Self-Reported Versus Objectively Assessed Olfaction and Parkinson's Disease Risk

Background: Poor olfaction is a prodromal symptom of Parkinson's disease (PD); however, self-reported sense of smell is often dismissed as unreliable. Objective: To assess self-reported and objectively assessed sense of smell, independently and jointly, in relation to future risk for PD. Methods: We conducted a prospective analysis using data from 2,424 participants, ages 71-82 at baseline, from the Health, Aging, and Body Composition study. Exposures were self-reported poor sense of smell or taste and the objectively measured 12-item Brief Smell Identification Test score. The outcome was incident PD, analyzed using Cox proportional hazard models adjusted for age, sex, race, and cognitive function. Results: After approximately 10 years of follow-up, both self-reported and objectively tested poor sense of smell were independently associated with a higher risk of developing PD: the hazard ratios (95% confidence interval) were 2.8 (1.3, 5.9) and 4.0 (2.1, 7.5), respectively. When analyzed jointly, compared with participants who reported and tested normal, the hazard ratio was 2.2 (1.0, 4.6) for those reported poor sense of smell but tested normal, 3.6 (1.9, 6.9) for reported normal but tested poor, and 7.8 (3.2, 19.4) for both reported and tested poor. We did not find significant interactions between self-reported and objectively tested sense of smell in predicting PD risk. Conclusion: This study provides preliminary evidence that self-reported poor sense of smell or taste should not be simply dismissed as useless in predicting risk of PD. Future studies should confirm our finding and evaluate whether structured questionnaires may further improve the predictability.