An electromyogram (EMG) measures the electrical activity of muscles at rest and during contraction. Nerve conduction studies measure how well and how fast the nerves can send electrical signals. Nerves control the muscles in the body by electrical signals (impulses), and these impulses make the muscles react in specific ways. Nerve and muscle disorders cause the muscles to react in abnormal ways.

Measuring the electrical activity in muscles and nerves can help find diseases that damage muscle tissue (such as muscular systrophy) or nerves (such as amyotrophic lateral aclerosis or peripheral neuropathies). EMG and nerve conduction studies are often done together to give more complete information.

Why It Is Done

An electromyogram (EMG) is done to:

• Find diseases that damage muscle tissue, nerves, or the junctions between nerve and muscle (neuromuscular junctions). These disorders may include a herniated disc, amyotrophic lateral sclerosis (ALS), or myasthenia gravis (MG).
• Find the cause of weakness, paralysis, or muscle twitching. Problems in a muscle, the nerves supplying a muscle, the spinal cord, or the area of the brain that controls a muscle can cause these symptoms. The EMG does not show brain or spinal cord diseases.

Nerve conduction studies are done to:

• Find damage to the peripheral nervous system, which includes all the nerves that lead away from the brain and spinal cord and the smaller nerves that branch out from those nerves. Nerve conduction studies are often used to help find nerve disorders, such as carpal tunnel syndrome or Guillain-Barre syndrome.