What is an electromyogram?
An electromyogram (EMG) is a test that is used to record the electrical activity of muscles. When muscles are active, they produce an electrical current. This current is usually proportional to the level of muscle activity. An EMG is also referred to as a myogram.
EMGs can be used to detect abnormal electrical activity of muscle that can occur in many diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves, peripheral nerve damage (damage to nerves in the arms and legs), amyotrophic lateral sclerosis (ALS), myasthenia gravis, disc herniation, and others.
Why is an EMG test done?
An EMG is often performed when patients have unexplained muscle weakness. The EMG helps to distinguish between muscle conditions in which the problem begins in the muscle and muscle weakness due to nerve disorders. The EMG can also be used to detect true weakness, as opposed to weakness from reduced use because of pain or lack of motivation. EMGs can also be used to isolate the level of nerve irritation or injury.
How is an intramuscular EMG done?
A needle is inserted through the skin into the muscle. The electrical activity is detected by this needle (which serves as an electrode). The activity is displayed visually on an oscilloscope and may also be detected audibly with a speaker.
Since skeletal muscles are often large, several needle electrodes may need to be placed at various locations to obtain an informative EMG.
After placement of the electrode(s), the patient may be asked to contract the muscle (for example, to bend the leg).
The presence, size, and shape of the wave form (the action potential) produced on the oscilloscope provide information about the ability of the muscle to respond to nervous stimulation. Each muscle fiber that contracts produces an action potential. The size of the muscle fiber affects the rate (how frequently an action potential occurs) and the size (the amplitude) of the action potential.
Is an EMG painful?
Yes. There is some discomfort at the time the needle electrodes are inserted. They feel like shots (intramuscular injections), although nothing is injected during an EMG. Afterwards, the muscle may feel a little sore for up to a few days.
How do you prepare for an intramuscular EMG?
For adults, no special preparation is needed. For infants and children, the physical and psychological preparation depends on the child's age, behavior, and prior experience. (For instance, has the child been traumatized by another medical or dental procedure?)
What other test is done during an intramuscular EMG?
A nerve conduction velocity (NCV) test is often done at the same time as an EMG. In this test, the nerve is electrically stimulated while a second electrode detects the electrical impulse 'down-stream' from the first. This is usually done with surface patch electrodes (they are similar to those used for an electrocardiogram) that are placed on the skin over the nerve at various locations. One electrode stimulates the nerve with a very mild electrical impulse. The resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the speed of impulse transmission (nerve conduction velocity). A decreased speed of transmission indicates nerve disease.
The NCV test can be used to detect true nerve disorders (such as neuropathy) or conditions whereby muscles are affected by nerve injury (such as carpal tunnel syndrome). Normal body temperature must be maintained for the NCV test, because low body temperatures slow nerve conduction.
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MS (Multiple Sclerosis) vs. ALS (Amyotrophic Lateral Sclerosis)
ALS (amyotrophic lateral sclerosis, Lou Gehrig's disease) and MS (multiple sclerosis) are both diseases of the nervous system (neurodegenerative). ALS is a disease in which the nerve cells in the body are attacked by the immune system, although it's not considered an autoimmune disease by some scientists. MS is an autoimmune disease in which the insulated covering of the nerves (myelin sheath) in the CNS (central nervous system) degenerate, or deteriorate.
Scientists don't know the exact cause of either problem. However, they have discovered that mutations in the gene that produces the SOD1 enzyme were associated with some cases of familial ALS. Scientists also theorize that multiple sclerosis may be caused by infection or vitamin D deficiency. ALS occurs between 50-70 years of age (the average age of occurrence ALS is 55), and mostly affects men. While MS occurs between 20-60 years of age, and mostly affects women. About 30,000 people in the US have ALS, and an average of 5,000 new diagnoses per year (that's about 15 new cases per week). Worldwide, MS affects more than 2.3 million people, with about 10,000 new cases diagnosed each year (that's about 200 new diagnoses per week).
Some of the signs and symptoms of both diseases include muscle weakness, muscle spasms, problems walking, fatigue, slurred speech, and problems swallowing. ALS signs and symptoms that are different from MS include problems holding the head upright, clumsiness, muscle cramps and twitches, problems holding objects, and uncontrollable periods of laughing or crying. MS signs and symptoms that are different from ALS include vision problems, vertigo and balance problems, sexual problems, memory problems, depression, mood swings, and digestive problems.There is no cure for either disease, however the prognosis and life expectancy are different. Multiple sclerosis is not a fatal condition, while ALS progresses rapidly and leads to death.
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There are many causes of back pain. Pain in the low back can relate to the bony lumbar spine, discs between the vertebrae, ligaments around the spine and discs, spinal cord and nerves, muscles of the low back, internal organs of the pelvis, and abdomen, and the skin covering the lumbar area.
Spinal Fusion
A minimally invasive surgical procedure, the spinal fusion is used to treat lumbar (lower back) pain if the pain hasn't resolved on its own after six to 12 weeks. A spinal fusion operation causes the vertebrae (bones of the spine) in the lower back to grow together, reduce pressure on the nerves, and reduce pain.
Muscle Cramps
Muscle cramps are involuntarily and forcibly contracted muscles that do not relax. Extremely common, any muscles that have voluntary control, including some organs, are subject to cramp. Since there is such variety in the types of muscle cramps that can occur, many causes and preventative medications are known. Stretching is the most common way to stop or prevent most muscle cramps.
Muscle Spasms
Muscle spasms are involuntary muscle contractions that come on suddenly and are usually quite painful. Dehydration, doing strenuous exercise in a hot environment, prolonged muscle use, and certain diseases of the nervous system may cause muscle spasms. Symptoms and signs of a muscle spasm include an acute onset of pain and a possible bulge seen or felt beneath the skin where the muscle is located. Gently stretching the muscle usually resolves a muscle spasm.
What Do Nerve Conduction Studies and Electromyography Diagnose?
Nerve conduction studies and needle electromyography (EMG) are tests performed to assess the health of nerves and muscles. A neurophysiologist stimulates specific nerves and muscles and studies the resulting activity to evaluate if the nerves and muscles are functioning normally.
Nerve Conduction Velocity Test
A nerve conduction velocity test is an electrical test that detects nerve injury in conditions such as:- peripheral neuropathy,
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Peripheral Neuropathy
Peripheral neuropathy is a problem with the functioning of the nerves outside of the spinal cord. Symptoms may include numbness, weakness, burning pain (especially at night), and loss of reflexes. Possible causes may include carpel tunnel syndrome, shingles, vitamin or nutritional deficiencies, and illnesses like diabetes, syphilis, AIDS, and kidney failure. Peripheral neuropathy is diagnosed with exams and tests. Treatment for the condition depends on the cause. Usually, the prognosis for peripheral neuropathy is good if the cause can be successfully treated or prevented.
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A pinched nerve causes pain, numbness, or tingling in the affected area due to pressure on a nerve. Carpal tunnel and sciatica are two examples of conditions caused by a pinched nerve. A pinched nerve is diagnosed by taking a patient history and performing a physical examination. Electromyography may be performed. Treatment for a pinched nerve depends on the underlying cause.
Sciatica Pain
Sciatica pain, caused by irritation of the sciatic nerve, typically radiates from the low back to behind the thigh to below the knee. Disc herniation is usually the cause of sciatica. Medication to alleviate pain, physical therapy, and bed rest are treatments for sciatica.
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