Diagnostic Health Corporation

EMG and NCS

What Are EMG and NCS?

Electromyography (EMG) and nerve conduction studies (NCS) are special tests used to detect neuromuscular disorders. An EMG measures the electrical activity of muscles, and NCS measure the speed and intensity of electrical signals that travel through nerves and the time it takes muscles to respond to these signals. Nerve conduction studies also are referred to as nerve conduction velocity tests (NCV).

Why EMG and NCS Are Important

These tests function as important diagnostic tools and provide vital information about the health of your nerves and muscles. They can detect the cause of such problems as muscle weakness, numbness, spasms, paralysis or pain. They also determine if the problem involves the nerves, muscles, spinal cord or brain.

How EMG and NCS Function

Both nerve and muscle cells produce minute amounts of electricity. Nerves send electrical impulses to muscles, instructing them to contract or relax. If nerves or muscles are affected by injury, disease or another condition, their electrical activity changes.

How EMG and NCS Equipment Detects Changes

Electrodes record the electrical activity of muscles or nerves, and then the data is displayed, analyzed, stored and printed by a computer. The monitor displays the electrical activity in wave patterns, and speakers audibly broadcast the activity.

What EMG and NCS Diagnose

These tests are used to detect the following:

  • Pinched nerves and inflamed muscles due to injury, a ruptured disk, disease or other conditions
  • Carpal tunnel syndrome, characterized by pressure on a major nerve that causes pain in the wrist or hand
  • Primary muscle disorders such as muscular dystrophy (a disease that causes certain muscles to atrophy, or waste away)
  • Neuromuscular disorders such as myasthenia gravis (a dysfunction in nerve impulses that leads to chronic muscle weakness)
  • Nerve disorders such as amyotrophic lateral sclerosis (commonly known as Lou Gehrig's disease)

How to Prepare for EMG and NCS

On the day of your test, bathe or shower as per your normal daily routine. Wash your arms and legs well to remove body oils, and not use any bath oils, lotions or creams as they can interfere with your test.

Eat your regular meals at your usual times. However, you may be asked to avoid caffeine and tobacco products for a few hours before your test.

Inform your healthcare provider about all medications you are currently taking, especially any blood thinners. Also, tell your provider if you:

  • Bruise easily
  • Have hemophilia, diabetes or a skin infection
  • Have a pacemaker

Relax yourself to ensure accurate test results. Tensed muscles may disrupt a precise reading. To promote relaxation, you should:

  • Wear comfortable, loose-fitting clothing
  • Keep your arms and legs warm and relaxed
  • Talk about any feelings of anxiety or fear you may have

Upon your arrival at the healthcare facility, your medical history will be charted. Please describe any present symptoms and past illnesses. You also may have a brief physical examination to study your nervous system, muscles and reflexes.

The EMG Procedure

Some procedures may vary, but most follow these guidelines:

While seated or lying down, certain areas of your skin may be cleaned.

One or more needle electrodes are gently inserted into the muscle. You may experience some discomfort such as a dull ache or pressure as the electrode is inserted. The other electrodes are attached to your skin.

The muscle is tested while at rest. Typically, there is no electrical activity within a resting muscle, and your healthcare provider may reposition electrodes to obtain readings from different sections of muscle.

The muscle is tested when you are asked to flex. This records electrical activity, which is normal within a contracted muscle. Again, the electrodes may be moved.

The choice of which other, if any, muscles will be tested will depend on your symptoms.

The duration of the test ranges from about 30 minutes to more than an hour.

After Your EMG

Recovery and return to your activities of daily living may involve the following:

You may feel soreness or tenderness in the tested muscles for a few hours afterward.

If you do feel discomfort, apply ice or a cold pack, but do not apply ice directly to the skin. Instead, wrap the ice in a cloth.

Be sure to ask your healthcare provider about taking a pain reliever.

You may return home or to your hospital room. Contact your healthcare provider for the test results. They usually are available within 24 hours.

The NCS Procedure

As with the EMG test, some procedures may vary. Most follow these guidelines:

Most patients are asked to lie down, although some may be asked to sit. This will depend on the area of your body to be tested. Certain areas of your skin may be cleaned.

A gel may be applied to your skin before recording electrodes are attached. Other electrodes will be attached for electrical grounding and to serve as reference points.

Stimulating electrodes will be held against your skin.

Responses to tiny electrical signals sent through your nerves are recorded. You may experience a tingling sensation - as when you hit your "funny bone" - or your muscles, fingers, or toes may twitch. While this tiny "shock" is unusual, it is also harmless.

The stimulating electrodes are moved to other areas, and additional testing is performed.

The total time needed for the procedure is about 15-to-30 minutes.

After the NCS test, your skin may be cleaned, and you may return home or to your hospital room. Contact your healthcare provider for your results. They usually are available within 24 hours.