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Electrical Impedance Myography, or EIM, is a non-invasive technique for the assessment of muscle health that is based on the measurement of the electrical impedance characteristics of individual muscles or groups of muscles. The technique has been used for the purpose of evaluating neuromuscular diseases both for their diagnosis and for their ongoing assessment of progression or with therapeutic intervention. Muscle composition and microscopic structure change with disease, and EIM measures alterations in impedance that occur as a result of disease pathology.〔 EIM has been specifically recognized for its potential as an ALS biomarker (also known as a biological correlate or surrogate endpoint) by (Prize4Life ), a 501(c)(3) nonprofit organization dedicated to accelerating the discovery of treatments and cures for ALS. The ($1M ALS Biomarker Challenge ) focused on identifying a biomarker precise and reliable enough to cut Phase II drug trials in half. The prize was awarded to (Dr. Seward Rutkove ), chief, Division of Neuromuscular Disease, in the Department of Neurology at Beth Israel Deaconess Medical Center and Professor of Neurology at Harvard Medical School, for his work in developing the technique of EIM and its specific application to ALS. It is hoped that EIM as a biomarker will result in the more rapid and efficient identification of new treatments for ALS. EIM has shown sensitivity to disease status in a variety of neuromuscular conditions, including radiculopathy, inflammatory myopathy, Duchenne muscular dystrophy,〔1: Rutkove SB, Geisbush TR, Mijailovic A, Shklyar I, Pasternak A, Visyak N, Wu JS, Zaidman C, Darras BT. Cross-sectional evaluation of electrical impedance myography and quantitative ultrasound for the assessment of Duchenne muscular dystrophy in a clinical trial setting. Pediatr Neurol. 2014 Jul;51(1):88-92. doi: 10.1016/j.pediatrneurol.2014.02.015. Epub 2014 Feb 28. PubMed PMID 24814059; PubMed Central PMCID: PMC4063877.〕 and spinal muscular atrophy.〔1: Rutkove SB, Gregas MC, Darras BT. Electrical impedance myography in spinal muscular atrophy: a longitudinal study. Muscle Nerve. 2012 May;45(5):642-7. doi: 10.1002/mus.23233. PubMed PMID 22499089.〕 In addition to the assessment of neuromuscular disease, EIM also has the prospect of serving as a convenient and sensitive measure of muscle condition. Work in aging populations〔http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3895401/〕 and individuals with orthopedic injuries〔Tarulli AW, Duggal N, Esper GJ, Garmirian LP, Fogerson PM, Lin CH, Rutkove SB. Electrical impedance myography in the assessment of disuse atrophy. Arch Phys Med Rehabil. 2009 Oct;90(10):1806-10. doi: 10.1016/j.apmr.2009.04.007. PubMed PMID 19801075; PubMed Central PMCID: PMC2829834.〕 indicates that EIM is very sensitive to muscle atrophy and disuse and is conversely likely sensitive to muscle conditioning and hypertrophy.〔http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3044213/〕 Work on mouse and rats models, including a study of mice on board the final Space Shuttle mission (STS-135),〔1: Sung M, Li J, Spieker AJ, Spatz J, Ellman R, Ferguson VL, Bateman TA, Rosen GD, Bouxsein M, Rutkove SB. Spaceflight and hind limb unloading induce similar changes in electrical impedance characteristics of mouse gastrocnemius muscle. J Musculoskelet Neuronal Interact. 2013 Dec;13(4):405-11. PubMed PMID 24292610.〕 has helped to confirm this potential value. == Underlying Concepts == Interest in electrical impedance dates back to the turn of the 20th century, when physiologist Louis Lapicque postulated an elementary circuit to model membranes of nerve cells. Scientists experimented with variations on this model until 1940, when Kenneth Cole developed a circuit model that accounted for the impedance properties of both cell membranes and intracellular fluid. Like all impedance-based methods, EIM hinges on a simplified model of muscle tissue as an RC circuit. This model attributes the resistive component of the circuit to the resistance of extracellular and intracellular fluids, and the reactive component to the capacitive effects of cell membranes. The integrity of individual cell membranes has a significant effect on the tissue’s impedance; hence, a muscle’s impedance can be used to measure the tissue’s degradation in disease progression. In neuromuscular disease, a variety of factors can influence the compositional and micro structural aspects of muscle, including most notably muscle fiber atrophy and disorganization, the deposition of fat and connective tissues, as occurs in muscular dystrophy, and the presence of inflammation, among many other pathologies. EIM captures these changes in the tissue as a whole by measuring its impedance characteristics across multiple frequencies and at multiple angles relative to the major muscle fiber direction. In EIM, impedance is separated into resistance and reactance, its real and imaginary components. From this, one can compute the muscle’s phase, which represents the time-shift that a sinusoid undergoes when passing through the muscle.〔 For a given resistance (R) and reactance (X), phase (θ) can be calculated. In current work, all three parameters appear to play important roles depending exactly on which diseases are being studied and how the technology is being applied.〔 EIM can also be impacted by the thickness of the skin and subcutaneous fat overlying a region of muscle.〔http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543755/〕 However, the electrode designs and can be created that can circumvent the effect to a large extent and thus still provide primary muscle data.〔http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3984469/〕 Moreover, the use of multifrequency measurements can also assist with this process of disentangling the effects of fat from those of muscle.〔http://www.clinph-journal.com/article/S1388-2457(14)00256-9/abstract〕 From this information, it is also becomes possible to infer/calculate the approximate amount of fat overlying a muscle in a given region. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electrical impedance myography」の詳細全文を読む スポンサード リンク
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