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 the 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.
Amyotrophic lateral sclerosis facts*
*Amyotrophic lateral sclerosis facts medical author: William C. Shiel Jr., MD, FACP, FACR
- Amyotrophic lateral sclerosis is a rapidly progressive, invariably fatal neurological disease that attacks the nerve cells responsible for controlling voluntary muscles.
- Amyotrophic lateral sclerosis, or ALS, is sometimes called Lou Gehrig's disease.
- As many as 20,000 to 30,000 people in the United States have ALS, and an estimated 5,000 people in the United States are diagnosed with the disease each year.
- Only about 5 to 10 percent of all ALS cases are inherited in the family's genes.
- Early symptoms of ALS are subtle and may include twitching, cramping, or stiffness of muscles; muscle weakness affecting an arm or a leg; slurred and nasal speech; or difficulty chewing or swallowing.
- No one test can provide a definitive diagnosis of ALS, although the presence of upper and lower motor neuron signs in a single limb is strongly suggestive.
- The cause of ALS is not known, and scientists do not yet know why ALS strikes some people and not others. Scientists have discovered that mutations in the gene that produces the SOD1 enzyme were associated with some cases of familial ALS.
- No cure has yet been found for ALS. The first drug treatment for the disease -- riluzole (Rilutek) is believed to reduce damage to motor neurons by decreasing the release of glutamate. Clinical trials with ALS patients showed that riluzole prolongs survival by several months and extends the time before a patient needs ventilation support. Other treatments for ALS are designed to relieve symptoms and improve the quality of life for patients.
What is amyotrophic lateral sclerosis?
Amyotrophic lateral sclerosis (ALS), sometimes called Lou Gehrig's disease, is a rapidly progressive, invariably fatal neurological disease that attacks the nerve cells (neurons) responsible for controlling voluntary muscles. The disease belongs to a group of disorders known as motor neuron diseases, which are characterized by the gradual degeneration and death of motor neurons.
Motor neurons are nerve cells located in the brain, brainstem, and spinal cord that serve as controlling units and vital communication links between the nervous system and the voluntary muscles of the body. Messages from motor neurons in the brain (called
upper motor neurons) are transmitted to motor neurons in the spinal cord (called
lower motor neurons) and from them to particular muscles. In ALS, both the upper motor neurons and the lower motor neurons degenerate or die, ceasing to send messages to muscles. Unable to function, the muscles gradually weaken, waste away (atrophy), and twitch (fasciculations) . Eventually, the ability of the brain to start and control voluntary movement is lost.
ALS causes weakness with a wide range of disabilities (see section titled "What are the symptoms?"). Eventually, all muscles under voluntary control are affected, and patients lose their strength and the ability to move their arms, legs, and body. When muscles in the diaphragm and chest wall fail, patients lose the ability to breathe without ventilatory support. Most people with ALS die from respiratory failure, usually within 3 to 5 years from the onset of symptoms. However, about 10 percent of ALS patients survive for 10 or more years.
Although the disease usually does not impair a person's mind or intelligence, several recent studies suggest that some ALS patients may have alterations in cognitive functions such as depression and problems with decision-making and memory.
ALS does not affect a person's ability to see, smell, taste, hear, or recognize touch. Patients usually maintain control of eye muscles and bladder and bowel functions, although in the late stages of the disease most patients will need help getting to and from the bathroom.