Electromyography (EMG)

Electromyography (EMG) is a diagnostic procedure to assess the health of muscles and the nerve cells that control them (motor neurons).

Motor neurons transmit electrical signals that cause muscles to contract. An EMG translates these signals into graphs, sounds or numerical values that a specialist interprets.

An EMG uses tiny devices called electrodes to transmit or detect electrical signals.

During a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle.

A nerve conduction study, another part of an EMG, uses electrodes taped to the skin (surface electrodes) to measure the speed and strength of signals traveling between two or more points.

EMG results can reveal nerve dysfunction, muscle dysfunction or problems with nerve-to-muscle signal transmission.

Why it's done Risks How you prepare What you can expect Results

Your doctor may order an EMG if you have signs or symptoms that may indicate a nerve or muscle disorder. Such symptoms may include:

  • Tingling
  • Numbness
  • Muscle weakness
  • Muscle pain or cramping
  • Certain types of limb pain

EMG results are often necessary to help diagnose or rule out a number of conditions such as:

  • Muscle disorders, such as muscular dystrophy or polymyositis
  • Diseases affecting the connection between the nerve and the muscle, such as myasthenia gravis
  • Disorders of nerves outside the spinal cord (peripheral nerves), such as carpal tunnel syndrome or peripheral neuropathies
  • Disorders that affect the motor neurons in the brain or spinal cord, such as amyotrophic lateral sclerosis or polio
  • Disorders that affect the nerve root, such as a herniated disk in the spine

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