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A nerve conduction study is usually done along with electromyography (EMG). The nerve conduction study stimulates specific nerves and records their ability to send the impulse to the muscle. The study can show where there is a blockage of the nerve pathway.
Nerve conduction studies are done to:
- Find and evaluate damage to all the nerves that lead away from the brain and spinal cord to the smaller nerves that branch out from them
- Help diagnose nerve disorders, such as carpal tunnel syndrome or Guillain-Barré syndrome
- Find the location of abnormal sensations, such as numbness, tingling or pain
In a nerve conduction study, several flat metal disc electrodes are taped or pasted to your skin. A shock-emitting electrode is placed directly over the nerve to be studied. A recording electrode is placed over the muscles supplied by that nerve. Several, brief electrical pulses are sent to the nerve. You will feel a brief, burning pain, a tingling sensation and a twitching of the muscle when the electrical pulse is applied. It feels like the tingling you feel when you rub your feet on the carpet then touch a metal object. The testing can be quite uncomfortable and makes some people nervous. Keep in mind that only a very low-voltage electrical current is used. Each pulse is very brief (less than a millisecond).
The time it takes the muscle to contract in response to the electrical pulse is recorded. The speed of the response is called the conduction velocity. The corresponding nerves on the other side of the body may be studied for comparison.
Nerve conduction studies are usually done before an EMG if both tests are being done. Nerve conduction testing takes 15 minutes to an hour or more, depending upon how many areas are studied.
Nerve conduction studies show whether the nerves transmit electrical impulses to the muscles or up the sensory nerves at normal speeds (conduction velocities). Sensory nerves allow the brain to respond to pain, touch, temperature and vibration. Different nerves have different normal conduction velocities. Nerve conduction velocities also tend to decrease as a person gets older. Slower conduction velocities may also be caused by injury or damage to a nerve (such as carpal tunnel syndrome) or group of nerves (such as Guillain-Barré syndrome or post-polio syndrome).