If you’re experiencing muscle weakness or numbness, your doctor may recommend a nerve conduction study (NCS) and electromyogram (EMG) to help determine the cause.
These tests measure how well your nerves and muscles respond to signals from your brain. They can identify problems related to muscle tissue, nerves or places where nerves and muscles meet.
NCS and EMG can help diagnose many conditions, including:
Usually, a neurologist conducts both tests at the same time, starting with an NCS, followed by an EMG.
A nerve conduction study involves applying small electrodes on your skin near a nerve and then recording how strong the electrical activity is. If the signal is slow, your nerve may be damaged. You may experience a mild tingling feeling during this test.
For the EMG, a very thin needle electrode is inserted in your muscle. This may cause some minor discomfort. The electrode is connected to a machine that records signals traveling from your brain to your muscles.
A first reading is recorded while your muscles are relaxed. Additional readings are then taken while you slowly tighten and release your muscles. The electrode may be repositioned to record activity in different muscles. The entire procedure can take up to an hour and a half.
Following the procedure, you may be tender and swollen in and around the examination sites. Applying an ice pack to the tender areas or taking over-the-counter pain medicine may be helpful. You should be able to continue with normal activities after the tests.
Before having an EMG, tell your doctor if you have a pacemaker or if you’re taking any medicines. Some medications can impact the results of the test.
Take a bath or shower the morning of the test to remove oil from your skin, and don’t apply any creams or lotions.