Electromyography (EMG) test
Nerves and muscles work together within the neuromuscular system. When you want to move, your brain relays electrical signals to the muscles via the spinal cord and nerves, and those signals tell the muscles what to do.
If the nerves or muscles become damaged, communication can break down. The result is muscle weakness, numbness, tingling, and in severe cases, difficulty moving the areas of the body where the nerves and muscles are damaged. If you’re experiencing these symptoms, your doctor may recommend nerve conduction studies including an electromyography (EMG) test.
What is an electromyography (EMG) test?
An electromyography (EMG) test helps diagnose muscular and neurological 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 an electromyography (EMG) test is a nerve conduction study, which measures the amount and speed of electrical activity through the nerve to determine nerve damage. 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. Experts say it's a similar feeling to getting a shock when you’re walking on carpeting.
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.
Why would my doctor want me to have an electromyography (EMG) test?
In some neuromuscular diseases, the nerves are damaged, and in others the muscles are damaged. Either way, the damage can lead to fatigue, weakness, muscle pain and spasms. Symptoms usually occur in the legs and arms, making electromyography (EMG) testing most common on the legs and arms.
Your doctor may order an electromyography (EMG) test if you experience any of the following symptoms:
- Numbness
- Decreased sensation
- Tingling or frequent feeling of "pins and needles" in your legs, feet, arms or hands
- Radiating pain or burning sensation
- Muscle spasms or weakness
- Difficulty performing daily tasks such as walking, buttoning clothes or handling objects
What can an electromyography (EMG) test find out?
An electromyography (EMG) test looks at 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, sciatica and peripheral neuropathy. The test is also used to look for damage to the nerve roots that exit the spinal cord and become pinched by discs or bony material of the spine (radiculopathy).
An electromyography (EMG) test is also used to diagnose rarer conditions such as muscle disease (myopathy), amyotrophic lateral sclerosis (ALS), Charcot-Marie-Tooth disease, muscular dystrophy, myasthenia gravis and multiple sclerosis.
What to expect during an electromyography (EMG) test
An electromyography (EMG) test is performed by a neurologist (a doctor who specializes in brain and nerve disorders). A technologist may also perform some portions of the test.
Generally, an EMG procedure follows this process:
- You will be asked to remove any jewelry, eyeglasses, hearing aids or other items containing metal, which can interfere with the procedure. If you're asked to remove clothing, you will be given a gown to wear.
- The neurologist will locate the muscles to be studied and clean that area of the skin.
- Next, they’ll insert a fine, sterile needle into the affected muscle.
- You may experience slight pain when the needle goes in. The sensation is similar to getting a shot or having your blood drawn. There’s no need for a topical anesthetic, and you’ll be awake for the entire test.
- You’ll be asked to relax and then perform slight or full-strength muscle contractions.
- The electrical activity from your working muscle will be measured and displayed on an instrument called an oscilloscope.
- An audio amplifier may also be used so that both the appearance and sound of the electrical potentials can be evaluated. If the recorder is attached to an audio amplifier, you may hear a sound like hail on a tin roof when you contract your muscle.
Steps 2-7 will be repeated for each muscle being studied. After the test is over, you may experience some temporary, minor tingling where the needle electrode was inserted into your muscle. You’ll be fine to drive home and resume all your usual activities right away. You may develop slight bruising where the needles were inserted, but it should fade within 1- 2 days. If bruising or pain persists, contact your doctor.