Electromyography (also called EMG or Myogram)
EMG tests, also known as electromyography or myogram, are designed to tests the activity of skeletal muscles in the legs that are supplied with information from the nerve roots of the lower lumbar area of the spine. the doctors test the activity of the muscles by inserting electrodes directly into the leg muscles, or with surface sensors that are placed on the skin. to observe and record this muscle activity, the sensors are connected to a machine called an oscilloscope which includes a screen where the signal activity from the muscles can be observed. During the EMG test, doctors can observe the muscle activity during rest, when they ask the patients to flex the muscle, and when the muscle is electrically activated. The shape, size, and presence of the waved produced on the screen may present as decreased activity than normal if the patient has damage to the nerves of the lumbar spine or the nerve roots exiting the spine. The patient may experience some discomfort or pain during the test because of the placement of the needle into the muscle, and in rare cases feel moderate to severe pain afterwards to the area of the skin and muscle being punctured by the needle. Just in case, patients may take over the counter analgesics, such as acetaminophen or aspirin, with them to the tests in case they experience pain afterwards. For patients that are already on back pain medications, they should consult with their doctor beforehand as to the appropriate dose of current or new medications to take after the test if they feel some level of discomfort.
The purpose of the myogram is to determine if the cause of pain or sensation loss in the legs is caused by compression of the spinal nerve roots. If problems with the spinal nerve roots are involved, then the results of the EMG tests may indicate which spinal nerve roots are involved. EMG tests will probably not be ordered for back problems such as osteoarthritis of the spine, there the symptoms of back pain are restricted to the lower back alone.
EMG tests may be recommended for patients with back pain when nerve root compression is suspected, but it is unknown which nerve root is being compressed. When the nerves are compressed for a significant period of time (three weeks or longer) the muscles supplied with information by the nerve will begin to contract spontaneously. Also, continued compression of that nerve will cause slowed down electrical conduction along that nerve. The EMG tests are designed to test the electrical conduction of these nerves and muscles supplied with information by the nerve roots of the spine. Electromyography tests may also be helpful at distinguishing between different type of nerve conduction problems, such as radiculopathy (nerve root compression) and nerve degeneration (neuropathy). These tests are usually designed to supplement the information provided to the back pain specialist, they are not highly reliable alone in determining the specific nerve root being compressed.
EMG tests are sued for identifying neuromuscular diseases such as bruxism, periodic leg movement disorder, and inflammatory muscle disorders such as rhabdomyolysis.