NCS Flashcards
What must be positive on EMG to diagnose something as a “generalized process”
positive findings in at least 3 extremities.
depolarization at the cathode occurs in ____ direction.
It is slowed _____ thanks to the anode
both
proximally because of hyperpolarization over the anode
A ____ study is when an impulse travels away from the stimulator in the opposite direction that it does physiologically.
antidromic
CMAP stands for ___ and is found in ____ study
compound muscle action potential - pure motor study
SNAP stands for ___- and is found in ____ study
Sensory nerve action potential; pure sensory (stimulate over entire peripheral nerve and pickup discally)
CNAP stands for ______ and is found in ____ study
Compound nerve action potential - stimulate over a mixed nerve and pickup over the nerve proximally. Pick up sensory and motor fibers.
assesses the functional status in health and responses to various disease processes. NCS allow to localize focal lesions or detect generalized disease process.
What are the disadvantages for needle electrode stimulation (4)
- if voltage is too high, can burn the patient. Must turn the duration(sweep) down
- Can injure nerve if stuck through the nerve
- if trying to stimulate erbs point or spinal accessory nerve, can give pt a pneumothorax
- increase infection risk
what are two advantages of stimulating with needle electrode?
- more precise localization of depolarization
- can use less current or volts therefore less pain
Advantage of surface stimulation 2
- less chance of infection, but not zero
- must use supramaximal stimulation to compare one study to the next.
Recording electrodes:
______: sumation of all electrodes in the area
______: cannot compare amplitude to amplitude but can compare latencies
surface
electrode (needle)
If pathology is proximal to the dorsal root ganglion, ____ will be normal
SNAP
In a motor NCS, active is placed _____ and reference is placed ______
belly of muscle (mid-portion)
something inert.
What is the problem if you first see a positive deflection on motor NCS (CMAP)
surface electrode is not over midpoint of muscle.
Motor latency is measured at ______ latency
onset
sensory latency is measured at _____
peak latency.
fastest axons will be seen at ______
onset latency
there is 13ms difference between fastest axon and others. This becomes more if pathological case. If axon is affected onset latency moves to the R.
Area under the negative spike =
of axons
All of the following occur prior to onset latency: (3)
The time required to achieve neuromuscular transmission and muscle action potential induction with subsequent CMAP appearance on the CRT is about 1ms determined by these things.
- latency of activation = 0.1msec
- neuroconduction
- NMJ transmission 1.0 msec
Most sensitive marker in demyelination process is _____
increase in negative spike duration
amplitude is measured :
peak to peak
Nerve conduction velocity:
Sensory:
Motor:
Sensory: distance/(OL - 0.1msec)
Motor: Motor study - NCV = distance/time.
Have to stimulate two points, distally and proximally.
Normal onset latency is _____ for upper extremity and ____ in lower
45m/sec, 40m/sec
On a motor study, the more proximal you go, you will get ______
physiologic temporal dispersion - every axon in the nerve doesn’t run at the same conduction velocity. If you’re more proximal, the potential spreads out more and they cancel each other out. The more proximal you go, you’ll lose amplitude. If the amplitude drops 50% that’s considered to be normal. Anything over 50% is abnormal
in physiologic temporal dispersion, amplitude ____ and duration _____
decreases, increases
______ occurs with turning up intensity and supramaximal stimulation does not occur
pseudofacilitation - if you do repetitive stimulation and the amplitude of the waveform gets bigger. There is better synchronizing of the motor units and it gets better with repetitive stimulation.
If you reach supramaximal stimulation and you get different morphology, its probably a ____ problem
NMJ
Which study is a pure sensory study
sural
What types of sensory NCS are there? (3)
- pure sensory - sural
- Pure sensory to mixed nerve
- Stim mixed nerve pick up over pure sensory.
in SNAP, orthodromic and antidromic studies are equal with respec to ____ and ____ but not in _____
onset and peak latency, amplitude.
Physiologic temporal dispersion is more pronounced in sensory nerves than motor nerves because: (2)
- SNAP negative spike duration is shorter than that for CMAP, resulting in less tolerance to asynchronous summation resulting in phase cancellation.
- the difference between the fastest fibers and the slowest fibers is mroe dramatic in sensory fibers. (more variation). The dispersion between the fastest and the slowest sensory nerves is twice that for motor nerves. In sensory nerves its 25m/sec. In motor its 13m/sec.
in SNAP, active and reference electrodes must be ____ cm apart. If less than that, what happens to amplitude?
4cm
decreases
(founded by 50m/s = (X/0.8ms)
Physiologic effects of NCS
Height:
Age:
taller = slower conduction(secondary to tapering of the axons. The larger the nerve diameter, the faster the NCV. Taller, tapers over a longer length, small diameter later
newborn has 1/2 the speed of an adult.
Reaches adult values at 3-5 years of age.
After age 50, there is progressive decline in conduction velocity of the fastest motor nerve fibers approximating 1-2m/sec per decade.
After age ____, there is progressive decline in conduction velocity of the fastest motor nerve fibers approximating _____ per decade.
50
1-2m/sec per decade
at 40-60yoa, CV is ____ that of an 18yo
at 70-80yoa, CV is ____ that of an 18 yo
1/2
1/3
Increasing the lower frequency filters:
____ amplitude
____ peak latency
____ negative spike duration
____ onset latency
(left shift)
decreased amplitude
Decreased peak latency
decreased duration of neg spike
no change in onset latency
Increasing the high frequency filter
_____ amplitude
_____ peak latency
_____ onset latency
_____ negative spike duration
R shift
decreased
increased
increased
increased
If motor action potential shows motor potential and SNAP, what three things should you do
- rotate anode
- remove lotion/sweat
- remove some gel
digital circumference affects:
amplitude
same with edema
If you decrease the temperature in NCS, what 6 things will occur?
- increased amplitude (b/c prolongation of sodium inactivation which causes longer depolarization)
- prolonged latency
- decreased conduction velocity
- increased negative spike duration
- increased area under the curve
- increased rise time.
for every degree below 33 degrees in the UE, you decrease the CV by ____
2.4m/sec
- can make up for temp by either warming the person up or adding 2.4m/sec to each degree until the temperature is 33 degrees to correct for your velocity.
The peak latency increases on a sensory study to ____ msec for each degree decrease in temp below 33 degrees
0.2msec
what is martin gruber anastomosis
where does it cross? (3 with percentages)
median to ulnar transfer of nerves in the forearm.
AIN (91%)
FDS 6%
main to ulnar 3%
nerves are actually ulnar to median in the plexus.
Martin gruber is what inheretence pattern?
____% are bilateral
autosomal dominance 7-34% incidence
68%
martin gruber goes to what muscles (3)
- FDI 95-100%
- hypothenar muscles 41-60%
- Abductor pollicis - 74%
martin gruber will look like what in a normal person
distal stim normal
prox (elbow) will have increased amplitudes instead of decreased like with normal phys dispersion
what will martin gruber look like in someone with CTS
prox will get a + deflection with higher amplitude because the ulnar axons arrive first, Will also get supraphysiologic conduction velocity.
What is riche cannieu hand?
Present in _____% of hands
When is this pertinent?
Connection of deep branch of ulnar nerve and recurrent branch of the median nerve in the hand. Causes an “all ulnar hand”.
77%
in complete laceration of median or ulnar nerve in forearm. If median nerve, will not loose thumb abduction and opposition if they have this anomaly.
What is an accessory peroneal nerve?
Present in _____% of patients
______% is bilateral
Inheritence?
a branch of the superficial peroneal nerve that procedes posterior to the lateral malleolus and innervates the lateral portion of the extensor digitorum brevis.
28%
57%
Autosomal dominant
Reference over EDB and stimulate the deep peroneal nerve at the fibular head which results in CMAP from teh EDB with a smaller magnitude than that evoked from the ankle. A larger amplitude proximally may lead one to consider the possibility of submaximal stimulation of the deep peroneal nerve at the ankle, or an accessory deep peroneal nerve.
F wave is ____ in and ____ out
motor
motor
found in every motor nerve
F waves originally described in ____.
Foot
F waves are the first thing to be positive in ____ and ____
GBS or AIDP
test peroneal and tibial & will be present bilaterally
______ is when stimulation is folllwed by initial depolarization in both directions, first directly to the muscle fiber producing the M response, and retrograde up tot he axon and to the neuron, where it is repropogated in a small percentage of neurons back down the axons to produce the delayed response
f wave
do 10 and take the fastest of the 10. Normals are based on limb length
in F waves, ______ msec of side to side variance is acceptable in upper extremities, ____msec in lower extremities, and ___ in foot muscles
2msec
3msec
4msec
What is chronodispersion?
variation in latency
F waves are _______. Goes into the spinal cord into the anterior horn cell and can take different routes through the interneuron pool and then comes back out the anterior horn cell
multisynaptic/polysynaptic
causes variability in waveform.
In F waves, can stimulate UE to ____ and lower extremity to _____
C7, T12 (where spinal cord ends)
where normals are obtained (based on height an limb length)
_____ is the ratio of F wave amplitude to that of the m wave to (no clinical utility of these measurements)
F persistence - of the 10 you did, how many had an F wave.
What is the F/M amplitude?
in an F wave, this is the F wave amplitude (microvolts) divided by the M wave amplitude (millivolts) measured peak to peak. Measure of a proportion of a motor neuron pool activated by the antidromic stimulation
H reflex is ___ in and ___ out
sensory in, motor out
hoffmans reflex
H reflex stimulates ____ fibers
large 1A myelinated fibers
H reflex is a ____ pathway
monosynaptic (no variation in wave form)
_____ is obtained by stimulation of the afferent sensory fibers (top) resulting in orthodromic conduction to the spinal cord. In the spinal cord, there is a synaptic stimulation of the alpha motor neuron, this results in evoked response in the muscle. A rudimentary M response is produced when a few motor axons are directly stimulated
H response
H reflex is found in all muscles in ____
newborns
as we age, which two muscles can H reflex be found in?
- Gastroc soleus (tibial nerve) - clinically significant and equal tot he achilles reflex. S1 radic will make it absent or prolonged (1.2msec)Can differentiate if its a sciatic nerve injury or a sacral plexus injury b/c theyr’e along the same route and could be the problem.
- flexor carpi radialis (median nerve) - used for C6 radiculopathy.
How do you do a H reflex for gastroc soleus
pick up over gastroc-soleus. Lay person down on stomach, get them to bend knees up, make a line across the popliteal fossa and from the midpoint of that line measure to the medial mall and take 1/2 the distance for the pickup point.
Reference over the achilles tendon.
Ground b/w tim and pickup
Stimulate in opposite direction, so the cathode is pointing north and stimulate proximally first.
Positive deflection first because your not directly over the motor point.
Stimulate submaximally so you get the sensory axons preferentially.
What number is the cutoff for abnormal in H reflex?
1.2msec with side to side comparison (has to do with 95% confidence interval)
_____ is a flare response of histamine reaction.
axon reflex
A present axon reflex indicates _____
pathology; diagnostic value is not certain but might indicate collateral sprouting at prox segment of the nerve.
If on axon reflex, the stimulation is increased, ____ occurs
blocking and axon reflex is lost.
A waves are ____ common than axon reflexes
more common
A waves are in a ____ configuration
constant - found in moderate and high intensities (recall axon reflex is lost if stimulation is increased)
what is the diagnostic value of A wave?
collateral sprouting
Is demyelinating or axonal pathologies more common in A waves?
UE or LE?
Demyelinating > axonal pathologies
LE > UE
All of the forearm muscles are innervated by the median nerve except for ____ and ____
FCU and medial two bellies of FDP
In the hand, all the intrinsic muscles are innervated by the ulnar nerve except (4)
- abductor pollicis brevis (APB)
- Opponens pollicis (OP)
- 1/2 of flexor pollicis brevis (FPB)
- 1st two lumbicals
IF you observe the following, what should you consider?
- initial positive CMAP deflection with proximal median nerve stimulation
- Significantly elevated median nerve NCV
- Larger proximal than distal CMAP on median nerve stimulation
- CMAP from ulnar innervated hand intrinsics with ulnar activation should be larger from the wrist when compared to the elbow
martin gruber anastomosis
What should you suspect if you encounter a larger peroneal nerve response from teh EDB with fibular head compared to ankle stimluation, one should first ensure proper activation of the peroneal nerve at the ankle
accessory deep peroneal nerve
Most sensitive test for median neuropathy is:
orthodromic mixed nerve study. Stimulate in teh palm over the median nerve between digits 2 and 3 and compare to digits 4 and 5 on the ulnar side. Delay of 0.2milliseconds consistent with slowing.
