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Electromyogram (EMG)


Electromyography is a test that assesses the state of the muscles and the nerves controlling the muscles.

How is the test performed?

For an EMG, a needle electrode is inserted through the skin into the muscle. The electrical activity detected by this electrode is displayed on a display screen, and may be heard through a speaker. After placement of the electrodes, you may be asked to contract the muscle (for example, by bending your arm). The presence, size, and shape of the wave-form (the action potential) produced on the screen provide information about the ability of the muscle to respond when the nerves are stimulated. A Nerve conduction study (NCS) test is usually performed in conjunction with an EMG.

How to prepare for the test:

No special preparation is usually necessary. Avoid using any creams or lotions on the day of the test. You may have to remove some jewellary or metals from the site of examination.

How will it feel?

You may feel some pain or discomfort when the electrodes are inserted, but most people are able to complete the test without much difficulty. Afterwards, occasionally the muscle may feel tender or bruised for a few  hours or days.

Why is the test performed?

EMG is most often used when people have symptoms of weakness and examination shows impaired muscle strength. It can help to differentiate primary muscle conditions from muscle weakness caused by neurologic disorders.

Normal results or values:

Muscle tissue is normally electrically silent at rest. Once the insertion activity (caused by the trauma of needle insertion) quiets down, there should be no action potential on the oscilloscope. When the muscle is voluntarily contracted, action potentials begin to appear. As contraction is increased, more and more muscle fibers produce action potentials until a disorderly group of action potentials of varying rates and amplitudes (complete recruitment and interference pattern) appears with full contraction.

Abnormal results:

Disorders or conditions that cause abnormal results include the following:

  • Denervation such as is seen in cervical or lumbosacral radiculopaties.This examination helps us to identify the severity and exact localization of the nerve root involvement
  • Polymyositis
  • Carpal Tunnel Syndrome
  • Thoracic neurogenic outlet syndrome
  • Lumbosacral Plexopathy
  • Amyotrophic Lateral Sclerosis (ALS)
  • Myopathy (muscle degeneration)
  • Myasthenia gravis
  • Muscular dystrophies
  • Alcoholic neuropathy
  • Axillary nerve dysfunction
  • Becker’s muscular dystrophy
  • Brachial plexopathy
  • Cervical spondylosis
  • Common peroneal nerve dysfunction
  • Dermatomyositis
  • Distal median nerve dysfunction
  • Duchenne muscular dystrophy
  • Facioscapulohumeral muscular dystrophy
  • Familial periodic paralysis
  • Femoral nerve dysfunction
  • Friedreich’s ataxia
  • Guillain-Barre Syndrome
  • Lambert-Eaton Syndrome
  • Monoeuritis multiplex
  • Monoeuropathy
  • Peripheral neuropathy
  • Radial nerve dysfunction
  • Sensorimotor polyneuropathy
  • Shy-Drager syndrome
  • Thyrotoxic periodic paralysis
  • Tibial nerve dysfunction
  • Ulner nerve dysfunction

What are the risks?

  • Bleeding (minimal)
  • Infection at the electrode sites (minimal risk)
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Diagnostics & Conditions - Warwickshire Neurophysiology Clinic
Electromyogram (EMG) - Warwickshire Neurophysiology Clinic
Nerve Conduction Studies (NCS) - Warwickshire Neurophysiology Clinic
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