Electromyogram and Nerve Conduction Studies
An Electromyogram (EMG) is a diagnostic test that measures the electrical activity of your muscles. It is performed in conjunction with a Nerve Conduction Study (NCS). It is typically performed when there are symptoms of numbness, tingling, radiating pain, muscle weakness, or difficulty with coordination. Together, the EMG and the NCS studies can detect certain nerve and muscle disorders. They are performed by either Neurologists or Physiatrists (doctors who specialize in Physical Medicine and Rehabilitation).
Dr. Miller routinely performs these tests to help diagnose conditions such as radiculopathy (“pinched nerve”), spinal stenosis, peripheral nerve damage, compression neuropathies (i.e. Carpal Tunnel Syndrome), or less commonly, neuromuscular disorders. The study in its entirety typically lasts 45-60 minutes.
Nerve Conduction Study (NCS)
THEORY: Nerves are somewhat akin to electrical wires, as they transmit signals from the brain and spinal cord to the peripheral skeletal muscles. The speed and number of nerve fibers are evaluated in this section of the test.
PRACTICAL NCS: The doctor who is performing the study will first make marks with measurements and landmarks on the skin which can be easily removed later with soap and water. A recording electrode, made of a small metal disk or sticker, is placed on the fingers or foot. A stimulator is placed at the measured mark and when activated, the recorder displays an image on the computer screen. The waveform is then analyzed for its speed and shape.
Most patients do not find this portion of the test uncomfortable. The activation of the stimulator has been likened to the feeling of static electricity as when a person rubs his feet on a carpet and then touches another person. If pain is experienced, it will not be continuous and will last a very short time, less than a second. More importantly, the applied electric stimulus has never been found to cause any nerve or muscle damage.
THEORY: Normal muscle has certain characteristic sounds and waveforms when it is at rest and when it is being activated.
PRACTICAL EMG: A small pin, akin to an acupuncture needle, is placed into the muscle and the examiner listens to the sounds of that muscle at rest and during activation of the muscle, as well as sees a waveform on a monitor called an oscilloscope . Therefore, the first aspect of this section asks the patient to relax as the physician places the pin into different parts of the muscle, sampling different sections for normal or abnormal activity. The spontaneous activity of the muscle sounds like a “pop” and “snap” sound, much like popcorn in the microwave. In the second part of the test, the patient is asked to contract the muscle, for example, by bending or lifting the hand or leg. The examiner will observe the action potential (the frequency, the shape, and timed response of the motor unit) on the monitor and this will provide information on how the nerves and muscles are working together. Multiple muscles are examined for proper diagnostic information to be collected.
Most patients do not find this portion of the test painful, but it may be slightly uncomfortable. In most cases, the pin placement into the muscle will not cause bleeding. However, just as immunizations or a medication shot can cause bleeding, it can be controlled with pressure from the physician’s hand and cotton pad. Similarly, as with the NCS, this part of the test has never been found to cause any nerve or muscle damage. Disposable needles are used for each new patient and are immediately disposed of following use, so there is no risk of contracting an infection from another person.
Other Helpful Information Before The EMG/NCS:
- Avoid applying any creams or oils prior to coming to your appointment. It is important that the skin is cleaned with soap and water, free from lotions, in order to maximize adherence of the electrodes to the skin.
- If you feel that you may be sensitive to the pain, you can take a Tylenol, anti-inflammatory, or any other pain pill that your doctor has already prescribed to you prior to the appointment, as such medication will not affect the efficacy of the test. Just be sure to have someone drive you, as the pain pill may affect your sensorium.
- If you are on anticoagulation or blood thinners or if you have a pacemaker or implanted defibrillators, you should notify the physician performing the test, but generally this is not a contraindication. If you have a joint replacement or other artificial components in your body, you do not need to take antibiotics specifically for the EMG. You ought take your usual medication on the day of the test. No special preparation is necessary.
- If for any reason you feel that you cannot continue with the study, do not hesitate to tell the examiner to stop. If you have tolerated at least some of the test, then that information may still provide valuable information for the examiner.