Electrophysiologic tests provide information about the nerves and muscles of the spine, and probe for the effects of disease on neuromuscular function of the spine. Their purpose is to identify a neurologic deficit that can explain a patients pain.
The spinal cord and nerves run the length of the spine behind the vertebral bodies and discs. The spinal nerves pass out of the spine into the arms from the cervical region, to the chest and abdominal wall from the thoracic region, and into the legs from the lumbosacral region of the spine. Three electrodiagnostic tests are available to examine the spinal cord, its nerves, and its muscles: electromyography (EMG), nerve conduction studies (NCS), and somatosensory evoked potentials (SSEP) testing.
Electromyography tests the functions of the peripheral nerves and the way that the nerves affect muscle function. During an EMG study, fine needle electrodes (like accupuncture needles) are placed into muscles of the arms and/or legs being tested and along the muscles surrounding the spine. Sometimes skin surface electrodes are used. The nerve is stimulated nearer the spine and impulses are recorded from the muscle electrodes. Muscle twitching and contraction is felt by the patient; some patients report a level of discomfort with this test. EMG testing may be used to diagnose a pinched nerve in the spine (radiculopathy), and can also be used to differentiate radiculopathy from other causes of arm and/or leg pain such as peripheral neuropathy (primary disease of the nerve endings, most commonly seen in patients with diabetes) and peripheral entrapment neuropathy (a pinched nerve outside of the spine such as carpal tunnel syndrome).
Nerve conduction studies make use of the nerves ability to conduct an electrical signal. A nerve is stimulated by an electrical signal from a skin electrode placed over the nerve, and a transmitted signal is recorded at a selected site by another skin electrode somewhere along the same nerve. If the signal travels normally, the nerve is healthy. Often more than one nerve is tested. In NCS tests, the patient will feel an electrical impulse; muscles may twitch. The patients role is passive, to relax as much as possible.
Somatosensory evoked potentials are of most use when there is the suspicion of spinal cord dysfunction, whereas NCV and EMG testing assess the neuromuscular system outside the spinal cord. Evoked potentials are tiny electrical signals recorded from the spine and head following stimulation of nerves in the limbs or brain.
These tests, typically in combination, tell the physician if there is demonstrable dysfunction of the nervous system below the brain. They are often able to localize at what level that dysfunction is occurring and how severe the dysfunction is. They may also be able to provide some information about the likelihood of neurologic recovery with treatment.
Electrodiagnostic (EDX) studies (sometimes called EMG for electromyography) are a commonly used technique to test the function of muscles and nerves. These studies are ordered by physicians to help determine the cause of back or neck pain, numbness/tingling and strength loss. Commonly diagnosed conditions include “pinched nerves” (radiculopathies), peripheral nerve injuries and muscle disease.
They are usually two parts: one testing nerves (referred to as “nerve conduction studies”) and the other testing muscles (referred to as “electromyography”). These studies allow the NASS physician to learn how nerve and muscles are functioning. This testing process often helps to narrow down the possible causes of back/body pain and muscle weakness.
Nerve conduction studies
It is done by placing sensors over nerves in the arms and legs and then stimulating those nerves with small electric sensations. Most patients report that these studies are “uncomfortable” but not necessarily painful. The doctor is able to see how fast or slow nerves are functioning. Comparisons are made to averages to see if see the nerves are working properly.
EMG is performed by placing small needles in the muscles of the arm, leg or back to directly evaluate the electrical activity caused by a muscle contraction. Most patients state that the needles feel like a small cramp or a splinter in the muscle. EMG allows the NASS physician to evaluate how well muscles are functioning. In addition, the EMG study can help determine if muscles are receiving the proper signal from nerves.
When would my NASS doctor consider an electrodiagnostic study?
This study is considered when the reason for pain or tingling or weakness is not clear. This study can also be used to determine the severity of a nerve injury or how badly a nerve is being pinched in the neck or back. Occasionally other conditions can mimick a pinched nerve in the back or neck. Electrodiagnostic studies can also help determine if other conditions are occurring.
What should my NASS doctor know about me to determine if I should have an EDX?
The doctor performing the electrodiagnostic test will ask questions about the nature of your pain, tingling and weakness. This will help them determine which nerves and muscles to test. The NASS physician may also ask questions about other conditions which may affect the nerves and muscles, such as diabetes and thyroid problems. Your NASS doctor should know if you have ever had a neck or back surgery.
Are there any reasons I should not have an EDX study?
If you are on blood thinning medications, such as aspirin, plavix, heparin or warfarin (Coumadin), the NASS physician may not perform certain portions of the test. If that information is absolutely necessary, you may be asked to stop blood thinning medication prior to the electrodiagnostic test. If you have a pacemaker or similar device, certain portions of the test may not be able to performed.