Electromyography (EMG) is a medical testing technique used to measure electrical activity in a person’s muscles.
Muscles are controlled by nerves, which send and receive electrical signals from the brain and spinal cord that tell the muscles what to do. When nerves or muscles are malfunctioning or damaged, the levels of electricity in the muscles are different than the levels found in healthy muscles. By measuring these levels, doctors can determine if a person’s nerves, spinal cord and muscles are healthy and working properly, and might be able to diagnose related problems.
What is a Nerve Conduction Study (NCS)?
Like an EMG, a Nerve Conduction Study measures electrical activity. However, Nerve Conduction Studies test electrical activity in a person’s nerves, rather than their muscles.
A Nerve Conduction Study is used to see how fast electrical signals travel through nerves connected to the brain and spinal cord. The results may be used to uncover nerve damage or diagnose certain diseases.
When is it necessary to get an EMG test or Nerve Conduction Study?
EMGs and Nerve Conduction Studies both examine the condition of a person’s nerves. If doctors see signs of neuromuscular problems, they often order both tests.
When a person experiences weakness, paralysis or twitching in his or her muscles, these tests are often used to help identify the cause of the problem. They may also help to diagnose certain nerve-related diseases, such as Chronic Inflammatory Demyelinating Polyneuropathy (CIDP), Multifocal Motor Neuropathy (MMN) and Myasthenia Gravis (MG).
How is an EMG test?
The patient lies on a table, bed or reclining chair. A tiny electrode needle is inserted into the muscle being tested. The needle is connected by wires to a recording device. First, the needle measures the electrical activity of the muscle at rest. Then the technician asks the patient to slowly flex the muscle, and measures again. Tests may last for 30 to 60 minutes, and the electrode needle may be inserted in several places to test different muscles.
How is a Nerve Conduction Study done?
Patients undergoing a Nerve Conduction Study lie on a table, bed or reclining chair. A shock-emitting electrode is taped to the skin over the nerve being tested, and a recording electrode is taped to the muscle controlled by that nerve. Quick electrical pulses are sent through the nerve, and a device measures how fast it takes for the patient’s muscle to contract or flex. A Nerve Conduction Study usually lasts between 15 minutes and one hour, depending on the number of nerves that are tested.
How should one prepare for EMG testing and Nerve Conduction Studies?
Your doctor will provide a set of instructions to follow before each test regarding eating and drinking, smoking, the use of lotion, creams, or oils and what to wear. Before either test, it is important to tell your doctor if you are taking any medications. This?is particularly important during EMG testing, especially if you have a bleeding disorder, take blood thinners or use a cardiac pacemaker.
How does it feel?
Patients may experience minor discomfort during both tests, but most people find them to be easier than expected. Tests are performed by physicians or highly trained technicians, and occur at a hospital, clinic or doctor’s office in a controlled environment.
During EMG testing, patients may feel a quick pinch when the electrode needle is inserted, and may experience tingling or soreness in the muscle for one to two hours afterwards. In rare cases, patients with certain conditions experience minor pain during testing due to the electric current.
During a Nerve Conduction Study, patients may feel a small shock or tingling feeling and a twitch in the muscle being tested each time an electric pulse is given. Only low-voltage current is used and each electric pulse lasts for less than one second.
Anxiety is common, but staying relaxed often minimizes discomfort.