Electromyography (EMG) and Nerve Conduction Study

Muscle and nerve testing helps diagnose damage and disease

Electromyography or EMG is a test of the responsiveness of your muscles to nerve signals. A nerve conduction study or NCS is a test to determine how quickly nerve impulses move throughout your nervous system. The tests are often performed together and may be recommended if you have any of the following in your arms, legs, back or another part of the body:

  • Cramping
  • Numbness
  • Pain
  • Tingling
  • Weakness

The doctor may refer to EMG and NCS to diagnose conditions such as:

A person who has suffered a sports injury, for example, may need an EMG and NCS to determine where the symptoms are coming from and how to best treat the injury. A person who has experienced some kind of trauma to the body, like a car accident, may need this type of testing to further diagnose injury.

The doctor may also rely on NCS to diagnose diseases, such as muscular dystrophy and Guillain-Barré syndrome, or to see how well you’re recovering from a nerve injury.

How EMG and NCS is done

If both procedures are being done at once, you will likely have the nerve conduction study first. This involves placement of an electrode (electrical patch) over the nerve area being tested. The technician delivers a mild electrical impulse to the nerve. If the impulse travels slowly, this may indicate nerve damage or disease. If the impulse travels freely, the nerve is likely to be healthy. Although a nerve conduction study can be helpful in diagnosis of nerve damage and disease, it is not always reliable as a patient may have nerve damage that is not reflected in the outcome of the study.

Electromyography also involves electrode patches on the skin in addition to insertion of a thin needle into the skin at key points of concern on the body. The person administering the test will ask you to flex (contract) and relax your muscles while an electrical signal is delivered. The technician is interested in seeing whether or not your muscles respond well to the nerve signals. Most people experience quick, sharp pain and discomfort during the EMG procedure as the needle goes in and the electrical impulse goes through the nerve. Fortunately, the test is over very quickly.

Preparing for EMG and NCS

Because of the electrode patches needing to be secured to the body, you’ll be advised not to use any creams or lotions before your EMG and NCS. You should also avoid any caffeinated beverages as well as any medications that affect your muscles, such as muscle relaxers. Your doctor may also advise you to stop taking certain medications in advance of your appointment.

Once the electromyography and nerve conduction studies are complete, the report will be sent to your doctor within a few days. Your doctor will then go over the results of your tests and help determine what the next steps should be.