Our body is an electric signal generator.  Muscles and nerves create electric signals that travel to and from our brain.  Nerves are divided into motor and sensory nerves.  Motor nerves deliver signals to activate our muscles.  Sensory nerves deliver information to our brain about our surroundings.

There are conditions that can slow or prevent the electrical signals to reach their target.  Measuring the velocity and degree of electric activity in your muscles or nerves can aid on the diagnosis of several conditions such as carpal tunnel syndrome or cervical/lumbar radiculopathy.

Electrodiagnostic studies usually involve two parts: electromyography (EMG) and nerve conduction studies (NCS).

Nerve conduction studies (NCS)

NCS are often done along with the EMG to determine if a nerve is functioning normally. The doctor conducting the test will tape wires (electrodes) to the skin in various places along the nerve pathway. Then the doctor stimulates the nerve with an electric current. As the current travels down the nerve pathway, the electrodes placed along the way capture the signal and time how fast the signal is traveling. If the nerve is damaged, however, the signal will be slower and weaker. By stimulating the nerve at various places, the doctor can determine the specific site of the injury. Nerve conduction studies also may be used during treatment to test the progress being made.

Although you may initially be startled by the suddenness of the stimulation, it is not painful and most people are comfortable during the testing procedure. The shock is similar to one received when you touch a doorknob after walking across carpeting.

Your physician may recommend electrodiagnostic testing for various conditions that can result from pressure on a nerve, particularly in the arm, elbow or wrist. These conditions are called “compressive neuropathies” and include:

  • carpal tunnel syndrome (pressure on the median nerve as it passes between the wrist bones and under the transverse ligament)
  • ulnar nerve entrapment (pressure on the ulnar nerve as it passes behind the elbow)
  • cervical radiculopathy (pressure on the nerve roots as they exit the spinal column at the neck)

Electrodiagnostic testing also can be used to determine the extent of injury to a nerve after an accident and to study the effects of diseases such as diabetes. Your health insurance company or HMO may require electrodiagnostic testing to confirm a diagnosis before authorizing medical or surgical treatment.

Electromyography (EMG)

An EMG records and analyzes the electrical activity in your muscles. It is used to learn more about the functioning of nerves in the arms and legs. When a normal muscle is at rest, it is electrically silent.

During an EMG, small, thin needles are placed in the muscle to record the electrical activity. When the needles are inserted, you may feel some pain and discomfort. The doctor will ask you to relax the muscle and to tense it slightly. The doctor will listen and watch a TV-like screen that broadcasts the electrical signals. You will also be able to hear the signal sounds as you move the muscle. When the needles are removed, you may experience some soreness and bruising, but this will disappear in a few days. There are no long-term side effects.

If you are taking blood-thinning medications, have lung disease or are at risk for infection, tell the physician who is conducting the test. On the day of the test, bring shorts for lower extremity testing and short sleeve shirts for upper extremity testing.  Do not put any lotions or creams on the area to be tested and do not wear any jewelry.

Ref: http://orthoinfo.aaos.org/topic.cfm?topic=a00270

Video explanation of electrodiagnostic test: http://www.youtube.com/watch?v=k0uSpYd_Ics

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