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Unawareness of hyposmia in patients with idiopathic Parkinson’s disease

BACKGROUND: Loss of olfaction is a hallmark of neurodegenerative disorders such as idiopathic Parkinson’s disease (PD) and it may precede the clinical syndrome of PD by many years. Olfactory bulb is probably the earliest site of pathology in PD. This study examines the frequency of unawareness of hyposmia in study cohorts with and without PD and its correlation with cognitive impairment. The objective of this study was to assess olfactory function using the Indian Smell Identification Test (INSIT), which evaluates the unawareness of hyposmia in patients with idiopathic PD. MATERIALS AND METHODS: Olfaction was assessed in 30 PD patients and 30 healthy controls by using INSIT. During this test, the subjects were asked to identify smell from a set of choices and were scored out of 10. The cutoff used for hyposmia was an INSIT score of ≤4. Unawareness was defined as reporting a normal sense of smell in the setting of a low INSIT. Cognitive status was assessed by using Mini Mental State Examination (MMSE) to study the effect of cognitive status on unawareness of hyposmia in PD cases. RESULTS: The mean age for the PD and control groups was 64.3± 10.6 years and 63.9 ± 10.2 years, respectively. Most of the participants were males: 53% and 56% in the PD and control groups, respectively. Out of the 30 patients in each group, 18 patients were unaware of hyposmia in the PD group as compared with 4 patients in the control group. The mean smell identification score using INSIT was 4.13 ± 2.42 in the PD group and 6.86 ± 2.3 in the control group, which was found to be significant with a p value of <0.0001. In the PD group, the mean MMSE score in subjects who were unaware of hyposmia was 27.89, whereas the mean MMSE score in subjects who were aware of smell was 29.25. This was found to be not statistically significant with a p value of 0.1087. CONCLUSION: Unawareness of hyposmia in patients with PD is high as compared with that in the elderly without PD. Under-reporting of hyposmia is seen in patients with PD. There is no increase in the unawareness of hyposmia in patients with PD who exhibit dementia. All these lead to a premise whereby population screening using INSIT could be used for the early detection of PD in those who already harbor the earliest pathology of neurodegeneration.