Electromyography, commonly referred to as an EMG, refers to an electrical study of muscle. It is a type of electrodiagnostic testing used to help determine if there is evidence of nerve or muscle injury contributing to your symptoms. It is critical to be able to evaluate the nerves when dealing with spinal problems or other musculoskeletal issues. Specialized nerve tests, called Electromyography (EMG) and Nerve Conduction Studies, are designed to diagnose abnormalities in the functioning of nerves.
How does the nervous system work?
The nervous system includes the brain, the spinal cord, and all the connections from the spinal cord to the muscles. It works like an electric circuit. The brain thinks and plans an action, such as lifting your foot to walk. Planning this move generates an electric signal that travels to the spinal cord. The spinal cord works like a switchboard, and its job is to direct this signal to the muscles needed to lift your foot. The signal travels out of the spinal cord through the nerve roots, which then bundle together to form plexuses before emerging in the arms and legs as smaller nerves. In this example, the nerves in the leg directly pass the electric signal to the muscles that lift your foot, and the process planned in your brain finally happens. While it seems like a long way for a signal to travel, the time between thinking about lifting your foot and seeing your foot leave the ground is almost none—unless there is a problem somewhere in the nervous system.
What is an EMG test used to diagnose, and why would I need one?
Let’s say that you cannot lift your foot off the ground regardless of how much you think it. Is this weakness due to a problem with the brain? Is it the spinal cord? Nerve root? Plexus? Nerve in your leg? Muscles in your leg? An EMG can help us answer those questions.
Here are some conditions an EMG can help diagnose:
How do I prepare for an EMG?
On the day of your test you may still wash your skin with soap and water, but do not rub any topical lotions on the arms or legs that are being tested. We will be placing sticky electrodes on your skin, and lotion may cause them to slip off rather than stick. Also, if you are prone to having cold hands or feet, try to wear warm gloves or socks on the day of your test.
How is an EMG performed?
An EMG is a two part procedure. The first part, the nerve conduction studies, tells us about the health of the nerves in the extremities. We mimic the electric signal from your spinal cord with a small electric shock at one part of the nerve and record that impulse at another part of the nerve or at a muscle supplied by that nerve. This part tells us if the individual nerve is conducting that electric signal properly. What you will feel when we stimulate is a small stinging sensation that goes down the arm or leg.
The second part, electromyography (EMG), involves placing a small needle with a microphone into several of your muscles. We listen to the muscles while they are resting and while they are active. This part tells us if the muscles are injured, and the pattern of injured muscles can determine if the problem is in the nerve in the extremity, the nerve root, the nerve plexus, or the muscles. You may feel discomfort with the needle in your muscles. This sensation tends to be similar to acupuncture or dry needling.
Taken together, these tests can tell us where in the nervous system the signal is interrupted on the way from the brain to the muscles in your foot.
How Long Does an EMG Take?
An EMG can last anywhere from half an hour to an hour and a half, depending on what question we are trying to answer. Based on what we are finding, sometimes we may have to add a couple extra nerves or muscles, which may make the test last longer.
What are the limitations/risks?
What an EMG cannot tell us is whether the problem is in the brain or the spinal cord itself. We rely on imaging of the brain and the spinal cord to show us problems there. The risks of an EMG are minimal. While in theory a punctured lung is possible, it is very rare that we have to stick a needle in a muscle anywhere near the lungs when we are checking your arms and legs. The needles are so small that permanent neurologic injury by nicking a nerve is very unlikely. Some patients will have minor bleeding, but it usually stops within a few seconds. What we see most often is that the muscles we sampled with the needle tend to be sore for hours or a day before returning to normal. But the information we gain from doing the test can help determine the best treatment path for you.