Differential associations between tongue pressure and handgrip strength with MDS-UPDRS part III motor symptoms in Parkinson's disease.

Tongue pressure is a swallowing-related measure that correlates with handgrip strength, an indicator used in the assessment of sarcopenia. However, reduced tongue pressure in Parkinson's disease (PD) may reflect not only generalized muscle weakness but also PD-related motor control impairment, raising the possibility that tongue pressure and handgrip strength may show different patterns of association with PD motor symptoms. This study examined the patterns of association between tongue pressure and handgrip strength and motor symptoms assessed using Part III of the Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) in patients with PD. A total of 49 individuals with PD aged 70-85 years were enrolled in this cross-sectional observational study. Tongue pressure, handgrip strength, and MDS-UPDRS Part III scores were assessed. Exploratory factor analysis of the MDS-UPDRS Part III items was conducted, followed by multiple regression analyses based on the total score and identified factors. After adjusting for age and sex, tongue pressure (β = -0.320, p = 0.021) and handgrip strength (β = -0.409, p = 0.025) were associated with the MDS-UPDRS Part III total score. Three motor symptom factors were identified: axial control and global motor output, limb motor function, and tremor. Tongue pressure was associated with limb motor function involving rigidity and bradykinesia, whereas handgrip strength was associated with axial control and global motor output. These findings suggest that reduced tongue pressure in patients with PD may reflect not only generalized muscle weakness but also specific aspects of PD-related motor dysfunction. However, given the cross-sectional nature of the study, further studies are required to better characterize the relationship between tongue pressure and PD motor symptoms.