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The flashcards below were created by user
jollyvulcan
on FreezingBlue Flashcards.
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What non-pathologic factors can a affect nerve conduction velocities?
- Tempetature
- Age (CV 1/2 normal at birth while Amp dec c/ age)
- Length of segment and height
- Gender
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What is an F-wave?
- Response elicited from any motor nerve with supramaximal stimulation
- Created by antidromic conduction which triggers a back-firing response
- Does not involve a synapse
- Abnormalities are seen as an early pathologic finding in demyelinating neuropathies like AIDP / CIDP
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What is an H Reflex?
- Can only be elicited in the tibial nerve in response to a submaximal stimulus
- It is the electrical equivalent of the ankle jerk reflex (S1) and measures the integrity of the entire reflex arc
- Monosynaptic in the cord
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What are the two basic patterns of pathology in a nerve conduction study?
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What are the features of axonal loss?
- Reduced CMAP (motor) and SNAP (sensory) amplitudes
- Mildy Reduced CV due to a loww of the fastest conducting fibers (not below 75% of normal)
There is no change in the distal motor latency, F-wave, conduction block, or abnormal temporal dispersion.
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What are some pathologic processes which might cause an a pattern of axonal loss on nerve conduction study?
- Axonal Neuropathies
- Nerve Trauma
- Motor Neuron Diseases
- Radiculopathies (CMAPs only)
- Secondary axonal loss in a primarily demyelinating process
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What are the features of demyelination?
- Substantial increases in CV (conduction velocity) which may be noted as:
- - Decreased CV in motor units (<70% nl)
- - Prolonged distal motor latencies (>130% nl)
- - Prolonged F-waves (>130% nl)
Conduction Block / Abnormal Temporal Dispersion
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Define Conduction Block ...
- A decrease in the amplitude of a proximal response relative to that of the distal response without an increase in the response duration.
- Reflects the block of conduction through a subset of motor axons in the nerve resulting from segmental demyelination.
- Must be at least a 30% decrement but often exceeds 50%
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What NCS phenomenon is depicted here ...
Conduction Block
There is a reponse to distal but not proximal stimulation indicating a segmental, demyelinating process.
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What is Temporal Dispersion?
- An abnormal prolongation of the motor response.
- Reflects the desynchronization of components of the response due to different conduction velocities along the length of the nerve
- >30% increase in dispersion is typically abnormal
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What NCS phenomenon is depicted here ...
Temporal Dispersion
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After an acute nerve injury, which amplitudes (SNAP or CMAP) are affected first?
CMAP
- Normal for 2-3 days
- Decline over 3-6 days
- Disappear by 7 days
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After an acute nerve injury, how long does it take to seen the maximal extent of axonal loss?
10 days
- Maxiaml decline in CMAPs are seen at 5-7 days
- Maximal decline in SNAPs are seen at 7-10 days
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What is the sequence of changes after an cute nerve lesion?
- Conduction Block across the site of injury (T0)
- No conduction across the site of injury (T0)
- Reduced Amplitudes on distal stimulation (T+7-10)
- Acute Denrvation (fibrillation portentials - T+14-35)
- Renervation (T+70-84)
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Define the term Insertional Activity?
It is the motor respnse generated by passing a needle through the muscle and typically last <20 ms
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What can cause an increased insertional activity?
Acute Denervation
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What can cause decreased insertional activity?
- Inexcitable Tissue (fibrosis, fatty replacement, ischemia)
- Physiologic Contractures (McArdle's, PFK)
- During an attack of periodic paralysis
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What are examples of abnormal sponaneous muscle activity?
- From Muscle:
- Fibrillation Potentials
- Positive Sharp Waves
- Complex Repetative Discharges
- Myotnic Discharges
- From Motor Neuron:
- Fasciculation Potentials
- Myokymia
- Neuromyotonia
- Tremor
- Cramp Discharges
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What are Fibrillation Potentials?
- Spontaneous firing of a single muscle action potential
- Diphasic with initial positivity (downward)
- Appear 2-4 weeks following:
- - Denervation
- - Neuropathy
- - Myopathy
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 What EMG finding is demonstrated here?
Fibrillation Potentials
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What are Complex Repetative Discharges?
- A train of grouped muscle fiber action potentials
- Fire in a regular, lock-step, drumming fashion
- Begin and end abruptly
- Seen in any muscle disease
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What are myotonic discharges?
- These are repetative discharges provoked by passage of the needle through the muscle or percussion
- Train of muscle fiber action potentials with a waxing and waning frequency / amplitude ("dive bomber")
- Seen in hereditary myotonias, periodic paralysis, and some toxic / metabolic myopathies
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 What EMG phenomenon is depicted here?
Complex Repetative Discharges
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 What EMG phenomenon is depicted here?
Myotonic Discharges
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What are Fisciculation Potentials?
Spontaneous motor neuron discharge leading to the appearance of an action potential (MUAP) but slower
- Many causes:
- - Neurogenic Diseases
- - Cholinesterase Inhibitors
- - Benign Fascics / Cramps-Fasciculation Syndrome
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What is Myokymia?
- Repeating discharges of groups of MUAP’s which have the appearance of grouped fasciculations.
- Bursts repeat at regular or semiregular intervals
- Variety of causes:
- - Facial: MS, Brainstem Lesions
- - Limb: radiation plexopathies
- - General: Isaac's SYndrome
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What is a normal conduction velocity in an upper extremity in an adult?
50 msec
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What is a normal conduction velocity in the lower extremity of an adult?
40 msec
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