Reference values for 50-kHZ electrical impedance myography

Electrical impedance myography (EIM) is a method for non-invasively and quantitatively assessing muscle health, in which the major outcome parameter, phase (theta), decreases in diseased states. In order to create a set of normal reference values, we performed 50-kHZ EIM in 5 muscles of 87 healthy individuals, using theta as the major outcome variable. Because the distributions of data were mostly skewed, logarithmic transformations were performed, and the resulting data were fitted to quadratic functions. The lower limit of normal was set by plotting the lower 95% confidence interval of the curve for each muscle and then identifying age-specific reference values. We found that the distribution of data was similar to that for other neurophysiologic parameters. The lower limit of normal was easily defined, and relatively few values fell below the proposed lower limit. By using commercially available bioimpedance devices, these values will allow other investigators to explore the application of 50-kHZ EIM in clinical neuromuscular disease research.