Objective: To investigate the relationship between impairments of the cardinal motor symptoms and odor identification deficits in Parkinson’s disease (PD).

Background: Although hyposmia has been shown to correlate with striatal dopaminergic losses in PD, previous studies have shown no or limited motor correlates with hyposmia. The variable and limited association between these variables may be explained by specific rather than global motor correlates of hyposmia.

Methods: PD patients, n=151 (F39; 65.9±7.7 (50-86) years old; 6.1±4.4 (0.5-20) years motor disease duration, HY range 1-5, and mean MOCA score 25.9±2.6 (15-30) underwent clinical testing. Olfactory function was assessed using the 40-item University of Pennsylvania Smell Identification test (UPSIT). MDS-UPDRS motor assessment was performed in the dopaminergic “off” state. Subscores for the cardinal motor symptoms (tremor, rigidity, axial and distal bradykinesia) were calculated.

Results: The mean UPSIT score was 16.3±8.2 (range 0-36) and the mean MDS-UPDRS motor score was 32.6±14.1 (8-72). Bivariate correlation analysis between the UPSIT and total MDS-UPDRS motor scores was significant (R=-0.23, P=0.0054). Stepwise regression analysis using the UPSIT as outcome parameters and the four rank-normalized MDS-UPDRS motor sub-scores showed a significant model with rigidity (F=10.32, P=0.0016) as the only significant motor parameter in the model (F=9.7, P=0.0022). Multiple regression analysis using the rank-normalized rigidity scores as outcome parameter and UPSIT, age and duration of motor disease as regressors yielded a significant total model (F=4.83, P=0.0031) with significant regressor effects for UPSIT scores (F=8.87, P=0.004), duration (F=3.91, P<0.05) but not for age (F=1.19, ns).

Conclusions: Rigidity but not the other cardinal motor impairments associates with impaired odor identification in PD. The selective association between motor rigidity and hyposmia in PD may reflect a partially shared neural network underlying these symptoms. Findings may agree with recent observations of a mesolimbic-striatal loop that is part of a larger neural network underlying rigidity in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/motor-rigidity-selectively-associates-with-impaired-odor-identification-in-parkinsons-disease/