Odor-Specific Symptoms in Parkinson's Disease-UPSIT-TC Odor Identification Status Versus Clinical Severity

Olfactory dysfunction is a well-recognized prodromal sign of Parkinson's disease (PD). This study aimed to explore the potential of short-form olfactory tests as a more convenient method for assessing PD symptoms in clinical practice. This retrospective cross-sectional study included 176 patients with PD. For each clinical measure, 40 separate logistic regression models evaluated its association with correct identification of each UPSIT-TC odor. Odors showing nominal associations at unrounded p < 0.05 were designated candidate symptom-associated odors. A symptom-specific odor score was constructed when at least two odors (≥ 2) met this criterion. Associations of each clinical measure with the UPSIT-TC total score and its corresponding symptom-specific odor score were subsequently evaluated using correlation analyses and covariate-adjusted regression models. Across all clinical measures, 101 nominal odor-clinical associations involving 31 unique odors were identified, with 17 clinical measures meeting the ≥ 2-odor criterion. Symptom-specific odor scores generally showed stronger unadjusted correlations with their corresponding clinical measures than did the UPSIT-TC total score. After adjustment for age, sex, disease duration, and levodopa equivalent daily dose (LEDD), with false discovery rate correction across 32 models, symptom-specific odor scores remained significantly associated with MDS-UPDRS total and Parts I-III scores, bradykinesia, rigidity, axial symptoms, NMSS total and gastrointestinal and urinary domain scores, MoCA scores, and NPI total scores. In contrast, the UPSIT-TC total score remained significantly associated only with rigidity. Symptom-specific odor scores have the potential to serve as a more clinically practical tool for assessing PD symptom burden than the UPSIT-TC total score. Further large-scale, multicenter studies are needed to explore odors with higher specificity for PD clinical symptoms.