Electrical impedance myography for monitoring motor neuron loss in the SOD1 G93A amyotrophic lateral sclerosis rat

Objective: Human studies have shown that electrical impedance myography (EIM), a technique based on the surface application of high-frequency, low-intensity electrical current to localized areas of muscle, is sensitive to muscle denervation. In this study, we examined the role of EIM as a potential biomarker for assessing ALS disease progression in the SOD1 transgenic rat by comparing it to motor unit number estimation (MUNE). Methods: Multi-frequency EIM and MUNE were performed twice weekly in 16 rats from approximately 10 weeks of age onward. Four different EIM measures were evaluated, including the previously studied 50 kHz phase and three condensed multi-frequency parameters. Results: The rate of deterioration in the multi-frequency phase data from 100-500 kHz had the strongest correlation to survival (rho = 0.79, p < 0.001), surpassing that of MUNE (rho = 0.57, p = 0.020). These two measures were also strongly correlated (rho = -0.94, p < 0.001) to one another. Conclusions: These findings support that EIM is an effective tool for assessing disease progression in the ALS rat. Significance: Given its ease of application and ability to assess virtually any superficial muscle, EIM deserves further study as a biomarker in human ALS clinical therapeutic trials. (C) 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.