Preserved diaphragm thickness and tidal contractility despite motor impairment in early-stage Parkinson's disease

Parkinson's Disease (PD) is a progressive neurological disorder associated with respiratory dysfunction, including inspiratory muscle weakness that contributes to morbidity and mortality. Despite this, the contributory role of the diaphragm remains unclear. This study assessed diaphragm thickness and contractility during tidal breathing in early-stage PD compared with matched controls using ultrasound imaging.

Twelve participants with early-stage PD (mean age 66.75 +/-8.07 years, mean disease duration 5.33 +/-5.6 years, Hoehn and Yahr stage 2), and twelve matched controls were assessed. Ultrasound measures included diaphragm thickness at end expiration (Tdi_exp), end inspiration (Tdi_insp), and contractile thickness (Tdi_insp-Tdi_exp). Contractility was evaluated using thickening ratio (DT_r), thickening fraction (DT_f), and contraction speed (mm/sec). Dyspnoea and respiratory disability were assessed using self-report and the Modified Medical Research Council (mMRC) scale. Correlations between diaphragm measures, motor severity using the MDS-UPDRS, and disease duration were explored.

Dyspnoea prevalence and mMRC scores were significantly higher in PD participants. Despite this, no significant between-group differences were observed for Tdi_exp (PD: 3.2 +/-0.77 mm; versus matched-controls: 3.01 +/-0.57 mm) or Tdi_insp (PD: 4.27 +/-0.95 mm versus 4.14 +/-1.06 mm) with small effect sizes. DTr and DTf were comparable between groups. Contractile thickness was lower (mean difference 0.03 mm), and contraction speed slower (mean difference 0.03 mm/sec), in PD with small effect sizes noted. No notable relationships between measures and PD disease duration were observed.

Diaphragm thickness and contractility appear maintained in early-stage PD despite increased dyspnoea. Further investigation in larger longitudinal studies across all PD stages and subtypes is required.