Nerve Conduction Study Overview

Nerve Conduction Study (NCS)

• NCS is used to evaluate motor and sensory nerve function.
• Nerve Conduction Velocity (NCV) is a measurement made during the test.

Uses of NCS

• Used to evaluate numbness, tingling, burning, and/or weakness in arms and legs.
• The specific type of study depends on the presented symptoms.
• Indications include symptoms of nerve damage, differentiating between nerve damage types, and determining the extent of nerve injury.

Common Disorders Diagnosed by NCS

• Peripheral neuropathy: Mononeuropathy (e.g., carpal tunnel syndrome), mononeuritis multiplex (e.g., vasculitis, rheumatoid arthritis, lupus, sarcoidosis, leprosy, Lyme disease, amyloidosis), polyneuropathy (e.g., diabetic neuropathy).
• Myopathy: Myotonia, congenital myopathies, metabolic myopathies, muscular dystrophies (e.g., Facioscapulohumeral muscular dystrophy).
• Radiculopathy: Nerve root damage from herniated discs.
• Neuromuscular junction diseases: Myasthenia gravis.

Procedure Description

• Electrodes: Skin is cleaned, electrodes are taped to the skin along the nerves being studied.
• Stimulus: A small electrical current activates nerves.
• Current: Electrodes measure the current traveling through the nerves.
• Damaged Nerve: If the nerve is damaged, the current will be slower and weaker.
• Procedure Time: Approximately 30-90 minutes.
• Complications: No reported major complications, but some discomfort from the electrical current is expected.
• Important Considerations: The test is not invasive, precautions are needed if an artificial pacemaker is present, anesthesia is not used, and no specific post-procedure precautions are required.

Components of NCS

• Compound Motor Action Potential (CMAP): Also called motor nerve conduction study.
• Sensory Nerve Action Potential (SNAP): Also called sensory nerve conduction study.
• F-wave study
• H-reflex study
• A-wave study
• Blink reflex study
• Direct Facial Nerve Study

Motor Nerve Conduction Study (Sites)

• Median nerves: Wrist and elbow (Abductor Pollicis Brevis)
• Ulnar nerves: Wrist and elbow (First Dorsal Interosseous, Abductor Digiti Minimi)
• Peroneal nerves: Ankle and head of fibula (Extensor Digitorum Brevis)
• Tibial nerves: Ankle (Abductor Hallucis)
• Other nerve locations: Sensory Nerves (R/L) at different locations

Sensory Nerve Conduction Study

• Measures sensory nerve conduction.
• Recording electrode is located proximal to the stimulating electrode.
• Amplitude is significantly smaller than motor potentials, usually in the microvolt (µV) range.
• NCV is calculated based on latency and distance between electrodes.
• Useful in localizing nerve lesions related to the dorsal root ganglion (DRG).
• Important in clinical presentations of sensory abnormalities.

F-wave Study

• Evokes a small, late response from a short duration, supramaximal stimulation.
• Initiates an antidromic motor response to the spinal cord, followed by an orthodromic motor response to the recording electrode.

H-reflex Study

• Creates a late response analogous to a monosynaptic reflex.
• Initiated with a submaximal stimulus at a longer duration.
• Preferentially activates IA afferent nerve fibers.

Interpretation of Nerve Conduction

• Nerve conduction speed is related to nerve diameter and myelination.
• Damaged nerves transmit signals more slowly and less strongly than healthy nerves.
• Typical conduction velocity range is 50-60 meters per second, but varies by individual and nerve.
• Changes in latencies and amplitudes can indicate pathological processes, such as slowed conduction velocity.
• Examples of findings: slowing of NCS, slowing across the wrist, indicating carpal tunnel syndrome.

This quiz explores the Nerve Conduction Study (NCS), a critical test used to evaluate motor and sensory nerve function. It covers the uses of NCS in diagnosing common disorders, including peripheral neuropathy and myopathy, as well as its indications and measurement techniques.