NCV/EMG

Question 1

what does a nerve conduction study evaluate

Answer 1

evaluate the function of peripheral nerves, NMJ, and muscle fiber innervation

Question 2

what does a nerve conduction study measure?

Answer 2

speed of conduction
size of action potential

Question 3

what does EMG evaluate?

Answer 3

muscle function and electrical activity at rest and during contraction

Question 4

what does EMG measure

Answer 4

shape, size, duration, prescence/absence of action potentials generated in the muscle

Question 5

what do SEPs evaluate?

Answer 5

CNS evaluation of sensory changes

Question 6

SEPs measure:

Answer 6

potentials generated in CL somatosensory cortex

Question 7

can electrophysiologic testing be used to diagnose conditions?

Answer 7

No! Used in differential as an objective finding to refute or support but not confirm diagnosis

Question 8

equipment needed for NCV

Answer 8

electrodes
differential amplifiers
oscilloscope (NCV/EMG)/speaker (EMG)
processing unit
stimulating electrode to elicit response

Question 9

what EMG findings should there be at rest?

Answer 9

none, electrical activity should be quiet

Question 10

latency

Answer 10

time it takes from the stimulus to get a response
traveling a farther distance down the nerve will result in a longer latency
use to calculate nerve conduction speed

Question 11

distal sensory latency

Answer 11

measure most peripheral part of nerve to detect impairment in any part of the nerve, proximal or distal, by seeing if speed is impaired

Question 12

distal motor latency

Answer 12

longer latency than sensory because signal has to cross the NMJ and propagate throughout the fiber

Question 13

H reflex testing in NCV

Answer 13

test normal reflex arc with NCV

Question 14

what does repetitive stimulus testing in NCV assess?

Answer 14

NMJ issues such as myasthenia gravis

Question 15

what areas can EMG assess?

Answer 15

AHC
intervertebral foramen compression
muscle

Question 16

how can EMG assess AHC?

Answer 16

diseased AHC can cause axons to die leading muscle fibers to be irritable
abnormal activity will be produced including positive sharp waves and fibrillation potentials

Question 17

how can EMG assess nerve compression?

Answer 17

nerve compression would result in multiple muscles having abnormal electrical findings in a myotomal pattern

Question 18

how can EMG assess muscle function?

Answer 18

it can find abnormal size and duration of signals in conditions like duchene MD

Question 19

EMG norms?

Answer 19

no norms, have to compare to pt’s baseline

Question 20

demyelination

Answer 20

damage to the myelin sheath decreasing speed of AP
caused by DM, carpal tunnel

Question 21

axonopathy

Answer 21

part of the potential pool of axons no longer function
speed is normal but amplitude of response is diminished
amplitude is normally summation of all axons firing

Question 22

acute compression of nerve

Answer 22

pressure on peripheral nerves can create ischemia and transient demyelination that quickly reverses once blood supply to nerve is recovered

Question 23

neuropraxia

Answer 23

discrete demyelination without loss of axon continuity
causes stopping or slowing of conduction over lesion
lowest level of nerve injury, least threatening

Question 24

wallerian degeneration

Answer 24

process of repairing broken axon and myelin by degenerating damaged tissue and replacing it distal to proximal slowing, 1-2 mm a day

Question 25

s/s of neuropraxia

Answer 25

paralysis/marked reduction in muscle strength reduced or absent sensation

Question 26

NCV results of neuropraxia

Answer 26

increased latency in area with normal velocity above and below normal EMG at rest

Question 27

axontomesis

Answer 27

caused by severe compression/stretch loss of axonal continuity but endoneurial connective tissue sheath is intact results in Wallerian degeneration after 48 hours sheath guides regenerating axon

Question 28

s/s after axontomesis

Answer 28

total loss of function until nerve regenerates worse prognosis with possible incomplete end innervation

Question 29

NCV results after axontomesis

Answer 29

if large axons intact, speed will be normal but amplitude will decrease If large not intact, speed will decrease as well

Question 30

EMG results after axontomesis

Answer 30

fibrillation potential, positive sharp waves for 2-3 weeks

Question 31

neurotmesis

Answer 31

loss of axonal and CT continuity from severence or stretch or crush partial: damage to endoneurial sheath and endoneural tissue complete: severed

Question 32

s/s of neurotmesis

Answer 32

complete loss of function no muscle activity likely needs surgery very poor prognosis

Question 33

NCV and EMG after neurotmesis

Answer 33

no conduction below lesion no spontaneous potentials on EMG these will not recover without surgical repair

Question 34

polyneuropathy

Answer 34

degeneration of distal ends of long axons along w myelin degeneration sensory loss first, then motor

Question 35

myelinopathy

Answer 35

segments of myelin lost due to infection/immune eg GBS decreased sensation, DTR

Question 37

GBS

Answer 37

normally good prognosis guarded prognosis if there is evidence of denervation on NCV partial innervation has better prognosis, will show slower conduction velocity

Question 38

myopathy findings

Answer 38

normal NCV fibrillations and sharp waves on EMG

Question 39

myotonia findings

Answer 39

delayed relaxation after contraction high frequency discharges repetitive on EMG mild NCV slowing