What is EMG and NCV?
Electromyography (EMG) and nerve conduction velocity (NCV) are common tests used to evaluate how nerves and muscles are functioning. NCV measures how fast electrical signals move through a nerve, and EMG records the signals moving through the muscles. Together, these tests are often called “EMG testing” or “Electrodiagnosis and Neurodiagnostics”.
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 body. They allow you to receive sensory information (like how an object feels when you touch it) and control your muscles.
How are the tests performed?
In nerve conduction velocity (NCV), a Dr. Kaster places three surface electrodes on your skin over a targeted nerve. He then emits a mild electrical current through one of the electrodes, which stimulates the nerve. These feel like static electricity that you experience in the winter. This part of the test usually takes 30 to 45 minutes.
The nerve’s resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to determine the speed of the nerve signals.
The NCV test is followed by electromyography (EMG). In this test, a Dr. Kaster places a very thin needle electrode (similar in size to the needles used in acupuncture) into one or more of your muscles. You’re then asked to contract that muscle while Dr. Kaster takes recordings of the electrical activity in the muscle. This part of the test usually takes no more than 15 minutes.
Why the Test is Performed?
The purpose of nerve conduction studies are for the evaluation of paresthesias (numbness, tingling, burning) and/or weakness of the arms and legs. The type of study required is dependent in part by the symptoms presented. A physical exam and thorough history also help to direct the investigation.
Most often, abnormal results are due to some sort of nerve damage or destruction, including:
- Axonopathy (damage to the long portion of the nerve cell)
- Conduction block (the impulse is blocked somewhere along the nerve pathway)
- Demyelination (damage and loss of the fatty insulation surrounding the nerve cell)
Some of the common disorders that can be diagnosed by nerve conduction studies are:
Peripheral neuropathy- Any peripheral neuropathy can cause abnormal results, as can damage to the spinal cord and disk herniation (herniated nucleus pulposus) with nerve root compression.
- Guillain-Barré syndrome
- Facioscapulohumeral muscular dystrophy
- Spinal disc herniation
- Cubital Tunnel Syndrome
- Tarsal Tunnel Syndrome
- Guyon Canal Syndrome
- Peroneal neuropathy
- Alcoholic neuropathy
- Diabetic neuropathy
- Nerve effects of uremia (from kidney failure)
- Traumatic injury to a nerve
- Foot drop
- Carpal tunnel syndrome
- Brachial plexopathy
- Charcot-Marie-Tooth disease (hereditary)
- Chronic inflammatory polyneuropathy
- Common peroneal nerve dysfunction
- Distal median nerve dysfunction
- Femoral nerve dysfunction
- Friedreich’s ataxia
- General paresis
- Mononeuritis multiplex
- Primary amyloidosis
- Radial nerve dysfunction
- Sciatic nerve dysfunction
- Secondary systemic amyloidosis
- Sensorimotor polyneuropathy
- Tibial nerve dysfunction
- Ulnar nerve dysfunction/neuropathy
There are no risks.
An NCV test shows the condition of the best surviving nerve fibers, so in some cases the results may be normal even if there is nerve damage.