Abstract
The 40-item University of Pennsylvania Smell Identification Test (UPSIT) is an effective instrument to detect olfactory dusfunction in Parkinson’s disease (PD). It is not clear, however, whether tests of this length are necessary to detect such dysfunction. Several studies have suggested that detection of certain odors is selectively compromised in PD, and that a test comprised of these odors could be shorter and more specific for this purpose. Therefore, we attempted to identify a subset of UPSIT odors that distinguish PD from controls with similar or improved test characteristics compared to the full test. The discriminatory power of each odor was examined using UPSIT data from a discovery cohort of 314 PD patients and 314 matched controls and ranked using multiple methods (including odds ratios, regression coefficients and discriminant analysis). To validate optimally discriminant subsets, we calculated test characteristics using data from two independent cohorts (totaling 306 PD and 343 controls). In the discovery cohort, multiple novel 12-item subsets (and the previously described Brief Smell Identification Test-B) performed similarly or improved upon the UPSIT and were better than 12 random items. However, in validation studies from independent cohorts, multiple subsets retained test characteristics similar to the full UPSIT, but did not outperform 12 random items. Differential discriminatory power of individual items is not conserved across independent cohorts arguing against selective hyposmia in PD. However, multiple 12-item subsets performed as well as the full UPSIT. These subsets could form the basis for shorter olfactory tests in the clinical evaluation of Parkinsonism.
Highlights
Olfactory impairment is a common finding in Parkinson’s disease (PD), with estimates of prevalence ranging from 50% to more than 90%.1–6 Neurons of the olfactory system are among the first to display PD-related Lewy pathology and clinical anosmia or hyposmia may be detected years before motor symptoms present, suggesting that olfactory impairment may be one of the earliest manifestations of synucleinopathy.[7,8,9] Whether or not such pathology causes olfactory dysfunction is unknown, as other explanations for the early deficits are possible.[10]
“PD-specific” subscales derived in one population do not retain discriminatory power across independent cohorts We examined the performance of our putative PD-specific subsets with individual item University of Pennsylvania Smell Identification Test (UPSIT) data from two independently derived validation cohorts
As age and sex are important determinants of olfactory function, we examined the test characteristics of the UPSIT, B-SIT-B and 12 UPSIT items (“Combined” list) we defined as most highly discriminatory in the discovery cohort (Table 5) as a function of age and sex using data from all three cohorts (N = 1279)
Summary
Olfactory impairment is a common finding in Parkinson’s disease (PD), with estimates of prevalence ranging from 50% to more than 90%.1–6 Neurons of the olfactory system are among the first to display PD-related Lewy pathology and clinical anosmia or hyposmia may be detected years before motor symptoms present, suggesting that olfactory impairment may be one of the earliest manifestations of synucleinopathy.[7,8,9] Whether or not such pathology causes olfactory dysfunction is unknown, as other explanations for the early deficits are possible.[10]. Numerous tests have been used to measure olfactory function in PD with odor identification tests being the most common.[12,13,14,15] Among the best-characterized and robust of such tests is the University of Pennsylvania Smell Identification Test (UPSIT).[16] The UPSIT is comprised of four booklets, each of which contains 10 pages. The UPSIT is a robust measure of olfactory dysfunction in PD and has been described in numerous studies.[17] use of the UPSIT (and other well-characterized methods such as “Sniffin Sticks”18) can be limited by difficulty of incorporating such a test into routine clinical encounter. Shorter tests would seem to be preferable both from the perspective of the patient and the neurologist, within a busy clinical setting
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