How Can Electromyography Help Diagnose LEMS?

One test that can help diagnose Lambert-Eaton myasthenic syndrome (LEMS) — a rare disease characterized by progressive muscle weakness — is an electromyography test. This test, known as an EMG, measures the electrical energy produced by the nerve cells that control muscle contraction.

Here are some frequently asked questions, and their answers, about an EMG and how it can help diagnose LEMS.

What do I need to do before the EMG?

There is little preparation needed for an EMG. You don’t need to fast prior to the test, but you may need to avoid caffeine or nicotine for a few hours before having it done.

Wear comfortable clothing and do not use lotion on the targeted area prior to the test. You also will be asked to remove any metal you are wearing. This includes glasses, jewelry, watches, and hairpins.

Let your doctor know every medication and supplement you are taking prior to having the test. It also is very important that you let your doctor know if you have a pacemaker.

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What is going to happen during the EMG?

During the test, a fine needle will be inserted into a large muscle — usually a leg muscle. A “ground” electrode may be placed under the leg. The instrument used for an EMG will measure the electrical signal produced by the nerve cells while the muscles are at rest. The physician will then tell you to gently tense the muscle, and then to strongly tense the muscle. This may be repeated several times, and several muscle groups may be tested during the EMG.

Does the EMG hurt?

The needle insertion can hurt — much like getting an injection. If it is very painful, let the physician know immediately, as this can interfere with the test. The points at which needles were inserted may ache for a day or so afterward, much like an injection, but this should pass after a few days. If you experience severe pain, let your doctor know immediately.

How are the results going to be interpreted?

In LEMS, the signal produced by the nerve cell is weaker than normal. However, after a strong muscle contraction, the nervous signal goes up to normal. This can differentiate LEMS from other muscular disorders in which the nerve signal is weak from the beginning, and stays weak throughout the test.

Are there any complications associated with the EMG?

Complications are rare, but can include bleeding, infection, and nerve injury. If you experience discomfort during or after the procedure, inform your doctor. Following the procedure, if you develop a fever, or have swelling or severe discomfort around the site of injection, you should contact your doctor. These may be a sign of infection.

Last updated: Sept. 24, 2019

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