Assessing neuromuscular disease with multifrequency electrical impedance myography
Electrical impedance myography (EIM) is a noninvasive technique for neuromuscular assessment in which low-intensity alternating current is applied to a muscle and the consequent surface voltage patterns are evaluated. Previous work using a single frequency of 50 kHZ has demonstrated quantitative correlation of EIM parameters with disease status. In this investigation we examined the use of multifrequency EIM, studying a prototypical neurogenic disease (amyotrophic lateral sclerosis, ALS) and myopathic disorder (inflammatory myopathy, IM). Eleven ALS patients, 7 IM patients, and 46 normal subjects participated in the study. Although disease-specific patterns were not identified such that IM could be differentiated from ALS, impedance vs. frequency patterns for diseased subjects differed substantially from those of the age-matched normal subjects, with the greatest alterations occurring in the most severe cases. Multifrequency EIM may be well-suited to serve as an easily applied technique to assess disease severity in a variety of neuromuscular conditions.