Ultrasonographic assessment of oral-phase swallowing function in Parkinson’s disease

Dysphagia (swallowing difficulty) is commonly observed in patients with Parkinson’s disease (PwPDs), often leading to complication such as aspiration pneumonia. Although ultrasonography is a non-invasive and easily applicable method that allows real-time evaluation of functional structure, evidence for utility of the assessment to evaluate swallowing function in PwPDs remains limited. This study aimed to evaluate the diagnostic potential of ultrasonography for detecting dysphagia in PwPDs and to examine its relationship with tongue pressure, geniohyoid muscle morphology, and swallowing function compared with younger healthy controls. A single-center, prospective, cross-sectional clinical study was conducted. 22 PwPDs (mean age 69.2 ± 9.1 years) were recruited and divided into two groups based on the presence or absence of dysphagia. Additionally, 24 younger healthy participants (mean age 30.8 ± 8.5 years) were enrolled as a reference group. Swallowing function was assessed using ultrasonography across six parameters: resting geniohyoid muscle (GM) thickness, resting GM cross-sectional area, GM contraction time, number of contractions, and velocity at first contraction (upper and lower). Statistical analyses were performed as follows: between-group comparisons were conducted using the Mann–Whitney U test, associations between variables were assessed using Spearman’s rank correlation, and multiple linear regression analyses and receiver operating characteristic (ROC) curves were also performed. Twelve PwPDs without dysphagia (PDD-) and 10 PwPDs with dysphagia (PDD+) were identified. All PwPDs had smaller resting GM thickness and resting GM cross-sectional area than younger healthy participants. Additionally, the GM contraction time was prolonged and the number of contractions was increased in all PwPDs compared to younger healthy participants. Compared to PDD-, PDD+ exhibited significantly prolonged GM contraction time (PDD-: 1.66 ± 0.62 s vs. PDD+: 3.65 ± 2.94 s, p = 0.017), while no differences were observed in other parameters. Tongue pressure showed positive correlations with resting GM thickness and resting GM cross-sectional area, and negative correlations with GM contraction time and number of contractions. The number of contractions as a significant predictor of GM contraction time ( β = 0.950; p < 0.001). The area under the ROC curve for GM contraction time was 0.800 (95% confidence interval, 0.593–1.00). A cut-off value of 2.2 s based on the Youden index yielded optimal sensitivity and specificity of 0.700 and 0.833, respectively. This study demonstrated that the GM contraction time measured using ultrasonography can serve as a useful and novel screening parameter for evaluating oral-phase swallowing dysfunction in PwPDs. Further research is warranted to confirm its clinical utility and establish standardized protocols.