Old Medical Technology Sheds New Light On Back Pain

November 01, 1997

ANN ARBOR---A 50-year-old medical test has proven more reliable than high-tech diagnostic tools in pinpointing some back disorders, according to a researcher at the University of Michigan Medical Center.

Electromyography, a test which has been around since World War II, measures the electrical signals sent out by muscles. By inserting thin needle electrodes into various muscles, an electromyographer can map out normal and abnormal signals and determine whether there has been subtle nerve damage or paralysis.

Electromyography (EMG) has been used less often with the advent of non-invasive tests such as CT scans and MRI scans. Those high-tech tests, however, often make diagnosis difficult by providing too much information, explains Andrew Haig, M.D., medical director of the Spine Program at the U-M Medical Center. MRI scans, for example, find "abnormalities" in two-thirds of people who are not experiencing back pain.

On the other hand, new research directed by Haig shows that EMGs are highly accurate without the "false positive" results common with CT and MRI scans. Haig describes his findings in the November issue of the Archives of Physical Medicine and Rehabilitation.

"The bottom line is that all the fancy modern tests provide too much information in diagnosing people with back pain," Haig says. "Fortunately, this very old test is finding new use in sorting out these problems."

In a second paper in the same edition of the journal, Haig discusses a method he has developed that eliminates three-fourths of the EMG needle insertions needed for an accurate diagnosis.

In earlier projects, Haig worked with cadavers to ascertain precisely how to insert needles into pencil-thin paraspinal muscles and also studied the different readings an EMG generates from people with back problems and those without back pain.

His new studies take that a step further by demonstrating that EMG tests can effectively diagnose problems in the paraspinal muscles and showing that a technique called "mini-paraspinal mapping" can accurately diagnose many back problems while reducing the number of EMG needle insertions from 45 to 12.

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University of Michigan

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