EMG / NCV
General · N/A
Available at 0 labs
No lab currently offers this test.
About this test
What is EMG/NCV?
Electromyography (EMG) and Nerve Conduction Velocity (NCV) are diagnostic tests that assess the electrical activity of muscles and the speed of nerve signals. They help determine if nerves or muscles are damaged or not functioning properly.
Key Parameters
| Parameter | What it shows |
|---|---|
| Motor conduction velocity | Speed of signals from nerve to muscle |
| Sensory conduction velocity | Speed of signals from skin to spinal cord |
| Compound muscle action potential (CMAP) | Strength of muscle response |
| F-wave latency | Function of the entire nerve pathway |
| Needle EMG amplitude & recruitment | Muscle fiber health and innervation |
Why is it done?
- Evaluate weakness, numbness, tingling, or muscle cramps.
- Diagnose peripheral neuropathies, radiculopathies, myopathies, and nerve entrapments.
- Monitor progression of neuromuscular diseases.
- Guide treatment plans and surgical decisions.
Early Detection
This test can help identify signs of conditions such as carpal tunnel syndrome, Guillain‑Barré syndrome, or muscular dystrophy, but it does not diagnose on its own. A clinician interprets the results alongside symptoms, history, and other investigations.
What abnormal results may indicate
- Slower conduction velocities or absent responses suggest nerve damage or demyelination.
- Reduced CMAP amplitude or abnormal needle EMG patterns point to muscle disease or axonal loss.
- However, factors like hydration, temperature, medications, or recent exercise can influence readings.
Who might be advised to get this test?
Patients with unexplained muscle weakness, persistent numbness/tingling, foot drop, or suspected nerve compression. It is also used in follow‑up of known neuromuscular disorders.
Summary
EMG/NCV measures how well nerves and muscles communicate. It is a key tool for diagnosing and monitoring neuromuscular disorders, but results must be interpreted by a healthcare professional.
Used for detecting / monitoring
Before your test
Preparation
- Fasting: Not required for EMG/NCV.
- If combined with fasting tests: Follow the strictest fasting instruction (usually 8–12 hours).
- Medications: Continue routine meds unless your doctor advises otherwise.
- Hydration: Drink plenty of water the day before.
- Avoid alcohol & strenuous exercise 24 hrs prior.
Procedure
- The technician will locate the nerve or muscle to be tested.
- A small needle electrode is inserted into the muscle (minimal discomfort, similar to a quick pinprick).
- For NCV, a surface electrode is placed on the skin; a mild electrical stimulus is delivered.
- The test usually takes 30–60 minutes.
What to Expect
- Mild tingling or brief muscle twitching during needle insertion.
- No significant pain; the procedure is brief.
Note: Confirm specific preparation with your doctor or lab. This information is educational and not a substitute for professional medical advice.
Sample type: N/A
Report parameter guide
Motor Conduction Velocity
Speed at which electrical impulses travel along a motor nerve
Low: can indicate nerve damage, demyelination, or compression
High: can indicate hyperexcitability or technical artifact
Sensory Conduction Velocity
Speed of electrical impulses along a sensory nerve
Low: can indicate sensory nerve damage, demyelination, or compression
High: can indicate hyperexcitability or technical artifact
Compound Muscle Action Potential (CMAP) Amplitude
Size of the electrical response from a muscle after nerve stimulation
Low: can indicate muscle fiber loss, axonal loss, or neuromuscular junction disorder
High: can indicate hyperexcitability or technical artifact
Sensory Nerve Action Potential (SNAP) Amplitude
Size of the electrical response from a sensory nerve after stimulation
Low: can indicate sensory axonal loss or demyelination
High: can indicate hyperexcitability or technical artifact
Motor Latency
Time from nerve stimulation to the start of the muscle response
Low: can indicate conduction block or severe demyelination
High: can indicate demyelination, nerve compression, or metabolic neuropathy
Sensory Latency
Time from nerve stimulation to the start of the sensory response
Low: can indicate conduction block or severe demyelination
High: can indicate demyelination, nerve compression, or metabolic neuropathy
F-wave Latency
Time from stimulation to the return of a late motor response
Low: can indicate proximal nerve dysfunction or demyelination
High: can indicate demyelination, proximal nerve compression, or metabolic neuropathy
Motor Unit Potential Amplitude
Size of the electrical signal from a single motor unit during EMG
Low: can indicate motor neuron loss or muscle fiber loss
High: can indicate reinnervation, hyperexcitability, or technical artifact
Motor Unit Potential Duration
Length of time a motor unit potential lasts
Low: can indicate early reinnervation or technical artifact
High: can indicate chronic denervation and reinnervation or demyelination
Recruitment Pattern
Number of motor units activated at increasing muscle contraction levels
Low: can indicate motor neuron disease or severe neuropathy
High: can indicate hyperexcitability or technical artifact