EMG for Back Pain and Leg Pain

In the exam room, a neurologist can be about 90% certain whether a particular nerve is injured, and where. But to be sure, EMG for back pain and leg pain, or for neck pain and arm pain, needs to be done. The neurologist will check reflexes and muscle strength in different areas of the body for signs of nerve injury at the nerve roots, where nerves emerge from the spinal cord. These simple tests, along with the patient’s report of any symptoms they have observed, form a pretty complete picture of what is going on.

EMG for back pain and leg pain, or for neck pain and arm pain, helps to get the last 10% of certainty about the location of nerve injury, and excludes injured nerves in the arm or leg. To find out the exact cause of injury, as well as prognosis for recovery, the neurologist relies on imaging tests – MRI for soft tissues and x-ray for bone –. The x-ray allows us to see the spaces between bones that the nerve passes through, and is the only imaging test allowing weight bearing with flexion and extension of the spine, to see if there is visual movement of the spine that damages nerves and puts the discs under more stress. The MRI shows soft tissues like the nerve and disc, and whether there is swelling indicating injury. By comparing the MRI and x-ray images, we get a pretty clear picture of what structure is pressing on the nerve.

But the imaging doesn’t tell you how the nerve is doing.

Here at the RNI we have the ability to perform both imaging and EMG, in order to get the complete picture.

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EMG for back pain and leg pain, and for neck pain and arm and hand pain, tells us how badly the nerve itself is affected and makes sure no other nerves are damaged

While pain is a strong motivator for patients, many patients try to live with pain. They often wait to see a doctor until another symptom alerts them to the possibility of long-term implications of the back or neck problem causing that pain. They, and the neurologist, need to know if long-term or irreversible damage is being done to the nerve’s function.

Electromyography, or EMG, is the best test for assessment of nerve health and function throughout the body. It tests the ability of a specific nerve to transmit signals back and forth between the brain and parts of the body quickly and efficiently. You can think of it as an electrician checking the wiring inside of a wall to see why a light won’t come on.

Unlike the house wiring analogy, however, nerves aren’t simply “working” or “not working.” Unless it is completely severed, a nerve will always conduct some electrical signal, or current. The key to assessing the severity of an injury along a nerve is to measure how much current it can conduct (amplitude) and whether there is a delay. (Both are measured compared to the normal values for that particular nerve.)

Delay is measured in the “nerve conduction” part of the EMG test. In a healthy nerve, a single electrical impulse, like a little wave, runs along it when a signal is sent. In an injured or pinched nerve the wave moves slower, which can be measured in the time it takes an impulse to travel from one point to another. Such delays can be the cause of weakness, or of absent reflexes.

Amplitude of a nerve impulse is the other measurement we study. Each nerve fiber is capable of carrying a particular (and very small) electrical current. With a great many individual fibers bundled into a single nerve, the signal is larger. Measuring how large this amplitude signal is tells us how many individual nerve fibers are carrying current in that nerve. If the amplitude is smaller than it should be, compared to normal or the one on the other side of the body, we know that some fibers may not be conducting at all. EMG can even give us insight into which of these microscopic fibers are not conducting, which offers further confirmation of what we see in the x-ray and MRI images.

A strong, un-delayed impulse is critical for the skeletal muscles to do their work, so that you can move around and do the things you need to do.

What can I do If I can’t come to the Rowe Neurology Institute in Lenexa KS or Los Angeles?

Dr. Vernon Rowe has a web-based informational website that provides in-depth information about each of the neurological conditions that we specialize in, including informational videos like this one, with transcripts, that are unlike anything else on the web–they are NOT SPONSORED by any pharmaceutical company or other commercial entity. Go to DOCTORROWE.COM. The information provided will help you navigate your care wherever you go, with knowledge about the questions you should ask your doctor, and the tests that may be recommended, as well as some tips on how to obtain cost effective care, wherever you live.

by Vernon Rowe, M.D.
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