What EMG and NCS can help evaluate
Symptoms such as tingling, numbness or weakness can originate from a peripheral nerve, nerve root, muscle or another part of the nervous system. Electrodiagnostic testing helps narrow the possibilities.
Nerve conduction studies (NCS) measure the response of selected nerves after brief electrical stimulation through surface electrodes. Needle electromyography (EMG) samples electrical activity in selected muscles. They are related tests, but they answer different parts of the clinical question and are not always both required.
When the test may be considered
Carpal tunnel syndrome
Hand numbness, tingling or weakness suggesting median nerve compression at the wrist.
Radiculopathy
Selected cases of arm or leg symptoms that may arise from a cervical or lumbar nerve root.
Peripheral neuropathy
Length-dependent numbness, burning or weakness affecting multiple nerves.
Focal nerve injury
Symptoms following trauma, sustained pressure or another possible local nerve lesion.
Muscle disease
Selected patterns of weakness where a muscle disorder is part of the differential diagnosis.
Unexplained weakness
Testing can contribute when clinical examination suggests a peripheral nerve or muscle process.
What happens during EMG/NCS?
Clinical review
Your symptoms, examination, referral question, medical history and previous reports are reviewed.
Nerve conduction study
Surface electrodes record responses while brief electrical pulses stimulate selected nerves. You may feel a short tapping or tingling sensation.
Needle EMG, if indicated
A fine recording electrode is placed into selected muscles. You may be asked to relax and then gently activate the muscle.
Interpretation
The pattern is interpreted in the context of the clinical question. The extent and duration of testing vary according to what needs to be examined.
How to prepare for your test
- Keep the skin clean and avoid lotion, cream or oil on the area on the day of testing.
- Wear loose clothing that allows the relevant arm or leg to be examined.
- Bring your referral, imaging, laboratory reports and previous EMG/NCS results.
- Bring a current medicine list.
- Tell the clinic in advance if you take blood thinners, have a bleeding disorder, pacemaker or implanted electrical device.
- Continue regular medicines unless your treating physician gives different instructions.
EMG/NCS FAQs
What is the difference between EMG and NCS?
NCS evaluates how electrical signals travel along selected nerves using surface electrodes. Needle EMG records electrical activity in selected muscles. The physician decides which components are needed for the clinical question.
Is EMG/NCS painful?
NCS involves brief electrical pulses and needle EMG uses a fine electrode in selected muscles, so temporary discomfort can occur. Tell the physician if you are anxious or particularly sensitive.
How long does the test take?
The duration varies with the number of nerves and muscles that must be evaluated. Ask when booking if you need help planning your visit.
Can EMG/NCS diagnose every cause of numbness?
No. Some conditions may not be detected by electrodiagnostic testing, and results must be considered with the examination and other tests.