Because it can test nerve function and determine the presence of nerve damage, electromyogram (EMG) testing may be more effective than magnetic resonance imaging (MRI) in diagnosing spinal stenosis as well as detecting the neuromuscular diseases that mimic stenosis, according to a new study in Spine.¹

The prospective masked, double-controlled diagnostic trial found that EMG can accurately differentiate spinal stenosis from low back pain even in patients who are asymptomatic, as well as diagnose neuromuscular diseases that may masquerade as stenosis. This will help reduce the incidence of misdiagnosed low back pain and other common neuromuscular conditions that have similar symptoms and help avoid unnecessary back surgery, according to lead author Andrew J. Haig, MD, associate professor in the department of physical medicine and rehabilitation at the University of Michigan Medical School in Ann Arbor, Michigan.

The new study of 150 participants aged 55 to 80 included patients with either low back pain (but no MRI evidence of spinal stenosis), spinal stenosis of varying severity, or no symptoms of either condition. Each patient first underwent a physical history, a physical examination, and an MRI. Physiatrists, neurosurgeons, and neuroradiologists then made a unanimous diagnosis about each patient's condition. The study then performed an EMG to determine the diagnostic specificity of the test versus the global assessment of the examination team.

EMG differentiates spinal stenosis from low back pain

EMG identified nerve or muscle disease in five participants whom medical experts all believed to have spinal stenosis. Overall, the results from EMG showed a substantial difference between the spinal stenosis patients and the two control groups.

EMG also successfully detected the common neuromuscular disease that can mimic spinal stenosis. The team's next study directly compares EMG and MRI to determine which test is best for detecting spinal stenosis. The research will also determine if either test can predict what happens to patients with back pain over time.

"Now we are finding out more and more that MRI cannot tell us why you hurt," Dr. Haig tells CIAOMed. "EMG detects disease that doctors didn't expect. Even when the doctor thinks everything is just great, EMG finds nerve disease that can mimic spinal stenosis," he says, explaining that "there have been so many skeptics because the science of studies of the use of EMG in back pain has been poor."

Although EMG technology has been around for about 60 years, there have been no controlled studies of EMG for spinal stenosis. Furthermore, many past studies of spinal stenosis had only looked at asymptomatic patients, while others failed to include comparison groups for patients with back pain or symptoms of spinal stenosis.

"Don't you dare look at the MRI until you have heard from the patients about their complaints," Dr. Haig advises, adding that leg pain and claudication should increase the index of suspicion. "If the patient says, ‘When I walk the pain in my back and leg get worse,' it points toward spinal stenosis, and if you need to find out, do an EMG," he says.

"If you think [the patient has] cancer of the spine or fracture, then do an MRI, Dr. Haig says, "but if there is cancer in the pelvis or other problems in the leg, a lumbar MRI won't pick them up, and that's where EMG becomes more useful."

EMG is markedly cheaper than MRI, Dr. Haig points out, and can be used in patients who are not candidates for MRIs due to obesity, claustrophobia, or other contraindications.

EMG is not without drawbacks, however. For example, Haig and colleagues point out, "it is more cognitively difficult to understand the details of an electrodiagnostic report in comparison to the visual MRI film."

Reference

1. Haig AJ, Tong HC, Yamakawa KSJ, et al. The sensitivity and specificity of electrodiagnostic testing for the clinical syndrome of lumbar spinal stenosis. Spine. In press.