Electrodiagnostics

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Electrodiagnostic studies may be performed to help diagnose your spine problem. These studies help determine if a specific symptom, such as pain or weakness, results from a disorder of the muscles or nerves.

Three electrodiagnostic studies:

• Electromyography (EMG)
• Nerve conduction velocity (NCV)
• Somatosensory evoked potential (SSEP)
   

Sometimes, an EMG is performed with NCV and SSEP.

EMG

Electromyography measures muscular response to electric stimulation in the nervous system.  Needle electrodes are inserted through the skin into muscles or muscle groups.  The electrodes record electrical signals from the muscles.  The results measure a muscle’s ability to respond when nerves are stimulated.  EMG can help pinpoint nerve damage.
 

During an EMG, you may be asked to contract muscles by bending an arm or leg.  Sometimes, the test is uncomfortable or painful. It is not unusual to feel muscle soreness for a day or two after EMG. Rare, but potential complications include bleeding or infection at the site of needle insertion.

NCV

A nerve conduction velocity study measures the speed (velocity) at which a nerve carries an electrical impulse.  Electrodes, similar to EKG patches, are placed on the skin along the pathway of the nerve to be tested.  A low electrical impulse stimulates the nerve and the electrode measures the speed at which the electrical current is transmitted.  A damaged nerve will not transmit the electric impulse as quickly as a healthy nerve.  

The test must be done at normal body temperature. Patients undergoing NCV may feel mild electrical shocks or discomfort. Following the test, patients rarely experience any pain or discomfort.

An NCV test is not appropriate for all patients. Some patients, such as those with implantable devices (e.g., pacemaker, deep brain stimulator), may be able to undergo an NCV test with special precautions.

SSEP

Somatosensory evoked potential reveals whether spinal nerves can send and receive sensory messages.  SSEP also measures how quickly these messages are transmitted between the nerve and brain.  Sensory messages are those that transmit pain, a light touch, and temperature.

Conclusion

Electrodiagnostic tests help physicians evaluate spinal conditions by identifying the location of muscle weakness and nerve damage.  Certain electrodiagnostic tests are used during spine surgery to monitor nerve function and avoid injury.