Electrical Impedance Myography for Evaluating Paretic Muscle Changes After Stroke

Electrical impedance myography (EIM) was used to assess the paretic muscle intrinsic electrical properties post stroke. Twenty-seven subjects with chronic hemiparesis participated in this study. Muscle impedance was measured by applying high-frequency, low-intensity alternating current to biceps brachii muscles. Major EIM parameters, resistance (R), reactance (X), phase angle (theta), and electrical anisotropy ratios (AR) of the three parameters, were examined at 50 kHz. Statistical analysis demonstrated significant reduction of reactance, phase angle, AR of resistance, and AR of reactance in the paretic muscle compared with the contralateral side (Paretic X: 6.16 +/- 0.55 Omega, contralateral X: 7.62 +/- 0.46 Omega, and p < 0.001; Paretic theta : 10.97 +/- 0.84 degrees, contralateral theta : 14.5 +/- 0.82 degrees, and p < 0.001; Paretic AR of R: 0.969 +/- 0.013, contralateral AR of R: 1.008 +/- 0.011, and p < 0.02; and Paretic AR of X: 0.981 +/- 0.066, contralateral AR of X: 1.114 +/- 0.041, and p < 0.02). Correlation analysis, however, did not show any significant relationship between EIM parameters and clinical assessments. Findings of this paper indicated significant changes in the muscular intrinsic electrical properties after stroke, possibly related to structural modifications induced by loss of muscle fibers or fat infiltration as well as changes in the quality of cell membranes post stroke.