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Specialized tests target source of muscle and nerve pain
Many people suffer from acute and/or chronic nerve and muscle pain. This pain can be felt as an ache in muscles or shooting pain. There may be an unexplained weakness in the arms and legs and/or numbness and tingling in one or more areas of the body. The painful, aching sensations may be caused by diseased or injured nerves or muscles.
Some common pain-inducing conditions include carpal tunnel syndrome, pinched nerves in the neck or back and peripheral neuropathy (caused by various conditions such as diabetes) – just to name a few. In cases where the cause and/or origin of the pain is unclear, electrodiagnostic testing can provide valuable information to physicians. Individuals with general nerve and muscle problems – including pain, weakness, numbness and tingling – can benefit from these targeted tests performed in specially equipped electrodiagnostic labs.
The purpose of electrodiagnostic testing is to help physicians figure out whether the symptoms are caused by a problem in the nervous system and, if so, where the problem is occurring and the severity of the injury or disease.
Ledington clarifies that while this test does not detect pain, it is useful for determining if there is an underlying neuropathic condition that may be causing pain or other symptoms.
EMGs help diagnose three kinds of diseases that interfere with normal muscle contraction:
- Diseases of the muscle itself
- Diseases of the neuromuscular junction, which is the connection between a nerve fiber and the muscle it supplies.
- Diseases “upstream” in nerves and nerve roots, which can be caused by either nerve damage or ongoing nerve injury
The nerve conduction study is most often done first. In this part of the test, several electrodes are attached to the surface of the skin atop a specific muscle or sensory nerve distribution. The nerves are then stimulated by electrical impulses and the responses recorded over the muscle or sensory nerve ending. Information can then be gathered about the function of the nerves.
“Nerve conduction studies help determine how fast or how slow the nerve is conducting impulses, how much information the nerve is carrying and whether or not there is blockage of the impulse at certain sites,” Ledington said. “This gives valuable information about nerve function and what components of the nerve may be affected. It can also give information on the severity or prognosis of a nerve injury.”
The second part of the test, called electromyography or simply EMG, assesses muscle function. A muscle contracts when it is stimulated by signals from nerve cells called motor neurons. This stimulation causes electrical activity in the muscle that causes the muscle to contract or tighten. The muscle contraction itself produces electrical signals.
Ledington explains the procedure: “A very fine needle, about the size of a small acupuncture needle, is inserted into a muscle. The muscle is then assessed at rest (relaxed) and then during a contraction. The signal from the muscle is then transmitted from the needle electrode through a wire or wirelessly to a receiver/amplifier, which is connected to a device that displays a readout. The results are either printed on a paper strip or, more commonly, on a computer screen.
“In severe nerve injuries or in certain muscle diseases, the abnormal electrical activity can be seen when the muscle is at rest. When the muscle is contracted, groupings of muscle fibers are seen as waveforms on the computer screen. Information can be gained about muscle function, such as whether there has been remote or chronic nerve injury that has healed, ongoing nerve injury or other muscle disorders.”
An EMG test is a very low-risk procedure and can even be performed in individuals with pacemakers, with appropriate precautions. Some patients report feeling some aching or soreness in the area that has been tested. The soreness usually doesn’t last long and typically can be relieved with over-the-counter pain medications such as ibuprofen or Tylenol. Occasionally there may be bruising or swelling at the needle insertion sites.
Results are usually available immediately, but a trained medical specialist (such as a physiatrist or neurologist) is needed to analyze and interpret them in the context of the patient’s symptoms.
Dr. John Ledington, is a physician at Northern Arizona Orthopaedics’ Spine and Pain Center.