EMG & Nerve Conduction
Diagnostic tests for muscle and nerve function.
A Nerve Conduction Study and an Electromyography (EMG) are diagnostic tests used to evaluate the health and function of muscles and the nerves that control them.
These tests are often done together because they can provide complementary information. For example, if a patient has weakness in a particular muscle, the combination of NCS and EMG can help determine whether the problem originates in the nerve, the muscle, or somewhere in between.
Nerve Conduction Study
A nerve conduction study (NCS) evaluates the ability of the nerves in the limbs to conduct impulses that underlie the functions of feeling and movement.
For these normal impulses to be recorded, electrodes are applied to the skin’s surface. Then, the nerve being assessed has a small electrical current (shock) applied to it and the speed at which the electrical impulse travels along the nerve is measured.
What does a nerve conduction test diagnose? The NCS can locate nerve damage, the severity of the damage, and can help determine the underlying cause, such as nerve compression (e.g., carpal tunnel syndrome) or neuropathies (e.g., diabetic neuropathy).
Repetitive Stimulation Study
This advanced NCS technique evaluates the integrity of the neuromuscular junction by repeatedly stimulating a target muscle. We then measure the compound action potential, which is the sum of nerve electrical signals from several muscle fibres. A reduction or decrement of these responses is consistent with muscle fatiguability, so this test is used to diagnose neuromuscular junction disorders, such as myasthenia gravis.
How to prepare.
DO
- Wear a sleeveless top (such as a camisole or vest) and/or shorts (depending on the limb being assessed).
- Please let us know if you are on any blood thinners or have a skin infection.
DON’T
- Apply lotion or moisturisers on the day of the appointment.
Electromyography (EMG)
After the Nerve Conduction Study, further testing may be required through an EMG test. An EMG test evaluates the electrical activity in muscles using a fine disposable needle electrode. The needle is inserted into the muscle being tested and measures the electrical activity in the muscle at rest and as the muscle contracts.
What is an EMG test used to diagnose? An EMG can detect abnormalities in the muscle or the nerves supplying it. This can aid in the diagnosis of nerve disorders (e.g. carpal tunnel syndrome, nerve root damage, diabetic neuropathy, motor neurone disease etc.) and muscle disorders (e.g. fasciculations, fatiguability and weakness).
Single Fibre Electromyography
This EMG technique records action potentials from two or more single muscle fibres simultaneously. The test is highly sensitive in detecting disturbances in neuromuscular transmission for disorders such as myasthenia gravis.
How to prepare.
DO
- Wear a sleeveless top (such as a camisole or vest) and/or shorts (depending on the limb being assessed).
- Please let us know if you are on any blood thinners or have a skin infection.
DON’T
- Apply lotion or moisturisers on the day of the appointment.
