Electromyography (EMG) & NCS
Electromyography (EMG) and Nerve Conduction Studies (NCS) are complementary electrophysiological tests that evaluate the function of muscles and peripheral nerves.
Duration
30-90 minutes
Discomfort
Mild tingling / pricks
Safety
Generally safe
Description
Electromyography (EMG) and Nerve Conduction Studies (NCS) are complementary electrophysiological tests that evaluate the function of muscles and peripheral nerves. EMG measures electrical activity in muscles, while NCS measures how quickly nerves transmit electrical signals.
Purpose & Uses
- Diagnosis of nerve damage or neuropathy
- Evaluation of muscle weakness or atrophy
- Detection of neuromuscular junction disorders
- Assessment of carpal tunnel syndrome
- Evaluation of peripheral nerve injuries
- Investigation of muscle pain or cramping
- Diagnosis of motor neuron diseases (ALS)
- Assessment of radiculopathy (nerve root compression)
NCS Types
- Motor NCS: Measures conduction velocity and amplitude of motor nerves
- Sensory NCS: Measures conduction velocity and amplitude of sensory nerves
- H-Reflex and F-Wave: Tests of nerve conduction in proximal segments
EMG Techniques
- Needle EMG: Small needle electrode inserted into muscle to record activity
- Surface EMG: Electrodes placed on skin surface over muscle
Procedure Steps
Nerve Conduction Study
- Electrodes are placed on skin over the nerve
- Electrical stimulation is applied to the nerve
- Response is recorded from another electrode location
- Multiple nerves and recording sites are tested
- Procedure is repeated with different stimulus intensities
Electromyography
- Patient is positioned comfortably
- Small needle electrode is inserted into muscle
- Electrical activity is recorded at rest and during muscle contraction
- Multiple muscles are tested
- Needle is withdrawn and skin is cleaned
Results Interpretation
NCS Results
Normal: Appropriate conduction velocity and amplitude
Abnormal: Slowed conduction, reduced amplitude, or conduction blocks suggesting nerve damage
EMG Results
Normal: Appropriate motor unit action potentials
Abnormal: Denervation potentials, myopathic patterns, or neuromuscular junction dysfunction
Quick Links
Preparation
- • Avoid strenuous exercise for 2-3 days before test
- • Avoid caffeine and stimulants on day of test
- • Wear loose, comfortable clothing
- • Inform technician of any bleeding disorders or anticoagulant use
- • Bring list of current medications