Temporalis Muscle Thickness as an Indicator of Sarcopenia Is Associated with Long-term Motor Outcomes in Parkinson's Disease

Background: To investigate the relationship between temporalis muscle thickness (TMT) at baseline as a surrogate marker for sarcopenia and long-term motor outcomes in patients with Parkinson's disease (PD). Methods: We enrolled 249 patients with drug-naïve early-stage PD (119 males and 130 females, follow-up > 3 years). Baseline TMT of each patient was measured on the axial plane of T1-weighted images. The association between baseline TMT and long-term motor outcomes in PD was assessed using Cox regression models for levodopa-induced dyskinesia, wearing-off, and freezing of gait and a linear mixed model for the longitudinal increases in levodopa-equivalent dose per body weight over time. Statistical analyses were performed separately for sex if an interaction effect between TMT and sex was assumed. Results: TMT differed substantially between the sexes, and male PD patients had higher TMT (6.69 ± 1.39 mm) than female PD patients (5.64 ± 1.34 mm, p <. 001). Cox regression models demonstrated that baseline TMT was not associated with the risk of developing levodopa-induced dyskinesia, wearing-off, or freezing of gait during the follow-up period. The linear mixed model was applied separately for sex and demonstrated that higher TMT at baseline was associated with slower increases in levodopa-equivalent dose per body weight in male PD patients, but not in female PD patients. Conclusions: This study demonstrated that baseline TMT could be an indicator of the longitudinal requirement for dopaminergic medications in male patients with PD, suggesting that sarcopenia may have a detrimental effect on disease progression in PD in a sex-specific manner.