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 (ρ=0.79, p<0.001), surpassing that of MUNE (ρ=0.57, p=0.020). These two measures were also strongly correlated (ρ=-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.