Objective: To determine the relationship of anosmia/hyposmia in Parkinson’s disease (PD) with other motor and non-motor symptoms, and with the degree of nigrostriatal dopaminergic cell loss.

Background: Hyposmia is highly prevalent in PD patients, and may precede the motor symptoms by several years. Previous clinical studies have yielded conflicting results when looking at the association between olfactory function and (non-)motor symptoms.

Method: A total of 295 patients (mean age 65.3 years, disease duration 5.3 years) with a diagnosis of PD were included. Olfactory function was measured using the University of Pennsylvania Smell Identification Test (UPSIT). Motor symptoms were rated using the motor subscale of the Unified Parkinson’s Disease Rating Scale, while using their regular medication. In addition, we used the Mini Mental State Examination as a measure of global cognitive function and validated questionnaires to assess sleep disturbances, psychiatric symptoms, autonomic dysfunction, anxiety and depression. A linear regression model was used to analyze the relationship between UPSIT scores and motor and non-motor variables (for psychiatric symptoms a Poisson regression was performed). In a subgroup of patients (n=155) with a dopamine transporter (DaT) SPECT scan, a similar statistical analysis was performed employing striatal DaT binding.

Results: In total, 82.7% of the patients were either hyposmic or anosmic. In the linear regression model with correction for age, sex, and disease duration, all motor and non-motor symptoms were significantly associated with UPSIT scores [Table 1]. The influence of disease duration on the associations was negligible. In the subgroup of patients with a DaT-SPECT scan, there was a strong association between olfactory test scores and DaT binding in both putamen and caudate nucleus.

Conclusion: The present cross-sectional study demonstrates that olfactory function, as measured by the UPSIT, was related to with various motor and non-motor measures of disease severity in PD patients. This observation emphasizes the profound involvement of the olfactory system in the PD process. In addition, greater olfactory dysfunction was associated with more pronounced loss of nigrostriatal dopamine neurons, as measured by DaT-SPECT, in both the putamen and caudate nucleus. Smell dysfunction may therefore hold promise as a marker of disease progression.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/hyposmia-as-a-marker-of-non-motor-disease-progression-in-parkinsons-disease/