What is EMG testing?
St. Joseph’s/Candler Neurologist Dr. Jonas Vanags discusses diagnostic tools used to identify a variety of neuromuscular disorders
Did you know our muscles and nerves work hand in hand? Without the help of our nervous system, our voluntary muscles would weaken to the point of uselessness. So when there’s a lack in communication between nerve cells and muscle cells, it can lead to certain neuromuscular disorders, some of which can be life-threatening.
Neurologist Dr. Jonas Vanags treats neuromuscular disorders at St. Joseph’s/Candler Physician Network – Neurology. To diagnose conditions, he uses two common diagnostic tools – nerve conduction studies (NCS) and electromyography (EMG).
“A routine EMG can help diagnose a number of nerve disorders or muscle disorders,” Dr. Vanags says. “The first part of our testing is called a nerve conduction study, in which we put electrodes either over the nerve or over the muscle supplied by the nerve. We use electrical stimulation to record how fast and strong the nerve responds.”
The second part of the testing is the EMG. During the test, your doctor will put a small needle through your skin into a muscle. The electrical activity picked up by the electrodes is then displayed on a monitor in the form of waves.
EMG measures the electrical activity of your muscle during rest, slight contraction and forceful contraction. Muscle tissue does not normally make electrical signals during rest. When an electrode is put in, a brief period of activity can be seen. But after that, there should be no signal. So if your muscle is damaged or has lost input from nerves, it may have abnormal electrical activity during rest.
An EMG may be done to find the cause of symptoms such as muscle weakness, deformities, stiffness, involuntary muscle twitching and shrinkage.
An abnormal EMG result may be the sign of a muscle or nerve disorder such as:
- Focal nerve disorders, such as carpal tunnel syndrome
- Radiculopathy (a nerve root disorder that affects the neck and back)
- Myopathies (muscular disease that is not caused by a defect in the nerves)
- Peripheral neuropathy (damage to peripheral nerves that causes numbness, pain or weakness, usually in hands or feet)
Further testing may be required to diagnose the specific condition. One example is single fiber EMG.
“If I suspect that someone has a disorder of the junction point between the nerve and the muscle, called the neuromuscular junction, I can perform further studies such as the single fiber EMG,” Dr. Vanags says. “This test also uses a tiny needle, but this one is specifically designed with a small port that is the size of microns. We insert this needle into the muscle and position it between two single muscle fibers that share the same nerve supply.”
If both of these single muscle fibers do not fire at the same time, Dr. Vanags can determine whether there is a disorder of the neuromuscular junction. One such condition is myasthenia gravis, a neuromuscular disease in which antibodies caused by an overactive immune system block communication at the neuromuscular junction, leading to weakness of skeletal muscles.
Mild symptoms of myasthenia gravis may include drooping eyelids or double vision. If more severe, it can cause chewing, swallowing and breathing problems and limb weakness. If severe enough, it can be life-threatening, Dr. Vanags says.
“This is not the most comfortable procedure, but the stakes are high, and no other test has the same sensitivity and specificity,” Dr. Vanags says. “With a very strong certainty, the single fiber EMG can rule in or rule out myasthenia gravis better than any other test in the world.”