Electromyography (EMG) measures electrical activity inside your muscles. Your muscles produce electrical signals when they work (contract). To find out if your muscles are working correctly, you might have an EMG.
Doctors use electromyography to help diagnose the causes of:
- Arm or leg pain
- Numbness or tingling
- Weakness or cramping
If an imaging test such as an MRI does not adequately explain all your symptoms, you might have an EMG. You may also have an EMG if the doctor thinks more than one health problem could be causing your symptoms.
An EMG can help evaluate nerve problems such as polyneuropathies (damage to several nerves). These can be caused by conditions such as diabetes. If you have spine problems, your doctor might do an EMG to evaluate a pinched nerve in your neck or lower back (radiculopathy).
It takes 25 to 30 minutes to test one arm or leg. Your doctor does a brief history and physical exam to identify the muscles that need to be tested. Next, the doctor places very small needles in these muscles. The needles are very thin (like acupuncture needles) and the doctor inserts them about one-eighth to one-quarter inch under your skin. Putting in the needles takes only a minute or two. The doctor can study three to seven muscles at a time.
Your doctor will ask you to relax and then gently contract (squeeze) the muscle. The needles are connected to a nearby machine. When the needle picks up electrical activity in your muscles, it sends the signals to a nearby machine. The machine produces graphs, sounds, or numbers that tell the doctor how well your muscles are working.
Your doctor will evaluate the information recorded by the needle. If the nerves or muscles are damaged, your doctor can see this easily. He or she can also tell which nerves or muscles are damaged.
Your doctor might send a mild electric current to the muscle through a needle or small patch (electrode). This feels like a small static electricity shock, and some people describe the feeling as a “strong tap.” Another needle or electrode picks up the signal and sends it to the machine.