By Wesley A. Rowe and Vernon Rowe, M.D.
In the exam room, a neurologist can be about 80% certain whether a particular nerve is injured, and oftentimes where that nerve or nerve root is injured. But to be as sure as we can be, and since nerves and nerve roots are “electrical” circuits by their very nature, an electrical test is usually done to test those circuits. This test is called an EMG, which stands for Electromyogram.
An EMG is done by inserting tiny pin electrodes into certain muscles whose exact electrical connections are known. The EMG is always coupled with nerve conduction testing (NCV) to test the electrical conduction of specific nerves. Since both the EMG and NCV tests can be a little uncomfortable, it is important that they be carried out by a specially certified physician, so that only the necessary nerves are stimulated and tested to get to the bottom of the problem.
As in all cases, this testing must be carefully correlated with a patient’s clinical history and neurologic examination. The examining physician must check reflexes and muscle strength in different areas of the body, to determine exactly which muscles and nerves or nerve roots need to be tested. This same approach, of correlation of imaging studies like X-Ray and MRI, with a patient’s history and exam is also crucial for patient care, but this is covered elsewhere. After all, doctors should treat patients, not just their tests.
EMG for back pain and leg pain, or for neck pain and arm pain, helps to get the last 15-20% of certainty about the location of nerve injury, and when coupled with appropriate imaging testing, like X-Ray and MRI studies, allows the doctor to find out the exact cause of pain and injury to the nervous system.
For instance, appropriate X-Rays in the lying and standing with bending positions allows the doctor to see whether spinal instability caused by congenital defects and trauma is contributing to a patient’s problems. MRI, on the other hand, is taken in the supine or lying position, and shows soft tissues, like muscles, tendons, ligaments, and discs much better than X-Rays.
X-Ray and MRI examinations are always complementary to EMG-NCV examinations, since they give separate windows into any particular patient’s problems. By correlating the MRI and X-Ray images with the EMG-NCV testing and patient history and examination, doctors can get a pretty clear picture whether an abnormal structure is pressing on a nerve, and how much damage that structure is doing.
EMG-NCV testing for back and leg pain, and for neck and arm and hand pain, is the only objective test that can tell us how badly nerves are affected, can exclude damage to other nerves, and can tell whether irreversible damage has occurred
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.
Again, EMG-NCV testing is the best test for assessment of nerve health and function throughout the body. EMG-NCV tests the ability of a specific nerve to transmit signals to the muscles of the body, and whether the two parts of a nerve, the “wire” and the “insulation” are damaged. The tiny nerves which are un-insulated and transmit pain signals, can also be checked in this way. You can think of it as an electrician checking the wiring inside 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 completely severed, a nerve will always conduct some amount electrical signal, or current. The key to assessing the severity of an injury along a nerve is to measure how much current it does conduct (amplitude), and whether there is a delay. (Both are measured and compared to 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 often moves more slowly, and this can correlate with diminished reflexes on clinical exam, or specific muscle weakness.
Likewise, the amplitude of transmitted signals on EMG-NCV testing can help assess how many of the signals are getting through. 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 an insight into which of these microscopic fibers are not conducting, and this offers further confirmation of what we see in the x-ray and MRI images.
Go to DOCTORROWE.COM for additional information. This site will provide you with questions you may need to ask your doctor, suggested tests that may be recommended, and some some tips on how to obtain cost effective care, wherever you live.
by Vernon Rowe, M.D. –
Dr. Rowe on Google+
