Introduction: 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. Methods: 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. Results: 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). Discussion/Conclusion: 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.

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