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Electromyography (EMG) Testing

Before your electromyogram (EMG), you may have questions about how to prepare and what will happen during the test. The information below will help answer your questions and provide you with instructions to follow before you arrive for your test.

Should you need additional information, please contact Mischer Neuroscience Institute at (713) 704-2144.

What is an 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 are EMGs done?

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

How do I prepare for an EMG?

The neurologist conducting the EMG will need to know if you have certain medical conditions. Tell the neurologist and other

EMG lab personnel if you:

  • Have a pacemaker or any other electrical medical device
  • Take blood-thinning medications
  • Have hemophilia, a blood-clotting disorder that causes prolonged bleeding

Take a shower or bath shortly before your exam to remove oils from your skin. Don’t apply lotions or creams before the exam.

What should I expect?

You will likely be asked to change into a hospital gown for the procedure and lie down on an examination table. The neurologist or a technologist will place surface electrodes at various locations on your skin depending on where you are experiencing symptoms. The neurologist may insert needle electrodes at different sites depending on your symptoms.

The electrodes will at times transmit a tiny electrical current that you may feel as a twinge or spasm. The needle electrode may cause discomfort or pain that usually ends shortly after the needle is removed.

If you’re concerned about discomfort or pain, you may want to talk to the neurologist about taking a short break during the exam.

During the needle EMG, the neurologist will assess whether there is any spontaneous electrical activity when the muscle is at rest — activity that isn’t present in healthy muscle tissue — and the degree of activity when you slightly contract the muscle.

The doctor will give you instructions on resting and contracting a muscle at appropriate times. Depending on what muscles and nerves the neurologist is examining, he or she may ask you to change positions during the exam.

After your EMG, you may experience some temporary, minor bruising where the needle electrode was inserted into your muscle. This bruising should fade within several days. If it persists, contact your primary care doctor.

Should you have any questions about your test, please contact Mischer Neuroscience Institute at (713) 704-2144.