A  nerve conduction study (NCS) measures electrical impulses as they move through your nerves. A NCS can identify nerve damage. The nerve conduction study is done by a Neurophysiologist. This is a doctor who specializes in brain and nerve disorders.

Two sets of electrodes are placed on the skin over the nerve (or muscle) being studied - one set stimulates the nerve with a very mild electrical impulse and the other records the resulting electrical activity which is then recorded by a computer. This is repeated for each nerve being tested.

A related test that may be done is an electromyogram (EMG). This uses a fine-recording needle to measure the electrical activity in your muscles. It is usually done at the same time as a NCS. Both tests help find the presence, location and extent of diseases that damage the nerves and muscles.

Nerve conduction studies are performed to find the cause of symptoms such as weakness, numbness, tingling and pain. A NCS detects a problem with conduction in nerves, whereas an EMG detects whether the muscle is working properly. Diseases or conditions that may be checked with a NCS include:

• Carpal tunnel syndrome. A condition in which the median nerve, which runs from the forearm into the hand, becomes compressed at the wrist. It causes pain and numbness in the fingers.

• Chronic inflammatory polyneuropathy and neuropathy. These are conditions resulting from diabetes and other disorders. Symptoms may include numbness or tingling in the distribution of a single nerve or many nerves at the same time.

• Herniated disk disease. This condition occurs when the fibrous cartilage that surrounds the disks of your vertebrae breaks down. The center of each disk, which contains a gelatinous substance, is forced outward. This places pressure on a spinal nerve and may cause pain, numbness and weakness.

• Guillain-Barré syndrome. A condition in which the body's immune system attacks part of the peripheral nervous system. The first symptoms may include weakness or a tingling sensation in the legs.

• Charcot-Marie-Tooth disease. An inherited neurological condition that affects both the motor and sensory nerves. It causes weakness of the distal muscles.

• Eat and drink normally before the study. Fasting is not required.

• Dress in clothes that allow access to the area to be tested - clothes that can be easily rolled up to expose most of the arm or leg being tested. You will be provided with a gown if clothing needs to be removed.

• Avoid the use of skin moisturisers prior to the test.

• You do not need to with-hold any of your medications but let the doctor know if you are on anticoagulants such as warfarin, dabigatran or rivaroxaban.

• Tell your neurologist if you have a cardiac defibrillator or pacemaker.

It takes up to 30 minutes depending on the condition being tested.

1. If you are asked to remove clothing, you will be given a gown to wear.

2. You will be asked to lie down on a bed for the test.

3. The neurologist will locate the nerve(s) to be studied. They will attach a recording electrode to the skin over your nerve, using a special paste and then place a stimulating electrode away from the recording electrode, at a known distance.

4. A mild and brief electrical shock, given through the stimulating electrode, will stimulate your nerve.

5. You may experience minor discomfort for a few seconds.

6. The stimulation of the nerve and the response will be displayed on a monitor

7. Afterwards, the paste used to attach the electrodes will be removed from your skin.
   
   You may return to your usual activities straight away. A copy of the report from the study will be sent through to the referring doctor within 24-48 hours of the study being completed.