Electromyography (EMG) test
Every movement you make requires communication between the brain and the muscles. The nervous system provides the link between thoughts and actions by relaying messages from the brain to other parts of the body through electrical activity.
Nerves and muscles work together within the neuromuscular system to make your body move how you want and even control functions such as breathing.
When nerves are damaged, they can’t carry messages from the brain and nerves like they should. When muscles are damaged, they either can't receive messages from the brain and nerves, or they can't respond like they should.
Either way, the damage can cause tiredness, weakness, tingling, muscle pain and spasms. The symptoms often affect the arms and legs more than other parts of the body. Your doctor may order nerve conduction studies including an electromyography (EMG) test to determine the exact cause of your symptoms.
Reasons to get an electromyography (EMG) test
Your doctor may recommend electromyography (EMG) testing if you experience any of the following symptoms:
- Decreased sensation
- Difficulty performing daily tasks such as walking, buttoning clothes or handling objects
- Muscle spasms or weakness
- Numbness
- Radiating pain or burning sensation
- Tingling or frequent "pins and needles" sensations in the arms, legs, hands or feet
Symptoms usually occur in the legs and arms, making electromyography (EMG) testing most common on these areas.
What is an EMG test?
Electromyography (EMG) is a diagnostic test that evaluates the health and function of skeletal muscles and the nerves that control them. The test measures muscle response or electrical activity in response to a nerve's stimulation of the muscle.
An electromyography (EMG) test helps diagnose neuromuscular conditions by recording electrical activity in affected areas of your body. A tiny needle electrode translates your nerve signals into graphs, sounds and numbers that are then interpreted by a specialist.
Another part of electromyography (EMG) testing is a nerve conduction study, which measures the amount and speed of electrical activity through the nerve to determine nerve damage and destruction. During nerve conduction studies, two electrodes are placed on the skin over your nerve. One electrode stimulates your nerve with a very mild electrical impulse. The other electrode records it. The resulting electrical activity is recorded by another electrode. This is repeated for each nerve being tested.
At the end of the nerve conduction study, the speed of electrical activity is calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.
What does an electromyography (EMG) test diagnose?
An electromyography (EMG) test assesses the health of muscle tissue and the peripheral nervous system, which includes all the nerves outside the brain and the spinal cord.
It evaluates common conditions such as carpal tunnel syndrome, pinched nerves and sciatica. The electromyography (EMG) test also looks for damage to the nerve roots that exit the spinal cord. These roots can become inflamed by discs or bony material of the spine and cause radiculopathy.
Electromyography (EMG) testing can also be used to diagnose more rare conditions such as amyotrophic lateral sclerosis (ALS), myasthenia gravis (MG), muscle disease (myopathy), muscular dystrophy, Charcot-Marie-Tooth disease and multiple sclerosis (MS).
What to expect during an electromyography (EMG) test
The test usually consists of two parts: needle electromyography (EMG) testing and nerve conduction studies.
During the electromyography (EMG) test, the doctor inserts a small, thin needle into several muscles. Electrical signals travel from the needle to the EMG machine, allowing the doctor to hear and see how your muscles and nerves are working.
During the nerve conduction studies, the doctor applies small electrical shocks to your nerves to study how they work. The shocks cause a mild tingling feeling like when you get a shock while walking on carpeting. Let the doctor know at any time if the pain is too much. You can take a break at any time until you feel more comfortable.
The doctor then studies the results of both parts of the test to determine the cause of your symptoms.
You may experience some temporary, minor bruising where the needle electrode was inserted into your muscle. If the bruising doesn’t go away after several days, contact your doctor.