Optimizing odor identification testing as quick and accurate diagnostic tool for Parkinson's disease

Area of Science:

• Neurology
• Olfactory Neuroscience

Background:

• Parkinson's disease (PD) diagnosis can be challenging, especially in early stages.
• Objective diagnostic tools are needed to complement clinical assessments.

Purpose of the Study:

• To evaluate odor identification testing as a rapid, cost-effective, and dependable method for diagnosing PD.
• To determine the diagnostic accuracy of the Sniffin' Sticks 16-item (SS-16) test and a reduced odor set (SS-8) in distinguishing PD patients from controls and other neurological conditions.

Main Methods:

• The Sniffin' Sticks 16-item (SS-16) test was administered to 646 PD patients, 606 controls, 75 patients with atypical parkinsonism or essential tremor, and 24 patients with idiopathic REM sleep behavior disorder across three European centers.
• A discovery cohort was used to identify the most discriminative odor subset (SS-8) for PD using L1-regularized logistic regression.
• Diagnostic accuracy was validated in separate patient and control groups.

Main Results:

• PD patients exhibited significantly lower olfactory performance compared to controls and non-PD patients (P < 0.001).
• Both the full SS-16 and the SS-8 demonstrated excellent discrimination for PD (AUC ≥ 0.90 for controls, AUC ≥ 0.91 for non-PD patients).
• The SS-8 correctly identified all 8 incident PD cases in the idiopathic REM sleep behavior disorder cohort (sensitivity 100%).

Conclusions:

• Odor identification testing, particularly with a validated subset of eight odors, offers high diagnostic accuracy for differentiating PD from controls and mimics.
• The SS-8 serves as a practical tool for the initial evaluation of parkinsonism and for indicating PD risk.