EMG NCV Test: Overview, Purpose & Preparation

Overview
Electromyography and nerve conduction velocity tests are electrodiagnostic tools used to evaluate the electrical impulses of nerves and muscles. Nerves transmit electrical signals to your muscles, prompting them to respond in specific ways, and the resulting muscle activity can be measured by these tests.

• An EMG test is used to study the electrical signals produced by your muscles while they are at rest and during activity.
• A NCV test is performed to assess the speed and efficacy of electrical signals that travel along the body’s nerves. This is also known as conduction velocity.

Both EMG and NCV testing can help determine if you are suffering from disorders of the nerves, muscles, or both. These assessments can be performed separately; however, they are frequently carried out together.

Your doctor may order these tests if you are exhibiting the symptoms of neurological or muscular disorders, such as unexplained numbness or weakness in your limbs.
EMG and NCV tests are low-risk (safe) examinations; however, they can result in bruising and discomfort at the needle’s insertion point.

Keep reading to learn more about their purpose, how to prepare for it, and what to expect during the test.

Purpose of EMG-NCV tests

Neurons, also known as motor nerve cells, send electrical impulses from your brain’s central nervous system to your muscles. These electrical impulses from nerves trigger contractions in the muscles.

These motor nerves regulate your skeletal muscle activities, including walking, breathing, and speaking.
If muscle fibres are diseased or impaired, they may fail to respond appropriately to nerve impulses. Also, if the motor nerves are diseased or damaged, they may send abnormal electrical signals to your muscles.

If you exhibit signs of a nerve or muscle ailment, your doctor may request an EMG and NCV test.

Such symptoms may include:

• Muscle weakness or stiffness
• Muscle spasms, twitches, and cramps
• Muscle wasting (muscle atrophy)
• Reduced fine motor control
• Difficulty chewing, swallowing, or speaking
• Persistent pain in arms, legs, hands, or feet
• Tingling, numbness, or paralysis in the limbs

These tests may also be helpful in detecting the extent and exact location of the nerve or muscle damage.

What do the tests show?

Both tests can assist doctors in determining what is wrong with your nerves and muscles. EMG and NCV can help with the following diagnoses:

• Neuromuscular disorders (for instance, muscular dystrophy)
• Spinal nerve disorders, for example, a herniated disc
• Nerve issues in other parts of the body, including carpal tunnel syndrome
• Problems with peripheral nerves in the arms or legs
• Nerve impingement
• Guillain-Barré syndrome (a disorder that causes your immune system to attack the nerves in your arms and legs)
• Myasthenia gravis (an uncommon illness that causes muscle weakness and fatigue)
• Charcot-Marie-Tooth disease (a hereditary nerve condition that mostly affects the legs and arms)

Preparation for the EMG and NCV tests

These tests can be carried out as an outpatient procedure or in a hospital setting by a neurologist or skilled technician.

Prior to the test, your doctor will take you through the procedure of how the test is conducted and what preparations you may need to do for it. Any doubts you might have should be cleared at this point.

You must inform your neurologist if you:

• Are taking any medications, particularly blood thinners, or even if you are taking over-the-counter medications.
• Have bleeding disorders.
• Have a pacemaker or a cardiac defibrillator. If you’ve got any of these devices, you may have to take additional measures before the test.

In order to prepare for the EMG NCV tests, you must:

• Take a shower prior to the tests so as to remove any excess oil from your skin.
• Keep away from applying lotions, creams, or oils to the skin for a few days before the test.
• Dress comfortably in loose-fitting clothing. It allows easy access to the testing area or can be readily taken off if it requires changing to a hospital gown.
• Take off any jewellery,  eyeglasses, watches, or other metal items before the procedure.
• Avoid sugary beverages and caffeine for at least 2 to 3 hours before a test.
• Not smoke before taking the test.

What to expect during the test?

For an EMG test:

• You will be asked to sit or lie down on an exam bed or table.
• Your medical provider will clean the area of the skin over the muscle that is tested.
• A needle electrode (a specialised wire through which a mild electric current flows) will be inserted into the muscle by your healthcare provider. You might experience mild discomfort or pain while the electrode is being inserted.
• The EMG machine then records the muscle activity while the muscle is at rest.
• Then, you will be instructed to tighten the muscle gradually in order to record this muscle activity.
• Your healthcare provider may move the electrode to record the muscle activity in different muscles.
• This electrical activity is displayed on a video screen as spiky and wavy lines on the screen and may also be recorded and played back through an audio speaker, which may produce popping sounds when you tighten (contract) your muscle.
  For an NCV test:
• You will be instructed to sit or lie down on an exam bed or table.
• Using paste or tape, your healthcare provider will secure multiple electrodes to a specific nerve or nerves. These electrodes are also referred to as stimulating electrodes and deliver a modest electrical pulse.
• Your medical provider may attach multiple types of stimulating electrodes to your muscle or muscles that are regulated by those nerves in order to capture the nerve’s responses to the electrical stimulation.
• Your healthcare provider will then transmit a small electrical pulse by using stimulating electrodes in order to stimulate the nerve and send out a signal to the muscle. This may result in a mild tingling sensation.
• The time it takes for your muscle to react to the nerve signal will be measured, which is known as the conduction velocity.
  If you are advised to do both tests, the nerve conduction velocity test will be performed first.

What to expect after the procedure?

• The technician or neurologist will remove all the needles and electrodes after finishing the test.
• The area of the skin will be cleaned, and you may be able to return to your daily routine.
• Depending on your condition, your healthcare practitioner might give you additional instructions following the procedure.

Potential risks associated with EMG and NCV tests

The testing has a very little risk of serious consequences or adverse effects; however, some people may experience the following sensations:

• During an EMG test, they may experience mild discomfort or muscle cramping.
• During a nerve conduction test, they may experience a tingling sensation similar to a little electric shock.

Takeaway

Both EMG and NCV tests are important diagnostic tools used to assess the health of nerves and muscles in the body. These tests can help healthcare providers diagnose a range of conditions and determine appropriate treatment plans. While both tests may cause some discomfort, they are generally safe and well-tolerated. It is important to follow any preparation instructions provided by your healthcare provider prior to the tests to ensure accurate results.