Nerve Conduction Studies and EMG: What to Expect and What They Show

Numbness, tingling and weakness can come from a trapped nerve, nerve damage or a muscle problem. Nerve conduction studies and EMG help pinpoint where the problem is and how severe it is.

Imagine waking at night with tingling, numb fingers that you have to shake to bring back to life. Your healthcare provider suspects carpal tunnel syndrome and books a nerve conduction study before deciding whether you need surgery.

What these tests are

A nerve conduction study (NCS) measures how fast and how strongly electrical signals travel along your nerves. Electromyography (EMG) records the electrical activity of your muscles. The two tests are often done together, by a neurophysiologist or specially trained healthcare provider.,Together, they can show whether nerves are compressed, damaged or working normally, and whether weakness is coming from a nerve or the muscle itself.

Common reasons for testing

• Carpal tunnel syndrome and other trapped nerves, such as at the elbow (cubital tunnel)
• Peripheral neuropathy, for example from diabetes
• Nerve root problems from the spine, such as sciatica
• Unexplained weakness, muscle wasting or cramps
• Some muscle diseases and motor neurone disease
• Nerve injuries

How to prepare

• Have a bath or shower and do not use creams or lotions on the day
• Keep your hands and feet warm, as cold can affect results
• Wear loose clothing that allows access to your arms and legs
• Tell the team if you have a pacemaker or defibrillator, take blood thinners or have a bleeding disorder
• You can usually eat and take your medicines as normal

What a nerve conduction study feels like

Sticky electrodes are placed on the skin over the muscles or nerves being tested. A small device then gives brief electrical pulses to the nerve at different points. Each pulse feels like a quick tap or a small static shock and may make your muscle twitch.,Most people find it slightly uncomfortable but tolerable. The test usually takes 15 to 60 minutes, depending on how many nerves are tested.

What EMG feels like

For an EMG, a very fine needle electrode is inserted into a muscle to record its activity at rest and when you gently tighten it. You may feel a sharp prick when the needle goes in and some aching during the test. A new sterile needle is used for each person.,You may have mild soreness or small bruises afterwards, which settle within a day or two.

Understanding results

• Slowed conduction across a specific point: suggests nerve compression, such as at the wrist in carpal tunnel syndrome
• Reduced signals along many nerves: suggests peripheral neuropathy
• Abnormal muscle activity on EMG: can indicate nerve damage affecting that muscle, or a muscle disease
• Results are graded as mild, moderate or severe, which helps decide treatment, such as splints, injections or surgery for carpal tunnel syndrome

Carpal tunnel syndrome treatment options

• Wrist splints worn at night
• Avoiding activities that make symptoms worse
• Steroid injections
• Carpal tunnel release surgery for moderate to severe or persistent cases
• Treating related conditions such as an underactive thyroid or diabetes

Peripheral neuropathy: protecting your feet

If tests show nerve damage in your feet, for example from diabetes, you may not feel injuries. Check your feet daily for cuts, blisters or colour changes, wear well-fitting shoes, never walk barefoot, test bath water with your elbow and attend regular foot checks. Seek help quickly for any wound that is not healing.

Questions to ask about your results

• Which nerves are affected, and how severely?
• Is the problem from compression, nerve damage or the muscle?
• What treatment do you recommend?
• Will I need repeat testing?

Frequently asked questions

Is it safe with a pacemaker?

Often yes, with precautions. Always tell the team beforehand.

Can I drive home?

Yes, usually.

How soon will I get results?

The person doing the test may explain initial findings, with a full report sent to your healthcare provider.

But the shocks sound frightening

The pulses are very brief and adjusted to the lowest effective strength. You can ask the team to pause at any time.

Related: Carpal tunnel syndrome · Numbness and tingling

Sources: British Society for Clinical Neurophysiology, American Association of Neuromuscular and Electrodiagnostic Medicine, National Institute for Health and Care Excellence, NHS.