Idiopathic hyposmia as a marker of prodromal Parkinson's disease - a cohort study.
Level 3 - non-randomized controlled study
Cross-sectional analysis within an established observational cohort (PREDICT-PD)
PubMed 41219349 · doi:10.1038/s41598-025-23293-4
What was done
Evaluated the validity of a shortened 5-item objective smell test in 1,472 participants aged >60 years without Parkinson's disease (PD) enrolled in the PREDICT-PD cohort. Participants completed the smell test alongside an online evaluation battery consisting of subjective olfaction assessment, the REM Sleep Behaviour Disorder Single-Question Screen (RBD1Q), UPDRS Part II (subjective motor symptoms), and the BRadykinesia Akinesia INcoordination (BRAIN) tapping test. PD log odds derived from the smell test were analyzed against clinical and demographic features using non-parametric tests.
What was found
The abstract reports no exact numerical values, correlation coefficients, or p-values. It reports that objective smell performance worsened with advancing age and was lower in males. PD log odds calculated from the 5-item smell test correlated with positive RBD screening and objective bradykinesia on the BRAIN tap test, but not with UPDRS Part II subjective motor scores. Subjective smell assessments showed only fair agreement and weak correlation with objective smell testing, and subjective smell did not correlate with motor function.
Why it matters
Supports the utility of a brief 5-item objective olfactory test for scalable prodromal PD risk stratification, demonstrating that subjective self-reporting of olfaction fails to capture subclinical motor dysfunction detected by objective testing.
Limits
The abstract provides no quantitative metrics (e.g., sensitivity, specificity, AUC, or exact correlation statistics). The study design is cross-sectional without reported prospective conversion to clinical PD. Assessments relied on remote, self-administered online tools and tap tests which may introduce variability compared to in-person clinical examinations.
Cited by
- supports Loss of smell is one of the earliest features of Parkinson's and Alzheimer's disease, preceding memory loss and tremor by years or decades.