Electromyography

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Electromyography

EMG; Myogram

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.

Disorders or conditions that cause abnormal results include the following:

• Polymyositis
• Denervation (reduced nervous stimulation)
• Carpal tunnel syndrome
• Amyotrophic lateral sclerosis (ALS)
• Myopathy (muscle degeneration, may be caused by a number of disorders, including muscular dystrophy)
• Myasthenia gravis
• 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 (Landouzy-Dejerine)
• Familial periodic paralysis
• Femoral nerve dysfunction
• Friedreich's ataxia
• Guillain-Barre
• Lambert-Eaton Syndrome
• Mononeuritis multiplex
• Mononeuropathy
• Peripheral neuropathy
• Radial nerve dysfunction
• Sciatic nerve dysfunction
• Sensorimotor polyneuropathy
• Shy-Drager syndrome
• Thyrotoxic periodic paralysis
• Tibial nerve dysfunction
• Ulnar nerve dysfunction

Review Date: 09/26/2006
Reviewed By: Kenneth Gross, M.D., Neurology, North Miami, FL. Review provided by VeriMed Healthcare Network.