Parkinson’s disease (PD) leads to accelerated declines in mobility, with rigidity being a major contributing factor. The development of objective measures of rigidity would be invaluable in the diagnostics and application of interventions. The purposes of this study were to determine the influence of PD on muscle stiffness, measured by shear wave elastography (SWE), in PD compared to healthy controls (CON); analyze SWE correlations in PD subjects; and explore SWE across Hoehn and Yahr (H&Y) stage and by medication status. Thirty PD (70.1±8.6 y; H&Y stages 1-4) and 24 CON (71.6±8.6 y) subjects participated in this study. A subgroup of eleven PD participants were tested both on and off medication. Clinical assessments included H&Y stage, disease severity, and rigidity, whereas performance measures included mobility, strength, and power. Ultrasound SWE measurements were taken for the tibialis anterior (TA), medial gastrocnemius (MG), and lateral gastrocnemius. TA SWE was significantly greater in PD than CON (p = .03) and correlated to ankle rigidity (r = .543), whereas MG SWE was significantly associated with H&Y stage (r = -.398), disease severity (r = -.483) and lower limb rigidity (r = -.371). No other significant results were found, although trends showed higher SWE off than on medication. The TA was more sensitive than the gastrocnemii in the assessment of muscle stiffness in persons with PD, and reduced MG stiffness was associated with increased disease stage and severity. Results suggest that SWE is a viable method for the evaluation of rigidity and disease progression in PD.

Authors: Keri L. Strand, Kevin A. Jacobs, Moataz Eltoukhy, Corneliu C. Luca, Joseph F. Signorile