The relationship between clinical severity and olfactory bulb volume in idiopathic parkinson's disease

Idiopathic Parkinson's disease (IPD) is a clinical condition in which derangement of motor function occurs due to degeneration of the basal ganglia (BG), as part of a neurodegenerative process. The sense of smell is lost years before the occurrence of motor symptoms of IPD. The presence of atrophy of the olfactory bulb was shown in patients with loss of the sense of smell in many studies. Magnetic resonance imaging (MRI) is a reliable modality in measurement of the volume of olfactory bulb (OBV). We aimed to investigate a correlation between the clinical severity of IPD and OBV in this study. Thirty six patients admitted at the Department of Neurology of Gaziantep University Medical School and diagnosed as having IPD based on history, neurological examination and imaging studies, who accepted to participate in this study, and 23 age-matched controls without a history of IPD or any disorders that may cause OB atrophy were included in this study. The right, left and total OBV values of these two groups were compared. The patient group was divided in 3 subgroups according to Hoehn – Yahr stages, and the Unified Parkinson's Disease Rating Scale (UPDRS) scores of the patient group were also calculated. The right, left and total OBV values of the patient group were lower than the controls (p=0,000). There were no significant differences between patient subgroups according to Hoehn-Yahr staging, in terms of right, left and total OBV values of the IPD group (p>0.05). A significant negative association was detected in the IPD group, between the total OBV values and UPDRS scores (p=0,036). A statistically significant association could not be found between age and total OBV value in both the IPD group and controls (p>0.05). When the individuals in the IPD and control groups were stratified according to age, a significant association could not be found between total OBV values and age in both the IPD group and controls (p>0.05). In conclusion, the loss of sense of smell that occurs in the early phases of IPD and the ensuing OB atrophy increase in correlation with the UPDRS score. A reason of not being able to show this correlation with Hoehn-Yahr staging may be related with Hoehn-Yahr staging evaluating only the motor functions of the patients. Although our study may be significant in showing that OBV measurement may be used in evaluating the clinical severity of IPD, further studies with larger sample sizes are required.