Electromyography and Nerve Conduction Velocity

All of our nerves and muscles use electricity to get things done. In fact, you can think of your body as a machine with incredibly intricate wiring. To be sure, it’s more complex than any wiring system that an electrician would design. But — just as an electrician would do if some part of a machine wasn’t working as it usually does — a doctor can test how your child’s nerves and muscles are conducting electricity.

Nerve conduction studies (NCS) and electromyography (EMG) are specific tests that 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. Together, these tests are often called “EMG testing.”

The nerves tested in nerve conduction studies are called “peripheral nerves.” They’re the nerves outside of the brain and spinal cord carrying messages throughout your child’s body. They allow your child to receive sensory information (like how an object feels when he touches it) and control his muscles.

EMG testing can help your child’s doctor diagnose many different neuromuscular and muscular disorders. It’s 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.

Here is some basic information about how the test works:

• In nerve conduction studies (NCS), a doctor places three electrodes (stickers) on the part of your child’s body being tested, then sends small amounts of electrical current through your child’s nerves. These feel like static electricity that you experience in the winter. This part of the test usually takes 30 to 45 minutes.
• In electromyography (EMG), 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, and then takes recordings of the electrical activity in the muscle. This part of the test usually takes no more than 15 minutes.
• EMG is sometimes uncomfortable, but children are usually able to tolerate it well.
• On rare occasions, the test is done with general anesthesia.
• Most children are able to go back to school the same day.

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 (MD)
• Other myopathies including congenital myopathies, glycogen storage diseases, and other metabolic myopathies, polymyositis, and dermatomyositis
• Neuropathies including Charcot-Marie-Tooth disease, Guillain Barre Syndrome, chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), and Friedreich ataxia
• Traumatic nerve injuries including accidents and sports injuries
• Brachial plexus birth palsy (Erb’s palsy)
• Motor neuron diseases (anterior horn cell diseases) including spinal muscular atrophy
• Neuromuscular junction disorders including myasthenia gravis, congenital myasthenic syndromes, and botulism

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.

Our EMG laboratory is just for kids. That means that all of our physicians and technologists are experienced in working with children, making them as comfortable as possible and putting them at ease during what can otherwise seem like a scary test. The lab is staffed by neurologists in our myasthenia gravis, but that’s rarely performed by pediatric specialists.

Visit the Boston Children’s For Patients and Families site to read all about:

• Getting to Boston Children’s
• Accommodations
• Navigating the hospital experience
• Resources that are available for your family

Our EMG laboratory at Boston Children’s Hospital is just for kids. That means that all of our physicians and technologists are experienced in working with children, making them as comfortable as possible during what can otherwise seem like a scary test. Our lab is staffed by neurologists in our Neuromuscular Center.

Founded it 1979, our EMG lab continues to offer the most sophisticated testing possible for our young patients. One of our special capabilities is single-fiber EMG, a specific test that’s useful for diagnosing myasthenia gravis but that’s rarely performed by pediatric specialists.

A feature on the Boston Children's Genetics website explores how tiny freshwater fish are helping researchers develop new therapies for neuromuscular diseases.