Nerve Conduction Studies/Electromyography (NCS or NCV/EMG)
What are nerve conduction studies (NCS)?
Nerve conduction studies (NCS) provide information about how well and how fast the nerves in your body send electrical impulses. This test can be used to check for various types of problems with the peripheral nervous system, which includes all the nerves in your body apart from those in your brain and within the spinal cord itself. Nerves in the brain and spinal cord make up the central nervous system.
How do nerves work?
Nerves are like electrical cables that transmit impulses to allow communication between the brain and all the other parts of the body. These nerves or cables send information from the brain to the tissues of the body and also carry information from the body back to the brain. Peripheral nerves connect the outside of the body to the spinal cord and the spinal cord then transmits signals to and from the brain. The median nerve is an example of a peripheral nerve that runs through the arm into the wrist (carpal tunnel) and is one part of the connection between the thumb and the spinal cord.
What are nerve conduction studies used for?
If nerves are damaged the electrical signal often moves slower through the nerve fiber. By measuring the speed (velocity) and the amount (amplitude or voltage) of the impulse that travels from one point in the nerve to another, NCS allows us to assess:
- The degree of nerve damage following an injury.
- For damage to nerves caused by conditions such as diabetes.
- For conditions affecting the nervous system.
- 'Trapped' nerves - conditions such as carpal tunnel syndrome.
How do nerve conduction studies work?
Small electrical pulses are delivered to the nerves of the body to mimic the electrical signals made by nerves. Our technician will place electrodes (small devices that detect and supply electricity) against the skin to send impulses from one point along the course of a nerve and record from another point. If the nerve is attached to a muscle, the muscle will contract in response to the electrical signal and this response is measured by the electrodes on the skin. Similarly, to test sensory nerves, the electrodes are usually attached to the fingers or toes with another electrode either at the ankle or wrist. When the electrical pulse is applied to the fingers or toes the sensory nerve carries the electrical signal away from the arm or leg. The electrode at the wrist or ankle detects the electrical impulse when it reaches that point.
Our machine receives the signals from these electrodes and measures the voltage of the response and the time taken for the impulse to travel in the nerve from the first electrode to the second. This information computes the speed at which the impulse is travelling along the nerve. This is referred to as the conduction velocity.
Nerve conduction tests may take from 15 minutes to 1 hour or more, depending on how many nerves and muscles are studied.
What is electromyography?
Electromyography (EMG) is the recording (graphy) of the electrical activity (electro) of your muscles (myo). This is typically an extension of the nerve conduction study whereby a very small needle is inserted into the muscle and we listen and watch the pattern of activity to determine if there is any injury to the nerves connected to the muscle and in some cases we can detect disease in the muscle itself (myopathy). Injury to nerves can manifest as abnormal spontaneous activity in muscles and EMG can give information about nerves being pinched in the neck or low back (usually be slipped discs) and injury or diseases of the nerves themselves such as the extent of damage to the median nerve at the wrist (carpal tunnel syndrome). This information can be very helpful in understanding where and to what degree there is damage to nerves and guide your referring physician’s decisions on further testing and treatment.
What should I do to prepare for an NCS/EMG?
We ask that you not use hand lotion or creams on the day of your test. Loose-fitting clothing that can be rolled up to above the elbows and knees is very helpful. Bracelets, rings and watches will usually be removed for tests on the hands, and socks or tights removed for investigation on the feet.
Are there any possible side-effects or complications?
While it may sound alarming to have an electrical impulse applied to your skin, the amount of electricity that passes through you is very small. Most people tolerate the test very well and have no side-effects or complications after the test.