Nerve conduction study (NCS)
A nerve conduction study is a diagnostic test undertaken to assess function and integrity of the peripheral nerves including the motor, sensory and the autonomic nerves. It involves activating nerves with small (safe) pulses of electrical current over several points on the skin (occasionally under the skin using very fine depth/needle electrodes) and measuring responses which allows us to calculate the integrity of the nerves and the speed with which they conduct signals.
This is often complemented by electromyography (EMG) used to study muscles and the nerve-muscle interface (neuromuscular junction). This measures the electrical activity in your muscles. It is often done at the same time as a nerve conduction study. Both tests can help us identify the presence, location, and extent of diseases that affect nerves and muscles or the nerve-muscle interface called the neuromuscular junction.
Why will I need a nerve conduction study?
A wide variety of neurological conditions are assessed using a nerve conduction study frequently complemented by a needle electromyography (EMG). It is used to investigate complaints of numbness, tingling, shooting pain, muscle twitching and weakness which could stem from a pinched nerve caused by a herniated disc (radiculopathy), nerve entrapment (carpal tunnel, tarsal tunnel & cubital tunnel syndrome), degenerative neurological conditions (motor neurone disorders, spinal muscular atrophy etc), common disorders of the peripheral nerves (peripheral neuropathy) and inflammatory conditions such as Guillain Barre syndrome or Chronic Inflammatory Demyelinating Polyneuropathy (CIDP).
It is helpful in diagnostic evaluation of many disorders (and more) such as:
- Carpal tunnel syndrome,
- Hereditary neuropathies (Charcot-Marie-Tooth, Hereditary Neuropathy with Pressure Palsies / HNPP),
- Disorders of motor neurons (ALS/SMA),
- Autonomic dysfunction,
- Peripheral neuropathy, and
- Inflammatory neuropathies such as vasculitic neuropathy or Chronic Inflammatory Demyelinating Polyneuropathy (CIDP).
What are the risks associated with a NCS/EMG?
The strength of electrical signals used during an NCS is extremely low and in the order of milliamperes. There are no long-term risks associated with this procedures. Please speak to the technician or your doctor before the procedure if you have any questions. It may be necessary to sign a consent form before the procedure.
Specific conditions may need special precautions such as an implanted cardiac defibrillator or a pace-maker. If you have any of these, please advise the technician or staff prior to procedure.
If you are in severe pain or if you take blood thinners like warfarin, clopidogrel, dabigatran, apixaban or rivaroxaban for a clotting disorder, please advise the doctor or your technician so that precautions can be undertaken if a needle EMG examination is necessary.
How do I prepare for a NCS/EMG test?
The procedure will be usually discussed by the technician or the neurologist but please feel free to ask any questions before or during the test.
- A consent form will have to be signed before the procedure.
- You can bring one support person during the test. It may however depend on Public Health Orders applicable at the time and vaccination status considering the pandemic situation.
- It is not necessary to fast before the procedure.
- It is advisable to avoid using any moisturising creams or lotions or hair-gel before the procedure.
- Wear loose-fitting clothes but occasionally a disposable gown may be provided.
- This procedure does not involve sedation.
- It is not necessary to stop your usual medications before the test unless you have been specifically advised before the test (some testing such as repetitive nerve stimulation studies may require that you stop Mestinon/pyridostigmine as advised by the doctor prior to your procedure).