Nerve conduction studies and EMG
Nerve conduction studies and EMG are medical diagnostic tests that measure the function of the nerves and muscles. They are used to diagnose common problems like carpal tunnel syndrome, ulnar neuropathy, pinched nerves in the spine as well as diseases of nerves and muscles, and conditions like ALS and myasthenia gravis.
You should only have these tests performed by a physiatrist or neurologist certified in performing these tests. In Canada certification is through the Canadian Society of Clinical Neurophysiologists (CSCN).
Most people and doctors say they are being sent for an “EMG”, but EMG is only one part of the test and in many cases is not required. Almost everyone coming for testing will undergo a nerve conduction study.
Nerve conduction study
Nerve conduction study is a way to conduct small amounts of electricity through the nerve and record responses through the skin. We use milliAMPs, which means there is actually very little electricity passing into the nerve. For this reason it is a very safe test. Almost all nerve and muscle problems require at least a basic screening nerve conduction study. We obtain information about how fast the nerve signals are travelling as well as how large the nerve signals are. When a nerve is being pinched (compressed) we can find slowed signals in a certain part of the nerve. We determine how severe the damage is by seeing how slow the signals are and if the damage has made the size of the responses smaller.
EMG is short for electro (electricity) myo (muscle) graphy (measurement). It is a way to record electricity directly from the muscle. Your muscles make chemical electricity and this test examines those electrical signals. The procedure requires a sterile wire inserted into the muscle. It is a small wire (like acupuncture); much smaller than a needle that is used to draw blood. It doesn’t inject or shock electricity, it just records the electricity from your muscle like a microphone.
Information gathered from EMG is used to determine if a nerve connected to that muscle has been damaged. When a nerve is damaged it changes the electrical signals in the muscle. It also gives some information about whether a nerve injury has been recent or more chronic, as well as some information about severity of nerve damage. In other conditions like muscle disease it alters the electrical signals in a different way that we can detect through this testing.
EMG testing is only done in some situations. For the most routine problems like carpal tunnel syndrome or ulnar neuropathy the most useful information is obtained from a nerve conduction study. EMG is usually unnecessary in those situations.
Are these tests painful? What does it feel like?
With nerve conduction study we use small amounts of electricity to stimulate the nerve. It feels sort of like when somebody shuffles across a carpet and touches somebody. The weird part is that because the nerve is connected to the muscle, the muscle will jump (contract) by itself very briefly. Occasionally there are places where nerves are deep and we use more intense levels of stimulation. Most people tolerate this part of testing very well.
Electricity sensations are experienced differently for each person. Like claustrophobia, or fear of spiders, or heights, there is something about how the brain is wired in different people. Occasionally there are people who find the sensation more uncomfortable because their brain is wired that way when they experience these electrical stimulations. Most people find it only mildly uncomfortable.
EMG wires are very small but it is still like getting pinched with a very small needle. Some mild achiness in the muscle during the testing is common and normal. For some people the muscle can feel sore and achy for a few hours afterwards. There are some parts of the muscle that are more sore than others. Sometimes we will have to change wire position to reduce discomfort.
Remember that you are the boss. We can slow down, take breaks, or quit at any time. You are in charge.