What are electromyogram (EMG) and nerve conduction studies?
An electromyogram (EMG) measures the electrical activity of your muscles when you are not using them (at rest) and when you tighten them (muscle contraction).
Nerve conduction studies (NCS) measure how well and how fast the nerves can send electrical signals.
EMG and nerve conduction studies are often done together. If they are done together, the nerve conduction studies are done before the EMG.
Why are electromyogram (EMG) and nerve conduction studies done?
You may need an EMG to find diseases that damage your muscles or nerves or to find out why you can't move your muscles (paralysis), why they feel weak, or why they twitch. These problems may include a herniated disc, amyotrophic lateral sclerosis (ALS), or myasthenia gravis (MG).
You may need nerve conduction studies to find damage to the nerves that connect the brain and spinal cord to the rest of the body. (This is called the peripheral nervous system.) These studies are often used to help find nerve disorders, such as carpal tunnel syndrome.
How are electromyogram (EMG) and nerve conduction studies done?
You lie on a table or bed or sit in a reclining chair so your muscles are relaxed.
For an EMG:
- Your doctor will insert a needle electrode into a muscle. This will record the electrical activity while the muscle is at rest.
- Your doctor will ask you to tighten the same muscle slowly and steadily while the electrical activity is recorded.
- Your doctor may move the electrode to a different area of the muscle or a different muscle.
For nerve conduction studies:
- Your doctor will attach two types of electrodes to your skin.
- One type of electrode is placed over a nerve and will give the nerve an electrical pulse.
- The other type of electrode is placed over the muscle that the nerve controls. It will record how long it takes the muscle to react to the electrical pulse.
How do you prepare for your child's electromyogram (EMG) and nerve conduction studies?
- Tell your doctors ALL the medicines, vitamins, supplements, and herbal remedies your child takes. Some medicines can affect the test results. You may need to stop giving your child some medicines before these tests.
- Have your child wear loose-fitting clothing. He or she may be given a hospital gown to wear.
- The electrodes for the test are attached to your child's skin. The skin needs to be clean and free of sprays, oils, creams, and lotions.
What do the results of electromyogram (EMG) and nerve conduction studies mean?
Your doctor may be able to tell you some of the results of your nerve studies right after the tests. A full report may take 2 to 3 days.
Normal: | The EMG recording shows no electrical activity when the muscle is at rest. There is a smooth, wavy line on the recording with each muscle contraction. The nerve conduction studies show that the nerves send electrical impulses to the muscles or along the sensory nerves at normal speeds, or conduction velocities. Sensory nerves allow the brain to feel pain, touch, temperature, and vibration. Not all nerves have the same normal conduction velocities. They generally get slower as a person gets older. |
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Abnormal: | For an EMG, electrical activity in a muscle at rest shows that there may be a problem with the nerves used by the muscle. Abnormal wave lines when a muscle contracts may mean there is a muscle or nerve problem. Examples include a herniated disc, amyotrophic lateral sclerosis (ALS), and inflammation. In nerve conduction studies, the speed of nerve impulses is slower than normal for that nerve. Slower speeds may be caused by injury to a nerve or group of nerves. |
The results from these studies are looked at along with other things. These include your medical history, symptoms, physical and neurological exams, and the results of other tests. All of these things may help your doctor find the problem or see how a disease is changing.
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