Electromyography (EMG) at Cambridge Hospital

What are nerve conduction studies (NCS) and electromyography EMG?

These are tests of the peripheral nerves and muscles that are commonly used to help diagnose weakness, numbness and other symptoms. The term EMG (electromyography) is often used by clinicians to refer to both nerve conduction studies and EMG. There are many causes of weakness or numbness, so sometimes these tests need to be interpreted alongside scan results or other investigations. Not all the conditions that have abnormal nerve conduction or EMG are serious.

What happens before the investigation?

There are no special precautions required. There is no restriction on eating or drinking before, or after, the test. There is no restriction on driving after the test. Patients should continue to take their usual medication as prescribed.

Remember to tell your doctor about any of the following:

1. A pacemaker or implanted cardioverter or cardiac defibrillator
2. Any blood thinning medication such as warfarin, rivaroxaban or apixaban
3. An increased risk of bleeding or infection

Preparing for your test

• Wear loose-fitting clothing as the doctor will need to examine your arms or legs
• Avoid moisturising creams for the day of the test as they can interfere with the recordings
• It’s fine to have a partner or family member accompany you during testing

What happens during NCS?

1. Small sticky electrodes are attached to the skin to measure the ability of your nerves to conduct electrical signals
2. A short electrical pulse is applied to the nerve (lasting less than one-thousandth of a second) and the response is recorded. During this you will briefly feel a tapping sensation
3. The size, shape, and speed of responses from nerves that go to supply muscles, and others from the skin, is recorded.

What happens during EMG?

A single-use very fine, sterile, needle electrode is inserted into the muscle to record the electrical activity when it contracts.

Are there any risks?

Nerve conduction studies are very safe, and can still be performed in patients with pacemakers, and during pregnancy. Adjustments to testing may be made if the patient has a pacemaker or an implanted cardiac defibrillator.

After an EMG the muscle may feel slightly itchy or ache for a few minutes, and there may be a small bruise.

It is a very safe procedure, and significant complications due to bleeding are very rare (less than 1 in 10,000). You can return to your normal activities immediately after the investigation.

If the risks are higher than normal the doctor will discuss this with you to seek consent about how to proceed.