Understanding Electrodiagnostic Testing: EMG and Nerve Conduction Studies Explained

Did you know that your body functions as an electrical generator? Nerves and muscles generate electrical impulses that transmit messages between the brain and the rest of your body.

• Sensory nerves carry information from your environment to the brain.
• Motor nerves send signals from the brain to activate muscle movements.

Injuries or conditions affecting nerves and muscles can disrupt these electrical signals, leading to symptoms such as pain, weakness, or numbness in the back, neck, or limbs. Measuring the speed and strength of electrical activity in the muscles and nerves can help doctors accurately diagnose these issues through a procedure known as electrodiagnostic testing. Two commonly used electrodiagnostic tests include:

• Electromyography (EMG)
• Nerve Conduction Studies (NCS)

These tests are typically performed by neurologists (nerve specialists) or physiatrists (experts in physical medicine and rehabilitation). Most procedures are completed in under an hour.

Electromyography (EMG)

EMG assesses the electrical activity in muscles to evaluate the health of nerves that connect the spinal cord to the muscles. Normally, muscles show no electrical activity when at rest. During the test, small needles are inserted into specific muscles to detect electrical activity. You may experience some discomfort or pain during needle insertion. The doctor will ask you to relax and then slightly tense the muscle while monitoring the electrical signals on a screen and listening to the associated sounds. If you are on blood thinners, have a medical condition, or are at risk of infection, inform the doctor beforehand. Avoid using lotions, creams, or wearing jewelry in the area being tested on the day of the procedure. After the needles are removed, you might experience mild soreness or bruising, which typically resolves within a few days. Long-term side effects are rare. In most cases, test results are available shortly after the procedure.  

Close up of an EMG being performed with a nerve conduction study.

 

Nerve Conduction Studies (NCS)

Nerve conduction studies (NCS) are often performed alongside electromyography (EMG) to assess whether a nerve is functioning properly. During the procedure, the doctor attaches electrodes to the skin at different points along the nerve pathway. The nerve is then stimulated with a mild electric current, allowing the electrodes to detect the speed and strength of the signal as it travels. In healthy nerves, electrical signals can travel up to 120 miles per hour. However, if the nerve is damaged, the signal may be slower or weaker. By stimulating the nerve at multiple locations, the doctor can identify the precise area where the nerve is affected. NCS can also be useful during treatment to track nerve recovery following an injury. While the stimulation may feel surprising at first, it is generally not painful, resembling a static shock similar to touching a doorknob after walking across a carpeted surface.

Conditions That May Require Electrodiagnostic Testing

Orthopedic doctors may recommend electrodiagnostic testing for various conditions involving nerve compression, particularly in the arms, elbows, or wrists. These conditions, known as compressive neuropathies, include:

• Carpal tunnel syndrome: Pressure on the median nerve as it passes through the wrist.
• Thoracic outlet syndrome: Compression of the brachial plexus, a group of nerves located beneath the collarbone.
• Ulnar nerve entrapment: Compression of the ulnar nerve at the elbow or, less commonly, at the wrist.
• Cervical radiculopathy or lumbar radiculopathy: Pressure on nerve roots exiting the spinal cord in the neck or lower back.

Surgeons often use electrodiagnostic testing to evaluate these conditions before considering surgical options.

Applications Beyond Compressive Neuropathies

Electrodiagnostic tests are also valuable in assessing nerve damage from injuries and monitoring the effects of conditions such as diabetes on the nervous system. Additionally, they can help determine whether a damaged nerve is healing.

Accuracy of Electrodiagnostic Testing

The reliability of electrodiagnostic tests largely depends on the skill of the healthcare professional administering the test and the accuracy of the equipment. These tests can effectively identify nerve or nerve root injuries, as well as neuromuscular diseases. However, in certain cases, it may take several weeks for test results to reveal changes. It is important to note that electrodiagnostic tests do not measure the presence or intensity of pain. A person may experience pain or symptoms even if test results indicate normal nerve function. In such instances, an orthopedist may recommend other treatment options.

Emerging Techniques: Ultrasound in Electrodiagnosis

Ultrasound is gaining attention as a complementary or alternative approach to EMG and NCS. This non-invasive technique uses sound waves to create images of nerves and surrounding tissues, allowing physicians to detect signs of nerve compression. In some cases, doctors may recommend an ultrasound alongside EMG/NCS or as a substitute for traditional electrodiagnostic studies.