Convenient Quantification of Myopathic Change in Muscle Via Electrical Impedance Myography

Magnetic resonance imaging (MRI) is an important clinical tool for tracking skeletal muscle disease and response to therapy in a variety of conditions ranging from muscular dystrophy to myositis. MRI can serve as a surrogate measure of skeletal muscle pathology; it can quantify atrophy, edema, fatty infiltration, and myofiber disorganization, obviating the need for biopsy. There is little question that tracking MRI changes will speed therapeutic clinical trials in many muscle diseases; its use has been strongly encouraged. Although MRI can provide excellent assessment of muscle condition, MRI has many drawbacks including high cost, general inconvenience, need for the subject to lie flat without moving, limited evaluation of upper extremity muscles, need for detailed image analysis to distill complex imaging data down to a simple value for disease tracking, difficulty obtaining repeated measurements in a clinical trial, and challenges in standardization of protocols across institutions. These limitations prevent MRI from being an easily applied biomarker for assessment of muscle health and disease status. A technology that offers compositional information similar to MRI but that overcomes MRI's many drawbacks could serve as an extraordinary powerful biomarker in regular patient care and clinical therapeutic trials.

Electrical impedance myography (EIM) is such a technology. In fact, EIM is currently being used as biomarker in a number of neuromuscular disorders. In EIM, using a small handheld device, a weak, directionally focused, multi-frequency electrical current is applied to a muscle, resulting surface voltages are measured, and impedance values are derived. Alterations in these values provide insight into the condition of muscle, including atrophy, edema, fatty infiltration, and myofiber disorganization. In addition to ALS, EIM has already shown considerable value as a biomarker in a number of disorders including muscular dystrophy, myositis, and simple deconditioning. In sum, the investigators hypothesize that EIM has the potential to serve as a proxy for MRI, providing much of the same information but with far greater speed and convenience, lower cost, smaller size, greater flexibility and tolerability and without the need for cumbersome image analysis.

While much data has been acquired showing EIM is sensitive to muscle health, there is only sparse data relating EIM directly to MRI. Given the complexity of both EIM and MRI, applying machine learning approaches to these data sets can serve as a means for establishing a relationship between these two technologies. This would allow EIM to serve as an extremely convenient tool for tracking muscle health and potentially as a biomarker in future clinical therapeutic trials and day-to-day patient care.

Research Question: Can EIM supplement and potentially substitute for MRI in the assessment of primary diseases of skeletal muscle (myopathies)?