Olfactory Identification among Various Subtypes of Parkinson Disease

This study is aimed at investigating the olfactory function among different subtypes of Parkinson disease (PD) and the impact of sex on smell identification test.

In this cross-sectional study, we used Iran-smell identification test (Iran-SIT). PD severity was determined using a Hoehn and Yahr (H&Y) scale. We used analysis of covariance (ANCOVA) to compare the olfactory function among different PD subtypes. All analyses were performed using SPSS software version 16.0.

In total, 66 males and 38 females participated in this study. The most common PD subtype was postural instability and gait difficulty (38.5%). Severe hyposmia and anosmia were found in 44.6 and 19.6% of participants, respectively. Women had a higher score in olfactory function than men (p = 0.44). The score of subjects with stage 1 in the H&Y scale was about 3 points higher than the score with stage 4. The ANCOVA showed a statistically significant effect of subtypes PD on Iran-SIT score after controlling for the effects of covariates (p = 0.03). There is a significant difference between tremor-dominant Parkinson disease (TDPD) and other subtypes of PD (p < 0.05). However, Iran-SIT scores failed to show a significant difference between men and women (p = 0.13).

Our results confirmed that PD is heterogeneous and there is significant variability in odor identification ability in these patients. We observed more olfactory impairment in TDPD, and subjects with higher H&Y stage. We recommended future studies with repeated measurements of different aspects of smell function to characterize the temporal relationship of olfactory dysfunction with PD.