Nerve Conduction Study (NCS) and Electromyography (EMG)
Nerve conduction studies (NCS) measure how well and how fast nerves can send electrical impulses. An electromyogram (EMG) measures the electrical activity of muscles both at rest and during contraction.
The test is based on placing needles into the arm or leg and measuring the length of time required for an electrical signal to pass down the nerve root.
Muscles cannot contract well if they do not have full nerve flow, and this may limit your ability to function normally. Back and neck NCS/EMG studies help identify why a muscle may be weak and where a nerve blockage may be occurring.
Nerve conduction studies are most commonly performed for conditions that cause symptoms in the arms or legs. Some of the more common diagnoses include radicular symptoms, herniated disc, stenosis and nerve root compression.
Testing can also evaluate for non-spinal causes of limb pain and weakness such as carpal tunnel syndrome and peripheral neuropathy.
- Inform your doctor if you have a pacemaker or other implanted stimulator or in-dwelling catheter (these may not prevent the study, but certain precautions will be taken).
- Do not eat or drink anything that contains caffeine or smoke for three hours before the back or neck NCS/EMG.
- Wear loose clothing as testing will include the neck and arm or the leg and lower back.
- Do not apply lotion to the extremities on the day of testing.
The procedure will usually be performed in an exam room:
- For the nerve conduction study (NCS):
- Your skin in the area to be tested may be cleaned if needed.
- Multiple electrodes will be attached to your skin.
- You will feel light electrical pulses over the muscles controlled by the nerves being tested.
- For the electromyography (EMG) test:
- Your skin in the area to be tested will be cleaned if needed.
- Micro-needles will be placed into the muscles to be tested.
- Readings will be made with the muscle at rest and again after you contract the muscle.
- The total test time is about one hour (the total time impulses are actually being sent along the nerves is only seconds).
- You will be able to leave the clinic after the test is performed.
- The information about the signals traveling along the nerves will be recorded and read by the physician performing the test. The results will be sent to your treating physician to discuss with you.