Measuring Muscles
A new handheld device could replace invasive techniques for evaluating muscle tissue and speed research on drugs for Lou Gehrig's disease.

By Eric Bland


Muscle meter: For seven years, researchers at Beth Israel Deaconess Hospital in Boston have been experimenting with a technique for evaluating muscle tissue by measuring its electrical properties with adhesive electrodes (shown here). A handheld device that uses the same technology promises to provide fast and accurate data about the condition of patients’ muscles.
Credit: Seward Rutkove


A team of Boston-area doctors, physicists, and electrical engineers is developing a handheld probe that measures the state of a patient's muscle tissue and should prove cheaper, faster, more accurate, and less painful than its predecessors. The probe will help neurologists diagnose and track the progress of neuromuscular diseases, and it could also speed up the development of drugs for diseases like Lou Gehrig's disease and muscular dystrophy. The probe, which measures electrical properties of muscle, should be available for clinical use early next year.

Currently, doctors evaluate patients' muscles using either strength tests, where patients push or pull against something, or a technique called electromyography. Strength tests, while efficient, are imprecise, and results vary depending on how well motivated patients are. In electromyography, a trained doctor or physical therapist inserts needle electrodes into the muscle in several different places and takes readings that last about three minutes each. The process is uncomfortable and takes anywhere from 20 to 30 minutes, during which the patients must remain still.

Since the new probe uses an electrical signal, it's both more accurate and more precise than strength tests. "This makes it a quantitative measure and is completely objective," says Northeastern University physics professor emeritus Carl Shiffman, whose work on electrical impedance with Ronald Aaron was one of the inspirations for the new device. "The patient doesn't even have to cooperate to get a good reading." And unlike electromyography, the new probe is noninvasive and uses very low voltages. It also requires little training to use and takes readings in seconds, not minutes.

Seward Rutkove, a neurologist at Beth Israel Deaconess Medical Center in Boston, MA, who led the probe's development, says that electromyography "is poor in judging how weak a muscle is. You can't really use it as a measure of how severe a problem is or if it is getting better." The new probe, he believes, will solve that problem. Initially, he says, it will probably be used to supplement electromyography, but in some cases--in children, for example--it could replace it entirely.

The probe is also relatively cheap: the whole system, Rutkove says, will cost an estimated $2,000 to $5,000, where an electromyography machine costs between $16,000 and $40,000.

The device uses a technique called electrical impedance myography, or EIM. It emits a weak alternating current that changes as it moves through muscle, since firm, healthy muscle conducts electrical charges more readily than less-used muscle, and fat acts as an insulator. The probe then measures the current at different locations parallel and perpendicular to the grain of the muscle. Together, these readings provide a detailed picture of the muscle's condition.

In the last seven years, Rutkove has used EIM to diagnose and evaluate more than 350 patients, relying on sticky electrodes that attach to the patients' skin and have to be moved for each measurement.

Now he is working with electrical engineers from MIT to make the system more portable, more efficient, and more accurate. The business end of the researchers' prototype, where the alternating current is released and detected, is a green circuit board with metallic circuits radiating out from the center. A white plastic housing encases brightly colored wires connected to batteries, and a wire leads back to an oscilloscope and wave-form generator. The researchers are working to replace the wire and oscilloscope with a standard USB connection to a laptop or, ultimately, a PDA.

Once the EIM probe is fully functional, it should take only a few seconds to gather data for each muscle, with the entire process taking a minute or two, says Roshni Cooper, an MIT graduate student in electrical engineering who has been working on the probe for the last seven months.

One disease that EIM is particularly useful for monitoring is amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease. ALS is a progressive neurodegenerative disease in which the brain cells that control muscle movement deteriorate and eventually die. With nothing telling the body's muscles when to contract, they stop--the heart and lung muscles included.

A patient who develops ALS typically lives three to five years. Drugs for treating ALS are under development, but the best quantitative test of their effectiveness is brutally straightforward: life span. If, on average, patients taking an ALS drug live longer than patients in a control group, then the drug is considered to work. This approach has drawbacks: the control patients may be denied life-extending treatments, and since ALS patients usually live for years after diagnosis, the results of the drug studies are slow to come in.

Researchers hope that EIM can cut down the time required to see a drug's effects. Faster drug approval would mean longer, more active lives for patients with ALS. With EIM, Shiffman says, doctors should be able "to see changes in patients' muscle within several months, instead of several years."


http://www.technologyreview.com/Biotech/19739/