Single and modeled multifrequency electrical impedance myography parameters and their relationship to force production in the ALS SOD1G93A mouse

ABSTRACT

Objective: The relationship between muscle force production in ALS SOD1G93A mice and single and modeled multifrequency electrical impedance myography (EIM) parameters is unknown. We evaluated the relationship between multifrequency EIM data and paw grip and in situ force measurements, as well to standard measures including body weight and compound motor action potential (CMAP) amplitude. Methods: Twenty-nine SOD1 G93A mice aged 13–18 weeks (approximately 4–5 per week) and a group of similarly aged wild-type mice (N = 7) were studied with single and multifrequency EIM, CMAP, front and hind-limb paw grip measures, and in situ force measurements of the gastrocnemius. Results: Significant differences among WT, presymptomatic, and symptomatic ALS animals were identified for all standard measures and single 50 kHz frequency EIM parameters. Of the modeled multifrequency measures, the center frequency, f_c , an index of cell size, showed the strongest relationship to force output. The two other multifrequency parameters corresponding to cell size distribution and cell density showed consistent although mostly non-significant differences. Conclusion: Reductions in force are reflected in single 50 kHz impedance values and in the f_c. These data support the construct validity of EIM as an assessment tool of muscle dysfunction in diseases associated with motor neuron loss.

Key words:

• Motor neuron disease
• amyotrophic lateral sclerosis
• compound motor action potential amplitude
• electrical impedance
• force

Acknowledgements

This work was funded by the National Institutes of Health R01 NS055099 and the Spinal Muscular Atrophy Foundation.

Declaration of interest: Jia Li-None; Benjamin Sanchez-None; Adam Pacheck-None

Seward Rutkove–Dr. Rutkove has equity in, and serves a consultant and scientific advisor to, Skulpt, Inc. a company that designs impedance devices for clinical and research use; he is also a member of the company’s Board of Directors. The company also has an option to license patented impedance technology of which Dr. Rutkove is named as an inventor.