception was tested using the computerised Rod and Frame test. Mental status was assessed using the Mini-Mental State Examination. Motor function in PD patients was assessed using the motor section of the Unified Parkinson’s Disease Rating Scale part-III (UPDRS-III). Results: There was a statistically significant difference (p< 0.001) between patients and controls in their olfactory functions. PD patients were less likely to correctly identify odours with median score of 6.5/12 compared to 10/12 for controls. The median SVV error for PD group was 0.75° compared to 0.5° for controls (frame was neutral/untilted); this difference was statistically significant (p= 0.02). When the frame was tilted, the median SVV error for PD group was 2.31° compared to 2.00° for controls (not statistically significant). There was no statistical correlation between number of correctly identified odours and an individual’s SVV error. Twelve (25%) PD patients showed evidence of micrographia (small handwriting). Subgroup analysis suggested that PD patients with micrographia (i) have more evidence of olfactory impairment; (ii) reported more SVV errors; (iii) have higher UPDRS-III score in comparison with PD patients with normographia (normal handwriting). These differences were not statistically significant. Correlation studies for the micrographia group revealed weak correlations between (i) SVV and smell test; (ii) SVV and UPDRS-III; (iii) SVV and ability to draw octagons/rectangles. Although these correlations were not statistically significant, no such correlations were found in the normographia group.
Conclusion: PD patients have significant impairment of their olfactory function, however, their ability to estimate visual vertical did not differ significantly from an age and gender matched healthy controls. PD patients with micrographia have more evidence of olfactory impairment, reported more SVV errors, and have more motor problems than patients with normographia. These results were not statistically significant. There is a need to consider introducing digital olfaction technology in assessing patients with PD.