Objective: 1) To assess the determinants of hyposmia on a 5-item smell test. 

2) To assess the agreement between a 5-item smell test and subjective self-assessment of olfaction

Background: Hyposmia is a common feature of Parkinson’s disease (PD) and can be used to predict risk of future PD. Poorer olfaction in men and with age is well documented but other determinants of olfaction in PD are not. A shortened 5-item smell test based on 5-items of the UPSIT (Unified Pennsylvania Smell Identification Test) most predictive of PD has previously been developed by the PREDICT-PD team.

Method: Participants aged 60-80 years old without PD were recruited to PREDICT-PD. 5-item smell test data was collected and participants completed the PREDICT-PD online survey including demographics, family history, lifestyle factors, subjective assessment of olfaction, and questions on non-motor symptoms based on validated questionnaires. Previously published coefficients for each smell test item were used to derive post-test likelihood ratios (LRs) for each participant. Associations of the LRs with survey results were assessed using non-parametric tests. Agreement between subjective and objective olfaction assessment on the 5-item test was assessed using Cohen’s kappa where the  ≤ 15th centile defined hyposmia.

Results: 1808 eligible participants completed the survey and smell test. LRs were positively associated with age (p < 0.001) and male sex (p < 0.001). Higher LRs were associated with an RBDSQ >= 5 when adjusted for age with linear regression (p = 0.005). In males, higher LRs were seen in the presence of erectile dysfunction (p = 0.024). A positive family history for a sibling with PD was positively associated with LRs, even when modelled with age (p =  0.008). Self-assessment of poor olfaction was associated with poor 5-item test performance (p < 0.001) but agreement between methods to identify hyposmia was only fair (Cohen Kappa’s = 0.25). Agreement was slight between smell test performance and self-reported reduced smell (Cohen’s Kappa = 0.17) despite a strong association (p < 0.001).

Conclusion: Our data shows age and sex to determine olfactory performance in a Parkinson’s-specific smell test. RBD and erectile dysfunction were identified as prodromal factors associated with hyposmia. Low agreement between subjective and objective testing strongly supports the use of objective testing to detect hyposmia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/an-objective-shortened-5-item-smell-test-determinants-of-performance-and-agreement-with-subjective-assessment/