Step-by-Step Explanation of What to Expect During Nerve Conduction Testing
Nerve conduction studies (NCS) are usually performed first during an EMG/NCS testing session. Understanding what happens during NCS can help reduce anxiety and prepare you for what to expect. This article walks you through the procedure step-by-step.
[1] NCS (nerve conduction studies) measures how fast electrical signals travel along nerves. The test evaluates the speed of conduction and the strength of the nerve's response. This information helps determine if nerves are functioning properly or if there's damage, compression, or disease.
NCS is typically performed BEFORE EMG in a combined testing session. While EMG measures muscle electrical activity, NCS measures nerve electrical activity.
[2] NCS uses small surface electrodes placed on your skin—no needles are involved. These electrodes are:
Two electrodes are placed for each nerve being tested:
[3] The basic principle is simple:
The electrical stimulus is carefully controlled:
Safety note: The stimulus is designed to be uncomfortable but not painful or dangerous.
The technician chooses which nerves to test based on your symptoms. Common nerves tested include:
The technician cleans your skin and places small surface electrodes at precise locations over the nerve. The electrodes are stuck to your skin with mild adhesive and conductive gel.
[1] A small electrical pulse is applied to the nerve through a stimulating electrode. The technician gradually increases the intensity until a clear response is recorded.
What you feel: A tingling sensation or mild electrical shock. The sensation is brief and localized to the area being stimulated.
The recording electrodes capture the nerve's electrical response. The computer displays and measures:
For each nerve, stimulation may be applied at multiple locations to measure conduction velocity between different points along the nerve. This helps identify where any problem might be located.
How fast the nerve signal travels. Measured in meters per second. Normal values typically range from 40-60+ m/s depending on the nerve. Slower than normal suggests nerve damage or compression.
The strength of the nerve's electrical response. Measured in millivolts. Reduced amplitude suggests loss of nerve fibers (axonal damage). Very reduced amplitude might indicate many dead nerve fibers.
Time for the signal to travel a specific distance. Abnormally prolonged latency suggests slowing of conduction, often from demyelination (loss of nerve insulation).
Tests motor nerves that control movement. Recording electrodes are placed over muscles. The response measured is the muscle's electrical response to nerve stimulation.
Tests sensory nerves that carry sensation. Recording electrodes are placed directly over the nerve itself. The response measured is the nerve fiber's own electrical activity.
Clinical note: Sensory nerves are often affected first in neuropathy, so sensory NCS can detect problems earlier than motor NCS.
[2] Depending on your symptoms, multiple nerves may need testing. The process repeats for each nerve:
NCS typically takes 15-20 minutes, depending on how many nerves are tested. The entire EMG/NCS session (NCS plus EMG) typically takes 30-60 minutes.
[3] Most people describe NCS discomfort as:
The electrical stimulation must be strong enough to activate the nerve completely. Higher stimulus intensity is needed than you might expect, which is why the sensation can be uncomfortable. However, the discomfort is brief and localized.
NCS is usually less uncomfortable than EMG. While NCS involves electrical stimulation (mild discomfort), EMG involves needle insertion (brief sharp sensation). Most patients find NCS more tolerable than EMG.
This article is educational information only and does not constitute medical advice. The information here is based on current medical literature and professional standards but is not a substitute for professional medical evaluation, diagnosis, or treatment. Always consult with your healthcare provider regarding your specific medical situation, symptoms, and questions about sleep studies or any medical procedure.