If your doctor has referred you for an EMG test, you might feel unsure about what it involves or why your doctor recommended it. This blog will provide an overview of this nerve conduction study/ EMG diagnostic test to help you feel prepared and informed.

 

What is a nerve conduction study/EMG Test?

An NCS/EMG test combines two diagnostic procedures: nerve conduction studies (NCS) and electromyography (EMG).
 
Specialist doctors often perform these tests together to evaluate the health of your nerves and muscles.
  • Nerve Conduction Studies (NCS): This test measures how well electrical signals travel along the nerve. Small electrodes are placed on your skin to stimulate the nerves with a mild electrical impulse, and the response is recorded.
  • Electromyography (EMG) measures the electrical activity of your muscles. A thin electrode, roughly the thickness of an acupuncture needle, is inserted into the muscle to record its activity at rest and during movement.
Together, these tests provide a detailed picture of how well your nerves and muscles work.
 
Male having EMG study of lower leg

Why is an NCS/EMG Test Done?

We use the NCS/EMG test to diagnose or evaluate conditions affecting the peripheral nervous system (PNS) and muscles. The PNS is the part of the nervous system that lies outside the brain and spinal cord (the central nervous system, or CNS). It consists of nerves and nerve cell bodies (ganglia) that connect the CNS to the rest of the body. The PNS enables communication between the CNS, limbs, organs, and tissues. 
 
Common reasons for the test include:
  • Diagnosing Peripheral Nerve Disorders:
  • Assessing Neuromuscular Junction Disorders:
    • Myasthenia gravis
  • Investigating Unexplained Symptoms:
    • Numbness
    • Tingling
    • Muscle weakness
    • Chronic pain
It is important to note that NCS/EMG cannot diagnose neurological symptoms such as numbness, tingling, muscle weakness, or pain resulting from conditions affecting the central nervous system (CNS), such as stroke, spinal cord injury, or multiple sclerosis (MS). 
 

What Should Patients Expect During an EMG Test?

Understanding what happens during the test can ease your nerves and help you prepare.

Before the Test:

  • Wear loose, comfortable clothing that allows easy access to the areas being tested. Shorts and short-sleeve T-shirts are ideal for the procedure. The doctor may need to access your arms, legs, neck, and/or back muscles.
  • Avoid using lotions or oils on your skin, as they can interfere with the electrodes.
  • Inform your doctor about any medications or medical conditions, as some may affect the results.

During Nerve Conduction Studies (NCS):

  • Small electrodes will be placed on your skin over the nerve being tested.
  • Your doctor delivers a small electrical pulse through the electrode to the nerve. This pulse stimulates the nerve, and your doctor notes the response. You will feel a quick, mild electric shock or tingling sensation. You may also notice your muscles twitch as a result of electrical stimulation. It might be uncomfortable, but most people tolerate the test well.  
  • The process is repeated multiple times and at different locations to gather all the necessary data to assess whether the nerves are functioning normally.

During Electromyography (EMG):

  • A thin needle electrode, about the thickness of an acupuncture needle, is inserted into your muscle to measure its electrical activity.
  • You may feel some discomfort during the insertion, similar to a pinprick.
  • Your doctor will ask you to relax or contract the muscle at certain times during the test.

After the Test:

  • You can resume normal activities immediately after the test.
  • Some patients experience mild soreness in the tested muscles, which usually resolves within a day.

How Long Does the EMG Test Take?

The duration of the test depends on the areas evaluated, but it generally takes between 30 and 90 minutes, depending on the complexity of the particular exam nation. Typically, your doctor will review the results and discuss the findings with you at a follow-up appointment.
 

Is the EMG Test Safe?

Yes, NCS and EMG tests are very safe. The electrical impulses used in NCS are mild and controlled, and the needle electrodes used in EMG are sterilised to prevent infection. Serious complications are infrequent.
 
NCS can generally be performed on individuals with pacemakers or other implanted medical devices. However, informing your doctor about these devices is essential so appropriate precautions can be taken. Similarly, EMG can be performed if you are taking anticoagulants; however, it is crucial to inform the doctor conducting the procedure so necessary precautions can be taken to minimise the risk of bleeding.
 

Other frequently asked questions about an EMG test

How long does a nerve conduction study take?

Generally, a combined NCS/EMG test takes about 30-45 minutes to complete. However, it can take up to 90 minutes in more complex cases. 

What medications affect a nerve conduction study?

Certain medications may influence the results of a nerve conduction study, including muscle relaxants, anticholinergics, sedatives, nerve-blocking agents, chemotherapy drugs, and anticonvulsants. Additionally, anticoagulation medications may increase the risk of bruising or bleeding during an EMG. You must inform your doctor about all medicines, including over-the-counter drugs and supplements.

Is a nerve conduction study painful?

While not typically painful, some people describe the sensation as mildly uncomfortable. You may feel:
  • A tingling or zapping sensation from the small electrical impulses.
  • Discomfort varies based on individual pain thresholds and nerve sensitivity.

Does MS show up in a nerve conduction study?

Nerve conduction studies can detect peripheral nerve damage, but multiple sclerosis (MS) primarily affects the central nervous system (CNS). Therefore:
  • NCS is not diagnostic for MS.
  • Tests like MRI or spinal fluid analysis are more commonly used for MS diagnosis.

Do some hairy people need to shave before EMG electrodes?

Hair can interfere with electrode contact, so shaving may be suggested in areas with thick or dense hair. However:
  • Doctors can often prepare the skin by cleaning or lightly abrading the area without requiring shaving.

How accurate is a nerve conduction test for carpal tunnel?

Nerve conduction studies (NCS) are generally considered accurate for diagnosing carpal tunnel syndrome (CTS). However, the accuracy of NCS can vary depending on the number of nerves tested.

Can I take a narcotic before an EMG test?

You can generally take a narcotic or other prescribed medications before an EMG, but:
  • Inform your doctor about the dose and timing.
  • Pain medications might slightly alter your perception of discomfort during the test but do not typically affect the results.

How do I make EMG less painful?

Here are tips to reduce discomfort during EMG:
  • Relax your muscles during the procedure.
  • Use over-the-counter pain relief (e.g., ibuprofen) before the test if approved by your doctor.
  • Stay warm before the test; cold muscles can be more sensitive.
  • Communicate with your doctor if discomfort becomes too intense.

Final word about Nerve conduction study/ EMG Test

NCS/EMG test is a valuable tool for diagnosing and understanding peripheral nerve and muscle conditions. Measuring electrical signals in your peripheral nerves and muscles can help diagnose conditions that cause symptoms like pain, weakness, or numbness.
 
Dr. Marco Masci is a Board-Certified Physician in Physical Medicine and Rehabilitation (PM&R). He is an electrodiagnostic studies (NCS/EMG) expert. He assesses general musculoskeletal patients with Kaiser Permanente in the Los Angeles area.