A diagnostic technique that involves recording and evaluating electrical activity generated by muscles. Electromyography (EMG) can be used to diagnose the underlying cause of tingling, numbness, muscle weakness, muscle pain or cramping, and certain types of limb pain. It is used to diagnose or rule out a wide variety of disorders:

• muscular dystrophy (progressive, symmetrical wasting of the muscles);

• polymyositis (inflammation of multiple muscles);

• myasthenia gravis (chronic weakness of the muscles, especially in the face and throat, due to a defective nerve conduction);

carpal tunnel syndrome (pain in the wrist and hand due to compression of the median nerve);

peripheral neuropathies (general disorders of the nerves outside the brain and spinal cord);

• polio (an infection causing muscle paralysis);

• amytrophic lateral sclerosis (ALS, or “Lou Gehrig’s Disease,” a degenerative disease of the motor neurons causing rapid paralysis); and

• disorders affecting the nerve root, such as a herniated disc.

A fine, sterile needle electrode is inserted into the muscle to be evaluated. A ground electrode is positioned under the patient’s arm or leg. The patient first relaxes and then contracts the muscle as instructed. Electrical activity from the muscle is measured and displayed in the form of waves on a monitor called an oscilloscope. Typically, EMG is performed in conjunction with nerve conduction studies.

Want to learn more about tests for neuropathy? Read “Neuropathy: Diagnosis & Tests.”

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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