What is a Nerve Conduction Study?
A nerve conduction study is also called a nerve conduction velocity test. A nerve conduction study is a test to determine if a nerve is functioning normally. It is often done along with electromyography (EMG).
The nerve conduction study stimulates specific nerves and records their ability to transmit the impulse. Nerve conduction speeds (velocities) tend to decrease with age. Slower conduction velocities may also be caused by injury or damage to a nerve. Therefore, if the nerve is damaged the signal will be slower and weaker. Stimulating the nerve at various places can reveal the specific site of a nerve injury.
Who Needs a Nerve Conduction Study?
This test is used to diagnose nerve damage or destruction. Nerve conduction studies also may be used during treatment to assess progress.
Any person who has, or is suspected of having, a neuropathy is a potential candidate for a nerve conduction study. This includes conditions like:
- Ulnar nerve entrapment (also called cubital/ulnar tunnel syndrome)
- Carpal tunnel syndrome
- Cervical radiculopathy
- Thoracic outlet syndrome
How is a Nerve Conduction Study Performed?
A nerve conduction study is usually performed as an outpatient procedure. Depending upon the amount of nerves to be studied, testing takes 15 minutes to more than an hour. Normal body temperature must be maintained because low body temperature slows nerve signals. Tell your doctor if you have a cardiac defibrillator or pacemaker before the procedure.
First, electrodes are placed on the skin at various locations along the nerve pathway.
Next, an electrode will stimulate the nerve with an electrical impulse. The impulse is brief (a fraction of a second) and contains a very low amount electrical current. The stimulus may be uncomfortable or feel like a static shock that occurs when you touch a doorknob.
Following the stimulation, the nerve's activity is assessed. The other electrodes along the nerve pathway record the time it takes for electrical impulses to travel between them. The speed of the nerve signals is calculated using the distance between electrodes and the time it takes the impulses to travel between them.
For comparison, the corresponding nerves on the opposite side of the body may be studied. Signals can travel at up to 120 miles per hour in healthy nerves. However, signals will travel slower and be weaker in damaged nerves.
What Can the Results of a Nerve Conduction Study Reveal?
Abnormal results occur when signals travel slower along the nerve and/or the signals are weaker, most often this is due to nerve damage. Nerve damage can be the result of conditions like peripheral neuropathies (e.g., carpal tunnel syndrome), spinal cord injury, demyelination, axonopathy and herniated discs that compress nerves.