introduction to electrodiagnostic testing Flashcards
what are electrodiagnostic studies?
assess physiology of nerve and muscle
always considered an extension of the physical examination
include nerve conduction studies and electromyography
assists in diagnosis of peripheral nerve lesions and or muscle injury
why perform electrodiagnostic studies?
establish correct diagnosis
localize lesion
determine treatment
provide information on prognosis
what are some disorders of the PNS?
motor neuronopathy (ALS, SMA, poliomyelitis)
radiculopathy
plexopathy (cervical, lumbrosacral)
neuropathy (entrapment, polyneuropathy)
neuromuscular junction disorder (myasthenia gravis, lambert-eaton syndrome, botulism)
myopathy
what takes place in the electrophysiological assessment?
subjective information
physical examination
develop working hypothesis
explain procedures and get informed consent
position patient
perform test (NCS, EMG)
interpret data
write report
what is the NCS: waveform analysis?
measure largest diameter, fastest conducting myelinated fibers
evoked potentials from sensory fibers: sensory nerve action potential (SNAP)- orthodromic or antidromic
evoked potentials from muscle: compound motor action potential (CAMP)- orthodromic
describe the evoked potential
shape
amplitude (summation of all fibers depolarize, measured baseline to negative)
duration
rise time
area
latency
nerve conduction velocity (speed=distance/time)
what are NCS abnormalities?
demyelinating pathology (increased latency, decreased NCV, conduction block)
axonal pathology (decreased amplitude)
what 4 parts of clinical findings and results from NCV does needle electromyography depend on?
insertional activity
examination of muscle at rest
motor unit analysis
recruitment
what is insertional activity?
brief electrical activity associated with needle movement (normal: 150-300 milliseconds)
muscle fiber being depolarized by needle insertion
healthy muscle is electrically silent once needle movement stops
crisp sounf
what is decreased insertional activity?
needle is inserted into atrophied muscle
putting a needle into sand
<150 milliseconds
what is increased insertional activity?
muscle pathology
presence of positive sharp waves (PSWs) ad fibrillation potentials on insertion that DO NOT LAST
> 300 milliseconds
how should muscles be at rest?
silent
if there is spontaneous activity when examining a muscle at rest what does this mean?
typically abnormal
after injury or denervation, membrane becomes more + due to increased Na in damaged muscle (positive sharp waves, fibrillations, complex repetitive discharges, myotonic discharges)
what are components being analyzed when the patient is asked to minimally contract the muscle being tested?
amplitude
rise time
duration
phases
what is amplitude?
the size of the MUAP, measured from peak to peak
