The 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. The nerves control the muscles by sending electrical signals (impulses) and these impulses make the muscles react in specific ways. In the presence of muscular and nervous disorders, the muscles react abnormally.
The analysis of the electrical activity of the muscles and the nerves is useful for diagnosing muscle diseases (muscular dystrophy) or nerve damage (amyotrophic lateral sclerosis, peripheral neuropathies). EMG and nerve conduction studies are often done together.
EMG is indicated when a disease of the muscle, of the nerve or of the junction between nerve and muscle (neuromuscular junction) is suspected. EMG is also indicated in cases of paralysis or weakness (carpal tunnel syndrome, etc.).
Nerve conduction studies are also indicated when a disease of the peripheral nervous system (multiple sclerosis, Guillain Barré syndrome, etc.) is suspected.