What is a Nerve Conduction Study or EMG?
At Warner Orthopedics and Wellness, I often order nerve conduction studies in order to determine the source of either pain, sensory deficit, weakness, or neuropathy. Nerve conduction studies involved specialized equipment and are typically performed by certain physicians certified in their performance. I am not certified in the performance of EMG/nerve conduction studies, but I am very comfortable looking at the results and discussing the case with the consulting physician. Reviewing an EMG is much like reviewing an MRI; although the ordering physician does not have the equipment and technically does not perform the study, he or she is usually able to interpret the results. Typically, we select consulting physicians who are thorough and have a good knowledge and understanding of the neural anatomy involved and possible disorders that could be present that could be the source of pain. EMG/NCS studies must be done a certain way, in a room that is an appropriate temperature and the doctor will make sure that you are not on certain medicines and such. Many variables can affect the results and a good doctor will understand that as he or she performs the test for us.
It is important to do a thorough workup when dealing with people with musculoskeletal pain. Obviously, this is what we do at Warner Orthopedics every day all day. We treat pain from neck pain to head pain to shoulder pain to finger pain to toe pain, hip pain, ankle pain, and foot pain. Pain is essentially a signal brought by the nervous system to the brain and sometimes you need to test the nervous system itself or the circuits involved to see if they could potentially be contributing to the source of pain; that is what a nerve conduction study does for us. If pain is a signal in the brain, it is important to understand the structures that create that signal. The nerve conduction studies help us to do that.
The nerve conduction study typically involves two parts. There is a sensory part where surface electrodes that are small sticky pads (like what is used in a heart test) are placed on the limbs and these deliver and detect the electrical impulses coming from your nervous system. This is a generally safe study. It is well tolerated. There is minimal discomfort and people do well with this. The other side of the study is electromyelogram. Small needles are actually placed into various muscles that are associated with certain nerves that leave the spinal cords and nerve conduction from the muscle itself into the muscle can be tested. This is less comfortable than the sensory component of the test. There are certain techniques that have to be employed by the person performing the test to make it accurate. There should be no lotion or topical medication on the skin. The temperature should be warm as cold temperature slows the conduction velocity of the nerves and gives false positive results. Certain medications cause changes in nerve conduction studies, certain illnesses, and certain environmental factors. A good nerve conduction study doctor will understand all this and make sure that every factor that can be controlled is so that the results are accurate.
Nerve conduction studies can find disorders such as carpal tunnel syndrome or cubital tunnel syndrome “funny bone compression.” It can diagnose diabetic neuropathy or neuropathy from other sources. It can diagnose infection-related or trauma-related neuropathies. In addition, genetic disorders that involve the muscle and nerves can be detected and diagnosed with a nerve conduction study. One limit to nerve conduction studies, unfortunately, is that very small nerves are unable to be detected by this test. In these cases, if I am concerned about a neuropathy, I typically perform a skin biopsy and we actually send these to a laboratory where the number of nerve fibers in their quantity and quality are determined under a microscope. Indeed, skin biopsy is really the only way to diagnose small fiber neuropathy; this is a diagnosis that is very often missed. However, nerve conduction studies can detect and diagnose a fair number of disorders and are very useful when I am working up your musculoskeletal pain and functional limits. A nerve conduction study along with an electromyogram can determine if the pain in your foot is coming from the foot itself or if it is coming from a pinched nerve and the spinal cord. It is rare for heel pain to be from a pinched nerve in the spine, but it does occur and S1 compression at the level of the spinal cord can actually cause heel pain. Conversely, most pain that typically occurs in the foot does not come from the spine and that should be evaluated. The utility of the nerve conduction study and electromyogram is undisputed. I do not hesitate to consult physicians that perform this test for in cases where the source of pain must be determined with a greater degree of accuracy than simple imaging and physical exam. This information is often used for surgical planning and treatment purposes. This is a safe test which is done 100s and 1000s of times every day across the country. The needles are tiny. Most people do not notice them and the sensory part is obviously not uncomfortable to any significant degree. If I or another physician orders a nerve conduction study for you, hopefully this information will explain the test to you a bit more.