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AUD spring 2020 Electrophys II > Week 15: electroneuronography > Flashcards

Week 15: electroneuronography Flashcards

1
Q

what portion of the VII nerve is motor and what is sensory

A

2/3 motor and 1/3 sensory so mainly a motor nerve

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2
Q

what muscles does the facial nerve innervate

A

facial muscles, stapedius, stylohyoid, and digastrics muscles

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3
Q

what are the two main branches of the facial muscle?

A

temporal and cervical

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4
Q

what are the 5 divisions of the facial muscle

A 
temporal
zygomatic
buccal
mandibular
cervical
*note that the buccal branch allows communication between the zygomatic and mandibular branches
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5
Q

what do we look for visually to cue for a facial nerve lesions

A
  • forehead= corrugation
  • eyes= orbicularis occuli
  • nasolabial fold
  • mouth= purse lips
  • cheeks= inflate cheeks
  • symmetry of both sides
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6
Q

what are the 4 ways we can look for facial nerve functioning

A
  • clinically with facial grading system
  • imaging:
  • –MRI with IV gadolinium contrast to see VII nerve tumor in the CPA and temporal bone, or parotid gland tumors
  • –CT scan for cholesteatomas and temporal bone trauma
  • electrophysiologically
  • –stimulation and recording techniques
  • –interpretation and reporting guidelines
  • histologically
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7
Q

house-brackman system for facial nerve paralysis grading

A
  • 1=none=normal function in all areas
  • 2=mild= slight weakness on close inspection, synkinesis
  • 3= moderate= obvious but not disfiguring asymmetry
  • 4=moderately severe= obvious, disfiguring asymmetry; normal appearance at rest
  • 5= severe= barely perceptible motion; asymmetry at rest
  • 6=total= no perceptible motion
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8
Q

histological sunderland classifications of 7th nerve damage

A

*grade 1= neuropraxia= conduction block and is just a bit of compression on the axon, no real injury
*grade 2= axonotmesis= axonal discontinuity/injury to the axon
*grade 3= neurotemisis type 2= the tube (endoneurem) and axon are disrupted neurotemisis which has grades
*grade 4= neurotemeisis type 3 which is where the epineurium is also affected
grade 5= neurotemisis type 4 which is where is entire nerve is injured and is broken
—wallerian generation degeneration is anything more than grade 1

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9
Q

what electrophysical tests are used to see VII nerve injury

A
  • nerve excitability test (NET)
  • maximal stimulation test (MST)
  • electromyography (EMG)
  • electroneurography (ENoG)
  • determining prognosis
  • –rarely in differential diagnosis
  • classifying nonsurgical vs surgical management
  • IOM of VII nerve function (usually with EMG)
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10
Q

NET (nerve excitability test)

A

*useful only during the first 2-3 weeks of complete paralysis, before complete degeneration has occurred to determine whether a pure conduction block exists or whether degeneration is ocurring
*the stimulating electrode is placed on the skin over the stylomastoid foramen or over one of the peripheral branches of the nerve
*beginning with the healthy side, electrical pulses steadily increasing current levels until a facial twitch is noted
*the lowest current eliciting a visable twitch is the threshold of excitation
*next the process is repeated on the paralyzed side
*a difference of 3.5 milliamps or more is a sign of severe degeneration and an indicator for surgical
decompression
—simple conduction block would have no difference between the sides

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11
Q

MST (maximal stimulation test)

A
  • stimulating all intact axons
  • nerve-stimulating equipment are the same as the NET. *Maximal stimuli or supramaximal stimuli are used
  • –start at 5mA and increase to the level of the patient’s tolerance
  • on the unaffected side, the stimulus current intensity is increase until the maximum stimulation level
  • this level is then used to stimulate the affected side
  • –the degree of facial contraction is subjectively assessed as either equal, mildly decreased, markedly decreased, or without response compared to that of the normal side (0%, 25%, 50%, 75%, 100%)
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12
Q

the beginning of ENoG

A

*developed by Esslen and Fisch in 1979

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13
Q

what does ENoG show

A

the distal VII nerve function
*we record the facial nerve function from the peripheral (aka from the muscles of the face) and we record from each side and compare the latency and amplitude of the N1, P1, N2 wave

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14
Q

overview of ENoG testing

A
  • used in Bell’s palsy, trauma, otitis media
  • –not useful in Ramsay Hunt because the virus causing this gives severe nerve problems and multiple sites of facial nerve lesions
  • VII nerve is stimulated transcutaneously (as in NET) or using a bipolar stimulating electrode
  • comparing responses from both sides to maximal electrical stimulation (as in MST)
  • –compound muscle action potential (CMAP)
  • normally: the average difference in response amplitude between the two sides is only 3%
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15
Q

why is Enog measured

A
  • to see the extent of VII nerve degeneration (wallerian degeneration=WD=% of neural fibers that are no longer responding
  • comparing the response amplitude (and latency) of both sides
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16
Q

how would a tumor affect your ENoG response

A

increase latency and decrease amplitude

—decrease amplitude= increasing tumor size

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17
Q

how to assess abnormal amplitude responses

A

*if the response on the paralyzed side is 10% of that on the normal side then 90% of the fibers are severely degenerated and so on

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18
Q

when do you do ENoG (timing)

A
  • initial/baseline ENoG most useful between 4-21 days post insult
  • –not before 72 hrs post-insult because WD takes 3 days to occur
  • –not after 3 wks; false positive from deblocking
  • serial ENoG, every 3-5 days
  • –document improvement or further degereration
  • response is affected by neuroblockers–which cause chemical paralysis of VII muscles
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19
Q

what do you have to do to your evoked response system to do ENoG

A

*add an additional unit that is an electric generating device to deliver electric stimulus and the software

20
Q

electrode placing for ENoG

A

place on the face to monitor the muscle activity of various portions of the face

  • –use the same surface electrodes
  • noninverting (+) at the angle of the mouth (ipsi)
  • inverting (-) :nasolabial fold (ipsi)
  • ground :forehead (fz)
  • again stimulating distally at the stylomastoid foramen with a bipolar stimulus electrode
  • –which means it has an anode and a cathode
21
Q

recording parameters of ENoG

A
  • analysis time: 12-20 ms
  • filter settings: 3-300 Hz
  • notch filter: no
  • amplification: 5000 or less
  • impedance: <5 kohms
  • sweeps: 1-20
22
Q

stimulus parameters for ENoG

A
  • transducer: pair of electrodes
  • site: stylomastoid foramen (main trunk of the nerve)
  • orientation: anode + is the anterior and cathode - is the posterior
  • –red is front and black is back
  • type: constant current pulse
  • mode: continuous
  • duration: 0.2 ms (200 microseconds)
  • laterality: unilateral (uninvolved side first)
  • intensity: >10 mA
23
Q

ENoG waveform analysis by response amplitude

A
  • intensity >10mA to produce supra-maximal P1 response
  • biphasic waveform w/in the first 5-7 ms after electrical stimulation
  • –N1, P1, N2 deflection
  • different methods of calculation amplitude leads to high variability in the amplitude of p1
  • limitation: abnormal ENoG in individuals with normal clinical VII function
  • **note a response earlier than 4 ms is not true response, you pros stimulated the massiter muscle
24
Q

ENoG waveform analysis

A
  • documentation of normal vs abnormal side is important:
  • –ask pt to smile to identify the stronger side of the face
  • –or use medical records
  • response analysis to determine abnormal asymmetry in amplitude (or latency) between both sides
  • if one side is 750 and the other is 40 mV then do the calculation to know the % of wallerian degeneration
  • ——-40/750=5% or 95% degeneration
  • –this test is not to diagnose, but is to determine the amount of asymmetry to see the amount of wallerian degeneration
25
Q

at what degree of asymmetry means surgical intervention is helpful

A

*response of <10% (90% wallerian degeneration) may suggest a surgical intervention (no spontaneous recovery)

26
Q

how to interpret ENoG results

A
  • significant degeneration requiring surgical intervention
  • –response <10% (or >90% WD) of the normal side
  • spontaneous recorvery–wait and see
  • –any response >10% (or less than 90% wallerian degeneration
  • note if you increase the intenstiy and dont get a bigger response, this is a problem and could be due to demyelination
  • –note that you want to use the same intensity between ears
27
Q

ENoG waveform analysis of latency of the response

A
  • VII Tumors:
  • –delayed latency and decreased amplitude
  • –decreased amplitude shows increasing tumor size
  • delayed latency and normal amplitude
  • –distal nerve demyelination
  • –reduction in the synchrony of neural response
28
Q

how to monitor with ENoG

A

*serial testing every 3-5 days until normal, stable, or improving ENoG indicates good prognosis

29
Q

test instructions for ENoG

A
  • patients are anxious and apprehensive about the test procedure–they are in pain
  • –take time to explain the procedure
  • –avoid terms that will cause alarm or concern
  • procedure leads to some discomfort
  • –patient will tolerate some discomfort to reach the diagnosis
  • –patient can stop the test if it becomes too uncomfortable
  • —–start at low presentation level and build up if necessary
30
Q

troubleshooting no ENoG response, bilaterally

A
  • chemical paralysis– in the OR or ICU
  • –reverse neuromuscular blocking agent medically (physician can give the pt an anti-inflammatory and then have them come back)
  • improper electrode placement
  • –verify correct electrode placement
31
Q

troubleshooting poor ENoG response, bilaterally

A
  • edema at stimulation side
  • –relief pain and anti-inflammatory
  • inadequate stimulus electrode pressure (ie) tenderness.pain, obese patient)
  • –apply more pressure—relief pain
  • –needle electrode
  • bilat dysfunction or injury
  • –compare patient ENoG amplitudes to normal data
32
Q

troubleshooting ENoG when there is a poor response unilaterally

A
  • inappropriate stimulus site
  • –relocate stimulating electrodes
  • –increase stimulus intensity to supra-max level
33
Q

troubleshooting ENoG when there is an early response

A
  • <6ms, but 4 ms is what she said was the cutoff for early earlier
  • masseter muscle response
  • –move stimulating electrode posteriorly
  • –if stimulating the masseter muscle, the you need to move the stimulating electrode back towards the back of the head direction
34
Q

troubleshooting ENoG when you have excessive artifact rejection (to the point where you cannot average)

A
  • stimulus artifact
  • –increase distance between the stimulating and recording electrodes
  • –avoid crossing of stimulus and recording electrode wires
  • –decrease amplification (gain) to 3000
35
Q

what is the main indication that you want to do IOM of the VII nerve

A

if there is at least some preoperative neural function, not total degeneration
—you wouldnt want to monitor if there is a total degeneration or mostly degeneration of the nerve

36
Q

the 5 IOM objectives (for the 7th nerve)

A
  • distinguishing the VII nerve from other cranial nerves, tissue, etc
  • facilitation of tumor excision by verifying that regions of the tumor are remote from the VII nerve
  • early recognition of surgical trauma to the VII nerve
  • confirmation of nerve stimulation following tumor removal–post-op prognosis
  • identification of site and degree of neural degeneration in nerve exploration cases for suspected VII tumors or decompression for acute VII palsy
37
Q

what are 5 otologic surgeries you would want to do VII nerve monitoring for

A
  • IAC and CPA tumors
  • vestibular neurectomy
  • cochlear implantation
  • cholesteatoma
  • congenital aural atresia
38
Q

what are 4 non-otological surgeries you would want to do VII nerve monitoring for

A
  • VII nerve surgeries
  • –decompressing, mobilizing nerve
  • parotid gland tumors
  • posterior fossa tumors compressing VII nerve
  • hemifacial spasm (HFS)
39
Q

what is HFS

A
  • hemifacial spasm
  • in hemifacial spasm, the nerve has an offending loop of blood vessel, compressing the facial nerve at the root entry zone
  • –observe the VII nerve root as tit leaves the brainstem
  • the vascular loop could also be around the cochlear nerve causing tinnitus and SNHL
40
Q

why do we monitor the VII nerve (3 reasons)

A
  • cosmetic consideration
  • loss of VII nerve function is costly
  • functional implications to the eye
  • –lack of tears
  • –improper closure
  • –injury to the cornea
  • study actually showed lowest quality and higher cost associated with decision NOT to provide facial nerve monitoring because the surgery to repair the facial nerve is very costly
41
Q

what are the two electrodes for the IOM VII nerve monitoring

A
  • monopolar stimulators
  • –for tumor mapping but some current spread away from the tip of the stimulating probe
  • –look like a needle electrode and it is placed on the nerve, the current goes through the electrode and you record from the electrodes on the muscles of the face
  • bipolar stimulators
  • –to separate the facial nerve from adjacent neural structures
  • –reduces false-positive response form the surrounding neural tissue
  • –concenteric=bipolar and it has two tips, where you can put the facial nerve in between the two tips which would help separate the facial nerve from other neural structures (reduces splatter of the stimulating current)
42
Q

what happens with VII stimulation with IOM

A
  • the facial muscles will fire off
  • –will give visual waveforms
  • –and audible sounds
  • **use needle electrodes and we are looking at the peripheral effect of the stimulation of the facial nerve
43
Q

how does the VII nerve elicit sound acitvity

A
  • intentionally electrical stimulation
  • –present electrical current and record direct VII nerve stimulation
  • –this electrical stimulation will cause precisely timed locks
  • direct surgical/mechanical manipulation
  • –nerve it touched, compressed, or stretched by fluid irrigation causing bursts, electrocautery, or laser devices
  • —–direct surgical manipulation will cause bursts at several clicks at the time of manipulation
  • —–traction, pressure, or calorics will cause training which would be repetitive asynchronous clicks like pop corn
  • **can hear audible responses when the surgeon is purposely stimulating the nerve so you hear pulses that are precisely time locked with the stimulus; this is a good sign the facial nerve is functioning
44
Q

what is the deal with bursts of EMG activity with VII nerve monitoring

A
  • fluid irrigation, manipulation of the nerve

* suggests functional integrity of the nerve distal to the point of stimulation

45
Q

what is the deal with train of EMG activity with VII nerve monitoring

A
  • dissector device, electrocautery, drilling, nerve ischemia, stretching of the nerve
  • suggesting some neural trauma and post op decrease in VII motor function
  • -this means you must inform the surgeon
46
Q

how can more audiologists be involved in IOM

A
  • education and training

* specialty certification

AUD spring 2020 Electrophys II (13 decks)

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