Electromyography (EMG) and Nerve Conduction Velocity (NCV)
Nerve conduction studies (NCS) and electromyography (EMG) help your child’s doctor see how his nerves and muscles are working. Together, these tests are often called “EMG testing.”
EMG testing can help your child’s medical team diagnose many different neuromuscular and muscular disorders. These tests are also used to check on how your child’s nerves and muscles are functioning later on, after he’s already been diagnosed and gotten treatment.
EMG testing can help diagnose and evaluate a variety of disorders that affect your child’s peripheral nervous system, such as:
- muscular dystrophy
- other myopathiesincluding congenital myopathies, glycogen storage diseases and other metabolic myopathies, polymyositis and dermatomyositis
- neuropathiesincluding Charcot-Marie-Tooth disease, Guillain-Barré syndrome, chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and Friedreich ataxia
- traumatic nerve injuriesincluding accidents and sports injuries
- brachial plexus birth palsy (Erb’s palsy)
- motor neuron diseases(anterior horn cell diseases) including spinal muscular atrophy
- neuromuscular junction disordersincluding myasthenia gravis, congenital myasthenic syndromes and botulism
Nerve conduction studies (NCS)
The first part of the study, NCS, measures how electrical signals travel through your child’s nerves. This part usually takes about 30 to 45 minutes.
A doctor places three electrodes (stickers) on the part of your child’s body being tested (usually his arm or leg). Then the doctor uses a stimulator to send small amounts of electrical current through your child’s nerves. This isn’t painful; it feels like static electricity that you experience in the winter when you walk across a carpet and touch a metal doorknob. The electrodes record how strongly and quickly signals travel through your child’s nerves. This measurement is called nerve conduction velocity (NCV).
The second part of the study, electromyography (EMG), records the signals that are moving through your child’s muscles. The information from the test is called an electromyogram. An EMG usually takes no more than 15 minutes.
A doctor places a very thin needle electrode (similar in size to the needles used in acupuncture) into one or more of your child’s muscles. When this happens, your child will feel a tiny pinch. Then the doctor takes recordings while the muscle is at rest and, if possible, while your child moves the muscle. Your child will not receive any electrical stimulus through the needle; it’s just a measuring device.
This part of the study is sometimes uncomfortable, so our doctors always try to balance the need for information with the comfort of your child. If your child becomes really uncomfortable, your doctor may decide to stop the study early.
We often describe the EMG needle as a “microphone,” because we actually listen to the sound of the electrical signal through speakers. Many children become intrigued by the crackling noise. In fact, children often offer their ideas about what their muscles sound like—such as rain on a roof, a lobster boat or a motorcycle. Most children tolerate the study without too much trouble, especially with their parents in the lab with them.
In some cases, we perform specialized forms of EMG testing in order to answer specific questions your child’s doctor may have. These specialized tests may make the study take slightly longer than the usual timeframe of one hour.
One specialized test we perform is single-fiber EMG, a test that can help diagnose a condition called myasthenia gravis.
If your child needs an extended version of these tests, we may perform her EMG in our Day Surgery Unit using general anesthesia.
Q: Is EMG testing painful?
A:The stimuli in nerve conduction studies (NCS) feel like static electricity (like when you walk across a carpet and touch a metal doorknob). The electromyography (EMG) portion of the test may be a bit painful for some children. But many children become distracted by the crackling sound of their muscles’ electrical activity and are able to tolerate the study without too much difficulty.
Q: What kind of information does the study give?
A:These tests help your child’s doctor see how his nerves and muscles are working. NCS measures how electrical signals travel through the nerves, and EMG records the signals moving through the muscles. This information can help your child’s doctor diagnose many different neuromuscular and muscular disorders.
Q: Can my child be sedated?
A:In most cases, we can perform this test more quickly and get better information if your child is not sedated or under anesthesia. Fortunately, most children tolerate the study well. All of our doctors and technologists work hard to help your child understand the test and comfort him. Having you there with him helps a lot, too.
Occasionally, when we feel we’ll get better information using general anesthesia, we may schedule your child’s EMG testing in our Day Surgery Unit. On rare occasions in which a child comes to the EMG laboratory but can’t tolerate the study (such as for some very young children), we may reschedule it in the Day Surgery Unit so it can be done under general anesthesia. General anesthesia is associated with a small risk of complications, which is why we don’t use it on a routine basis for this study.
Q: Will my child miss school as a result of this study?
A:The test usually only takes an hour, and most children return to school the same day. Some parents prefer to keep their child home for the rest of the day, depending on factors such as the child’s age. All children should be ready to return to school by the next day.
Q: Does the test cause any nerve damage?
A:No, the electrical stimuli of NCS do not cause nerve damage. The needle electrodes used for EMG are not placed near any major nerves.
Q: Can any other tests substitute for EMG?
A:If your doctor thinks that your child may have a muscle disorder, genetic testing may be enough to make the diagnosis. However, when the diagnosis is unclear, an EMG can help determine whether the nerves or muscles aren’t functioning normally. In some cases, a muscle biopsy or other test may be needed to provide a full diagnosis.
Questions to ask your doctor
If your child is going to be having EMG testing, you and your child probably have a lot of questions on your mind. What do the tests involve? Are the electrodes going to hurt my child? In these pages we’ve tried to provide some answers to questions you may have, and you should feel free to ask your child’s doctor about the tests, too.
At a medical appointment, it can be easy to forget the questions you wanted to ask. It’s often helpful to jot them down ahead of time so that you can get the information you need and feel comfortable with the plan for your child’s testing. If your child is old enough, you may want to suggest that he write down what he wants to ask his doctor, too.
Some of the questions you may want to ask include:
- What will happen during the EMG testing?
- Is there anything we need to do to get ready?
- Will my child be able to go to back to school that day?
- How is this test going to help in diagnosing my child’s condition?
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|Muscles in action|
This interactive feature lets you explore the anatomy of a muscle, how it contracts and what happens in some neuromuscular disorders.