electrodiagnostic studies Flashcards
what are EMG used to determine? what tests does it include?
used to determine if theres a prob IN PERIPHERAL nervous system. if so where? can it be dx? **
EMG: electromyography
NCS: nerve conduction studies
EMG= can be used to describe both
they are extension of neurological and musculoskeletal examination
who performs electrodiagnostic studies
physiatrist, neurologist, physical therapists
why is important to do EDX? **
What are some reasons to use EDX
represents the PHYSIOLOGICAL CHANGES to the puzzle
**** Establish correct dx localize lesion determine tx provide info for prognosis
when should electrodiagnostic studies be performed
EMG/NCS should NOT be performed prior to 21 days–it takes about 21 days for the full injury to occur after injury or onset of symptoms; if you do it earlier may miss the pathology
failure of nerve conduction across the affected nerve segment combined w/ normal nerve conduction above and below the segment.
NO wallerian degeneration involved
Good prognosis
Neurapraxia
similar to “bruise” to nerve
Disruption of axon continuity with Wallerian degeneration but perineurium and/or endoneurium are still intact
axonotmesis
some disruption to axon
Neurotmesis
require nerve surgery
complete transection/severence through the nerve; carries poor prognosis and surgical repair is needed for functional recovery
endoneurium and perineurium disrupted
degenerative changes which occur in the distal axonal segments and their myelin sheath secondary to proximal axonal injury or death of cell body
Wallerian degeneration
what are the contraindication for electrodiagnostic studies
severe bleeding disorder(high INR)
NCS is contraindicated in patient with automated cardiac defibrillator
Cellulitis (skin/soft tissue infection)–due to infection
stimulation of peripheral nerve while recording from a muscle innervated by that nerve
motor nerve conduction (CMAP)
stimulation of cutaneous or mixed nerve while recording from a mixed or cutaneous nerve
sensory nerve conduction (SNAP)
latency:NCS
interval between onset of a stimulus and onset of response
Amplitude:NCS
max voltage difference between two points, it is proportional to the number and size of nerve fibers that are depolarized providing an estimate of the amt of nerve tissue that is electrically active
Tells how much info nerve is transmitting*
NCS: Conduction velocity
factors that affect conduction
what can decreased temp could affect?
Speed at which nerve fibers carry electrical stimulus between two sites
cV determines how many axons are conducting.
More useful for distal peripheral nerves
factors:
Age: infant=1/2 adult, 5 yrs=adult, 60=10% decline per decade
Temp: ideal of upper extremity is 32 deg C, and lower extremity of 30 deg C
Decrease temp:
prolong latency
INCREASED amp
decreased CV
what is most useful for detecting proximal nerve pathologies
late responses: F waves and H reflex
what response is usefult for detecting gullian barre syndrome
Late response: F wave
which reflex is Very good at distinguishing between S1 from L5 radiculopathies and often difficult with physical exam/EMG due to overlapping myotomes
how does it distinguish the two?
H reflex:monosynaptic spinal reflex
H reflex will be ABNORMAL in S1 radiculopathy
insertional response for EMG studies
- Insertional activity :
- increased: denervated muscle/myopathy
-normal/decreased: replacement of fat/connective tissue
=
spontaneous activity of EMG
when is it pathologic?
pathologic if abnormal electrical activity occurs at rest:
Fibrillation potential**
positive sharp waves,**
fasciculations potentials , myotonic dischrages, complex reptetitive discharges, myokymic dischrages, neuromyotonic discharges
voluntary activity in EMG
appearance of motor unit AP–one axon and all its muscle fibers
observe amplitude, duration, recruitment
Interpreting Normal EDX
does not necesssary mean normal function. just means that sensitivity and specificity of exam cannot define a specific problem by available technique
what is one of the most important physical findings that will continue onto NCS/EMG
Reflex loss or asymmetry: involuntary response should be reflexive regardless–with the loss would indicate neuro prob
If you suspect an L5 radiculopathy in your patient, what test would you order:
- for the best view of pathology?
- objectively demonstrate physiologic changes in nerve or muscle?
- pinched nerve: best test is MRI
2. EMG/NCS
which nerve root does H reflex travel on?
S1
How do you know if its L5 radiculopathy
H reflex is normal on both sides
what are the 2 main parts of EDX? and what are their functions?
NCS: nerve will be stimulated/shocked and recorded with surface electrodes (NO NEEDLE)!
EMG: NEEDLE electromyography: muscle membrane activity will be evaluated at rest with contraction with a needle inserted in muscle
Electrical activity recorded by needle electrode in muscle fibers firing
displays ‘real time’ picture and sounsd of electrical activity of the muscle membrane
NCS/EMG provide info about injusred or diseased nerve pathophysiology (demyelination vs axonal lsos, or complete severing of nerve)
this is just a PHYSIOLOGIC piece to puzzle, does not DX the cause!
Hypereflexia vs hyporeflexia damage where?
Central: HYPERreflexia
Peripheral: HYPO reflexia
atrophy is Central or peripheral nerve damage?
peripheral nerve damage
positive babinski indicates central or peripheral nerve damage:
CENTRAL
what are the symptoms and physical findings for NCS/EMG
Symptoms: numbness, tingling, pain, weakness
Physical findings: reflex loss or asymmetry, weakness, sensory loss, limp, muscle atrophy
purpose for NCS?
where are the waveforms generated from?
determine if theres a pathology of nerve or nerves, if so what level the pathology originates
studies generated in peripheral nervous system
whats a way to localize lesion
comparison of conduction between two segments of same nerve
what are good criterias for ordering or performing EDX
is it necessary?
will it help determine dx, tx, or prognosis?
is there a test that is less intrusive or more cost effective with the same info?
