Nerve Conduction Study Overview

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Questions and Answers

Which of the following is a common disorder associated with peripheral neuropathy?

Myasthenia gravis

Congenital myopathy

Radiculopathy

Diabetic neuropathy (correct)

What is the primary purpose of the electrodes in the NCS procedure?

To measure the electrical current in the nerve pathway (correct)

To deliver anesthesia during the test

To stimulate nerves using high voltage

To clean the skin before testing

What does a longer latency time in a motor nerve conduction study indicate?

Presence of an artificial pacemaker

Slower and weaker current due to nerve damage (correct)

No impact on nerve conduction

Improved nerve function

Which component is NOT part of the NCS?

Electromyography (EMG) Signup and view all the answers

What is a common complication associated with the NCS procedure?

Discomfort from the electrical current Signup and view all the answers

What does the amplitude of a nerve response signify?

The strength of the response measured in millivolts Signup and view all the answers

What limitation exists in evaluating lesions using nerve conduction velocity (NCV)?

It cannot differentiate between pre- and postganglionic lesions Signup and view all the answers

Which statement correctly describes the characteristics of sensory nerve conduction studies (NCS)?

Sensory latencies are measured in milliseconds. Signup and view all the answers

How is the sensory nerve conduction velocity (NCV) calculated?

By measuring the distance between the stimulating and recording electrode and the latency Signup and view all the answers

What is a key characteristic of sensory action potentials (SNAPs) compared to compound muscle action potentials (CMAPs)?

SNAPs are typically more sensitive in detecting incomplete peripheral nerve injuries Signup and view all the answers

What does the amplifier in an EMG machine primarily do?

Pick up small potentials and amplify them Signup and view all the answers

What range of sensitivity is typically used for motor nerves in an EMG system?

1000-5000 μV Signup and view all the answers

What is the primary purpose of a nerve conduction study (NCS)?

Assess the function of motor and sensory nerves Signup and view all the answers

Which frequency range is used for the frequency filter selection of motor nerves in EMG?

10-10000 Hz Signup and view all the answers

Which symptom is typically indicative of nerve damage, warranting a nerve conduction study?

Numbness and tingling Signup and view all the answers

Study Notes

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.

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Description

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.