Nerve conduction study at Brighton Hospital

What is a nerve conduction study?

A nerve conduction study (NCS) is a test that measures how well electrical signals travel along your nerves. It helps show whether a nerve is damaged, compressed or affected by disease, and how severe the problem might be.

Why might I need one?

Your doctor may suggest a nerve conduction study if you have symptoms such as:

• numbness or tingling in your arms, legs, hands, feet or face
• muscle weakness
• muscle cramps, spasms or twitching.

It can help diagnose nerve compression syndromes, such as carpal tunnel syndrome or sciatica, and peripheral neuropathy (damage to the nerves outside your brain and spinal cord), which can have many causes including diabetes, vitamin deficiencies, thyroid problems, certain autoimmune conditions, infections, some medicines, or a direct injury to a nerve.

A nerve conduction study is often done alongside a separate test called electromyography (EMG), which looks at your muscles rather than your nerves. Doing both together helps your doctor work out whether your symptoms are coming from a nerve problem, a muscle problem, or both.

What are the benefits of having it?

A nerve conduction study can pinpoint roughly where along a nerve a problem lies, by testing the nerve's response at different points. This helps your doctor understand the cause, severity and likely outlook of your symptoms, and plan the right next steps, without needing surgery or an invasive procedure.

Are there different types of the test?

Nerve conduction studies can look at two different types of nerve, depending on your symptoms:

• motor nerves, which control your muscles and movement
• sensory nerves, which carry information to your brain about things you touch, feel or sense.

Your doctor may test one or both types. Depending on what they find, you may also need an EMG straight afterwards, though not everyone requires this.

How do I prepare for the test?

Before your appointment:

• bathe or shower as normal, and wear comfortable, loose-fitting clothing so the area being tested is easy to access
• avoid using cream, lotion or perfume on your skin beforehand, since these can affect the test's accuracy
• tell your doctor if you have a pacemaker, implanted defibrillator, or similar device
• tell your doctor if you take blood-thinning medication.

You can eat, drink and take your usual medicines as normal, unless you're told otherwise.

What happens during the test?

1. You'll sit or lie down, usually on a table, bed, or reclining chair.
2. The skin over the nerve being tested is cleaned.
3. Small electrode pads are stuck to your skin above the nerve.
4. A brief electrical pulse, lasting a fraction of a second, is sent through the pad to stimulate the nerve. You'll feel a brief tap or tingling sensation, similar to a TENS machine.
5. Other electrodes record how quickly and strongly the signal travels along the nerve.
6. This is repeated at different points, and for different nerves, depending on your symptoms.

If an EMG is also needed, this is usually done straight afterwards: a fine needle electrode is inserted into the muscle to record its natural electrical activity, both while it's relaxed and while you tense it.

A nerve conduction study on its own can take anywhere from 15 minutes to an hour, depending on how many nerves are tested. If an EMG is added, the whole appointment may take longer.

What happens after the test?

You can usually go home straight away afterwards.

A nerve conduction study alone doesn't usually give an instant diagnosis. Your results are considered alongside your symptoms, medical history and any other tests. The report is typically sent to the doctor who referred you within a couple of days, though you may not discuss the results with them until your next appointment, which could take a little longer to arrange.

If you also had an EMG, the muscles that were tested may feel sore for a day or so, and there may be some minor bruising where the needle was inserted.

What are the risks or side effects?

Nerve conduction studies are generally very safe. The electrical pulses can feel uncomfortable, a bit like mild static electricity or a TENS machine, and may briefly increase your usual symptoms for a few minutes, but this settles quickly and shouldn't cause any lasting harm.

If an EMG is also carried out, you may feel a sharp scratch as the needle goes in, and the muscle may be sore or bruised afterwards for a short time.