Nerve Conduction Study

A medical diagnostic tool used to evaluate the ability of the motor and sensory nerves for electrical conduction is the Nerve conduction study. Nerve conduction studies are performed by medical specialists in neurophysiology, physiatry and neurology with sub-specialization in electro diagnostic medicine. The common measurement made during this test is called Nerve conduction velocity or NCV. This is conducted to determine the damage and destruction caused to nerves.

Procedure

The procedure is to stimulate the nerve with surface electrode patches attached to the skin. Two electrodes are placed on the skin over the nerve. One electrode stimulates the nerve with a mild electrical impulse. The resulting electrical activity is recorded by another electrode. This testing is repeated in about 2 - 3 places along the arms or legs. After the procedure, the nerve conduction speed is calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.

The nerve conduction velocity (speed) is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.

A related procedure that may be performed is electromyography (EMG). An EMG measures the electrical activity in muscles and is often performed at the same time as NCS. Both procedures help to detect the presence, location and extent of diseases that damage the nerves and muscles.

Prior to the procedure

This study does not require any fasting or sedation prior to the procedure. But body temperature must be maintained before and during the procedure as low body temperature slows nerve conduction. Keep the doctor informed in case of any medicine or herbal supplements you might be taking. You must stop using lotions or oils on your skin a few days before the procedure. Based on your medical condition, the doctor may request any other specific preparation.

During the procedure

A nerve conduction study is performed as an outpatient procedure although procedures may vary depending upon the condition and doctor's practices. The study is performed by a neurologist although a technologist may perform portions of the test. During the procedure, the patient is asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or any other metal objects that may interfere with the procedure.

The patient is asked to either sit or lie down for the test. A recording electrode is attached to the skin over the nerve with a special paste. A stimulating electrode is placed at a known distance away from the recording electrode. The nerve is stimulated by a mild and brief electrical shock through the stimulating electrode. You might experience minor discomfort for a few seconds. The patient senses rapid tingling in the area. The stimulation of the nerve and the response are displayed on an oscilloscope.

What does the test results indicate?

Generally, the nerve conduction velocity would be around 50 to 60 meters per second. But it tends to vary from person to person and from one nerve to another.

The speed of the nerve conduction study is related to the diameter of the nerve and the degree of myelin sheath (which is a type of insulation) around the nerve. While a normally functioning nerve will transmit a stronger and faster signal, a damaged nerve will be slower. The larger the wire, the better the insulation and more consistent and stronger will be the signal.

If results are abnormal, they may be due to some sort of neuropathy or damage to the nerve resulting from a traumatic injury or nerve. Sometimes, other diseases may also cause the impulses to slow down. It could be due to conduction block that is an obstacle to the impulse within the nerve or due to demyelination or damage to the myelin sheath.

Why nerve conduction study?

Nerve conduction study is done along with EMG to differentiate a nerve disorder from a muscle disorder. While nerve conduction study detects whether the nerve has any problem, EMG detects whether a muscle is functioning properly in response to the nerve's stimulus. Whenever there is any neurologic injury or disorder, nerve conduction studies often combined with needle electromyography measure are used. This helps in identifying cause for any pain or weakness in the limbs from spinal nerve compression or injury.

Nerve conduction studies are used primarily for evaluation of numbness, tingling and burning or weakness of arms and legs depending upon the part of the body the symptom is present. Physical examination by the doctor and patient's history help to direct the investigation. A number of disorders are diagnosed by nerve conduction studies - carpal tunnel syndrome, Gullian-Barre syndrome, peripheral neuropathy, spinal disc herniation, ulnar neuropathy and others.

Risks of the procedure

Although the voltage of electrical pulses used in this study is quite low, there may be risks depending upon specific medical conditions. Certain factors such as damage to the spinal cord, severe pain before the test and body temperature may affect the test. In case you are using cardiac defibrillator or pacemaker, adequate precautions need to be taken.