Predictive value of abbreviated olfactory tests in prodromal Parkinson disease

There is disagreement in the literature whether olfaction may show specific impairments in Parkinson Disease (PD) and if olfactory tests comprised of selected odors could be more specific for diagnosis. We sought to validate previously proposed subsets of the University of Pennsylvania Smell Identification Test (UPSIT) odors for predicting conversion to PD in an independent, prodromal cohort. Conversion to PD was assessed in 229 participants in the Parkinson At Risk Study who completed baseline olfactory testing with the UPSIT and up to 12 years of clinical and imaging evaluations. No commercially available or proposed subset performed better than the full 40-item UPSIT. The proposed PD-specific subsets also did not perform better than expected by chance. We did not find evidence for selective olfactory impairment in Parkinson disease. Shorter odor identification tests, including commercially available 10-12 item tests, may have utility for ease of use and cost, but not for superior predictive value.

Automated summary

There is disagreement regarding whether olfaction may show specific impairments in Parkinson Disease (PD) and if specific odor tests could be more effective for diagnosis. This study aimed to validate previously proposed subsets of the University of Pennsylvania Smell Identification Test (UPSIT) odors for predicting conversion to PD. The results showed that no subsets, including proposed PD-specific ones, performed better than the full 40-item UPSIT. Therefore, selective olfactory impairment in Parkinson disease was not found.