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, includingradiculopathy,[4] inflammatory myopathy,[5] Duchenne muscular dystrophy,[6] and spinal muscular atrophy.[7]
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[8] and individuals with orthopedic injuries[9] indicates that EIM is very sensitive to muscle atrophy and disuse and is conversely likely sensitive to muscle conditioning and hypertrophy.[10] Work on mouse and rats models, including a study of mice on board the final Space Shuttle mission (STS-135),[11] has helped to confirm this potential value.
ALS
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease and motor neurone disease (MND), is a specific disorder that involves the death of neurons that control voluntary muscles.[1][2][3][4] Some also use motor neuron disease for a group of five conditions of which ALS is the most common.[5] ALS is characterized by stiff muscles, muscle twitching, and gradually worsening weakness due to muscles decreasing in size.[6] This results in difficulty in speaking, swallowing, and eventually breathing.
Brawn and Brains
The scientists focused on the twins’ muscles rather than their exercise habits largely because the power measures were objective, unlike people’s notoriously unreliable recollections of how much they have worked out. (There was a correlation, though, between more self-reported exercise and sturdier legs.)
The scientists then asked the twins to visit a laboratory and repeat the cognitive tests.
Twenty of the identical twin pairs also completed brain-imaging scans.
Then the researchers compared leg power 10 years earlier with changes in brain function over the same time period.
They found that of the 324 twins, those who had had the sturdiest legs a decade ago showed the least fall-off in thinking skills, even when the scientists controlled for such factors as fatty diets, high blood pressure and shaky blood-sugar control.
The differences in thinking skills were particularly striking within twin pairs. If one twin had been more powerful than the other 10 years before, she tended to be a much better thinker now.
In fact, on average, a muscularly powerful twin now performed about 18 percent better on memory and other cognitive tests than her weaker sister.
Similarly, in the brain imaging of the identical twins, if one genetically identical twin had had sturdier legs than the other at the start of the study, she now displayed significantly more brain volume and fewer “empty spaces in the brain” than her weaker sister, Dr. Steves said.
Over all, among both the identical and fraternal twins, fitter legs were strongly linked, 10 years later, to fitter brains.
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