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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4612_Библиотеки_им_академика_М_И_Перельмана
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Audiology Review: Preparing for the Praxis and Comprehensive Examinations
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322
TABLE 7–3. continued
TEST PURPOSE TECHNIQUE INTERPRETATION
Gait Speed Measure functional
mobility
Timed
Up-and-Go
Measure functional
mobility
(TUG)
Dynamic Gait
Index (DGI)
Measure of balance in
dynamic conditions
Patient walks at comfortable
and fast speeds for 3–10
meters.
Patient transitions from
seated to standing, walks a
3-meter line, turns around,
and sits down.
Patient completes a series
of balance tasks: (1) gait
on level surface, (2) change
in gait speed, (3) gait with
horizontal head turns,
(4)gait with vertical head
turns, (5) gait and pivot
turn, (6) step over obstacle,
(7) step around obstacle,
and (8) steps. The examiner
scores the patient’s ability
using a rubric.
Gait speed = distance / time
Normal values vary by
age, gender, use of assistive
device, and walking speed.
Normal:
≤13.5 seconds
Abnormal: >13.5 seconds
Normal:
≥22/24
Abnormal: <19/24
FIGURE 7–4. Bitemporal electrode montage and the connections to a two-channel
differential amplifier (i.e., two channels permit the recording of horizontal and
vertical eye deviations). Source: From Balance Function Assessment and Manage-
ment, Third Edition (pp. 1–717) by Jacobson, G. P., Shepard, N. T., Barin, K., Burkard,
R. F., Janky, K., & McCaslin, D. L. Copyright © 2021 Plural Publishing, Inc. All rights
reserved.
CHAPTER 7 Vestibular Assessment and Differential Diagnosis
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323
VNG
VNG recording uses pupil localizing technology to calculate the pupil’s position and gaze angle. Most
systems are fit with infrared diodes, reflexive glass mirrors, and small cameras.
n
The remaining discussion will use VNG as the default terminology. VNG testing includes
three major components (Table 7–4): oculomotor assessment, positional/positioning
assessment, and caloric assessment.
Gaze Testing
Gaze testing evaluates the patient’s ability to maintain gaze on a target in primary gaze (gaze center) and
in eccentric positions (right, left, up, down) in both vision/fixation and vision-denied conditions (i.e.,
10 conditions total). Abnormalities in gaze testing can occur from peripheral or central vestibular system
disorders. Look for nystagmus in primary and eccentric positions for vision and vision-denied conditions.
If nystagmus is observed, document the velocity, direction, and in which condition(s) it occurs.
Peripheral vestibular nystagmus should be horizontal or a combination of horizontal and torsional
should follow Alexander’s law. The following criteria are used to identify significant nystagmus:
n
Nystagmus present in any gaze position with velocity >5°/second
n
Nystagmus present in four or more conditions with velocity <6°/second
n
Nystagmus present sporadically in all gaze positions with velocity <6°/second
n
Direction-changing nystagmus noted within any gaze position
— it
TABLE 7–4. Key Components of Videonystagmography (VNG) Testing
COMPONENT SUBTEST FUNCTION
Oculomotor
Assessment
Positional/Positioning
Assessment
Caloric Assessment Assess peripheral VOR performance; gold
Note. BPPV: benign paroxysmal positional vertigo; VOR: vestibulo-ocular reflex.
Gaze with/without fixation Hold an image stable when the head is still
Saccades Quickly move the eyes to fixate on an object
of interest
Smooth pursuit Hold/track a moving object with the eyes
Optokinetic nystagmus (OKN) Maintain clear vision when the head or
target is in constant motion
Static positional recording in four
to six conditions: supine, head
right, head left, lateral right, lateral
left, caloric test position
Dix-Hallpike test
Lateral head roll test
Evaluate the effects of head orientation and
neck position on spontaneous nystagmus
Evaluate for BPPV
standard for identifying unilateral peripheral
weakness
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324
KNOWLEDGE CHECKPOINT: ALEXANDER’S LAW
Alexander’s law is associated with gaze-evoked nystagmus that occurs after an acute unilateral
vestibular loss. It was originally described to explain how the vestibular system, specifically the
VOR, responds to the injury. Alexander’s law includes three components:
1. Spontaneous nystagmus after peripheral vestibular insult has the fast phase directed toward
the healthy ear.
2. Spontaneous nystagmus (a) is greatest when gaze is directed toward the fast phase, (b) is
attenuated in center gaze, and (c) may be absent when directed toward the slow phase.
3. Spontaneous nystagmus is reduced with fixation and enhanced with vision-denied.
Spontaneous nystagmus is defined by the number of gaze positions. For example, if nystagmus is
only observed in gaze left, it is considered first-degree gaze-evoked nystagmus. Nystagmus present
in gaze left and center gaze is described as second-degree nystagmus, and third-degree gaze-evoked
nystagmus occurs with nystagmus in all three positions (Figure 7–5). Importantly, peripheral
vestibular nystagmus does not change direction or present with up-beating or down-beating nystagmus
— these presentations relate to central vestibular pathology.
FIGURE 7–5. Gaze evoked nystagmus is defined by the presence of nystagmus in one, two, or three
gaze positions. Peripheral vestibular nystagmus follows Alexander’s law.
Saccades
Saccades are conjugate eye movements that reposition the fovea on the target of interest. Saccades
are the fastest type of eye movements and can be evaluated using numerous protocols. Most clinical
protocols use a random saccade paradigm, meaning that the saccade location, intrasaccadic interval,
and fixation duration are random. Saccade abnormalities are not related to peripheral vestibular system
performance. Random saccade performance uses the frontal eye fields, brainstem, midbrain, superior
colliculus, cerebellum, frontal lobe, posterior parietal cortex, basal ganglia, and thalamus. It is important
to record each eye individually to identify disconjugate (i.e., eyes not moving together) eye movements.
There are three primary parameters for saccade analysis (Figure 7–6; Table 7–5).
CHAPTER 7 Vestibular Assessment and Differential Diagnosis
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FIGURE 7–6. Saccade parameters for analysis include latency, accuracy, and velocity.
325
TABLE 7–5. Summary of Saccadic Eye Movement Abnormalities
PARAMETER ABNORMALITY
Velocity Reduced velocity, both eyes
Fatigue, medications
•
• Abnormal performance of reticular formation, MLF, cerebral
hemispheres, superior colliculus, cerebellum
Reduced velocity, one eye or restricted direction
• Abnormal performance of reticular formation, MLF; question INO
Enhanced velocity
•
Calibration error
• Restrictive syndromes, late myasthenia gravis
Accuracy Hypometria
Fatigue, medications
•
• Bidirectional: cerebellar dorsal vermis
• Unidirectional: ipsilateral cerebellum/brainstem
Hypermetria
• Cerebellum
Latency Both eyes, all directions
Note. MLF: medial longitudinal fasciculus; INO: intranuclear ophthalmoplegia.
• Fatigue, medications
• Superior colliculus, reticular formation
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326
n
Accuracy: how far is the eye position from the actual target
Measured in percent (%)
Hypometria/undershooting: eyes are significantly short of reaching the target
Hypermetria/overshooting: eyes are significantly over the target
n
Latency: time between initiation of target movement to the initiation of eye movement
Typically between 150 and 200 ms
n
Velocity: how fast the eyes move to the target once movement begins
Measured as peak velocity
Ranges from 300° to 700°/second
The farther the target from the current eye position, the higher the expected peak velocity.
Smooth Pursuit
Smooth pursuit allows the eyes to hold a slow-moving target of interest on the fovea. This eye
movement performs most optimally below 70°/second. The underlying neural pathways include the
pons, cerebellum, VN, and pontine reticular formation. It is critical to use age-specific normative data
to interpret smooth pursuit, especially for advancing age. Smooth pursuit is the most sensitive oculomotor subtest for cerebellar dysfunction and should correlate with other metrics of cerebellar function.
Figure 7–7 provides an example of abnormal smooth pursuit. Note the stair step or saccadic quality to
this tracing. Gain for all test stimuli was significantly reduced. Additional oculomotor performance was
abnormal with down-beating nystagmus noted throughout gaze testing, prolonged saccade latencies,
FIGURE 7–7. Smooth pursuit tracing at 0.2 Hz for a 65-year-old male presenting with onset
of unsteadiness over the last 6 months.
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and reduced optokinetic nystagmus. VOR performance as measured by caloric testing and sinusoidal
harmonic acceleration (SHA) was within normal limits; however, the patient demonstrated inability to
appropriately fixate (VOR-Fixation). This patient presentation is highly suspicious for central vestibular system pathology, specifically involving the cerebellum. Smooth pursuit is evaluated with the
following parameters:
n
Velocity gain = peak eye velocity/peak target velocity
Abnormal performance may be associated with increased saccadic movements and
could relate to (a) acute peripheral vestibulopathy with active spontaneous nystagmus or
(b)brainstem or cerebellar lesion.
Asymmetrically reduced performance may relate to involvement of the ipsilateral
cerebellum, brainstem, or parieto-occipital region.
n
Asymmetry: difference in velocity gain between rightward and leftward eye movements;
results given in percent (%)
n
Phase angle: how much the eyes are ahead of (leading) or behind (lagging) the target
n
Saccadic component: how much the patient uses saccades instead of smooth pursuit to follow
the target; results given in percent (%)
Optokinetic Nystagmus (OKN)
OKN testing is a measure of both smooth pursuit and another neural substrate that encodes moving
visual stimuli. As the visual stimuli move, the eyes should generate a nystagmus response comparable
to the velocity of the visual field. To truly measure this response, the visual stimuli must fill >90%
of the visual field and generally requires testing within an enclosure. OKN paradigms that use a
lightbar are not true OKN measures and can only be used to describe the smooth pursuit pathway.
OKN is the least sensitive oculomotor measure for central pathology. OKN is evaluated with the
following parameter:
n
Velocity gain = peak eye velocity/peak target velocity
n
OKN is generally reported as normal or abnormal; velocity gain should be >0.5 of the target
velocity for an appropriate response.
Positional Assessment
The positional assessment evaluates the presence of nystagmus in various head positions in relation to
gravity. Nystagmus may occur with or without dizziness when the patient is in these static positions.
Observed nystagmus may relate to impaired SCC(s), otolith organ(s), or central vestibular pathways.
By changing the head position, the orientation of the inner ear toward gravity changes, thus altering
the underlying neural firing that represents the specific head position. In general, positional nystagmus
should relate to asymmetrical peripheral or central vestibular system performance. Positional nystagmus is also commonly observed with alcohol consumption and some medication use. Most clinicians
evaluate the following positions:
n
Supine, head center
n
Supine, head right
n
Supine, head left
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n
Caloric test position (30° recumbent), head center
n
Optional positions may be included if nystagmus is observed in the above conditions or if a
specific condition is known to provoke dizziness.
Lateral, body right
Lateral, body left
Head hanging, center
Head hanging, right
Head hanging, left
The following criteria are used to determine if any visualized nystagmus is significant. Note that
these criteria are the same as those used for evaluating spontaneous nystagmus in gaze testing.
n
Nystagmus present in any position with velocity >5°/second
n
Nystagmus present in four or more positions with velocity <6°/second
n
Nystagmus present sporadically in all positions with velocity <6°/second
n
Direction-changing nystagmus noted within any position
If the nystagmus noted in positional testing is the same velocity and direction as that observed in
gaze testing, it is not a significant/novel finding (i.e., it is consistent with the underlying spontaneous
nystagmus).
n
Nystagmus will be either direction-fixed (only one direction of nystagmus noted in all
positions) or will change direction depending on head position. In this case, nystagmus is
described as geotropic (toward the ground) or ageotropic (away from the ground). This is
NOT direction-changing nystagmus. Geotropic/ageotropic nystagmus changes direction with
different head positions but is consistent within the same head position. This presentation
relates to the altered interactions between the otolith organs and SCCs in acute peripheral
vestibular loss; however, central vestibular pathology may also present with this finding,
and the site of lesion is determined by evaluating the patient’s entire presentation and case
history. In either case, the patient is generally asymptomatic. If the patient becomes dizzy with
these changes in head position, consider benign paroxysmal positional vertigo (BPPV) as a
possible diagnosis.
Positioning Assessment/Dix-Hallpike Test
Positionally provoked dizziness is the most common type of peripheral vestibular system pathology. It
can be easily tested for in isolation or as part of the VNG protocol. See sections below on BPPV for
testing, clinical presentation, and management.
Caloric Assessment
The caloric assessment is the most common measure of peripheral vestibular system integrity. Abnormal
findings are associated with a peripheral lesion involving the horizontal SCC and/or superior branch of
the vestibular nerve on the side with the weaker response. This test can be completed with water or air
as a stimulus, but specific temperatures and irrigation characteristics must be used. Water irrigations are
considered more reliable than air irrigations because there is less room for technical/user error. Further,
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water provides a more robust stimulus and therefore requires a shorter irrigation time. Water irrigations
cannot be used in cases of eardrum perforations due to increased risk of infection. Air irrigations should
be used in these situations.
The nystagmus response to caloric stimulation follows an expected pattern due to the ampullopetal (excitatory) flow induced by warm irrigations and ampullofugal (inhibitory) flow induced by cool
irrigations. To remember the expected response, think “COWS”—
cool opposite, warm same.
During the irrigation, the patient may experience a sense of dizziness or vertigo. This typically
begins about halfway through the irrigation and peaks by 30 seconds after the irrigation is complete
(i.e., 60 seconds for water, 90 seconds for air). At this point, it is important to provide a fixation target
to document the patient’s ability to suppress the caloric response (fixation suppression/fixation index).
Q & A
Question: What specific irrigation temperatures, durations, and volumes are
needed for water and air caloric stimuli?
Answer: The irrigation parameters recommended by the British Society of
Audiology (BSA, 2010) are provided in Table 7–6.
Question: What nystagmus response do you expect for each ear following each
irrigation temperature?
Answer: You should expect the following caloric responses based on the test ear
and irrigation temperature (Table 7–7).
TABLE 7–6. Caloric Stimulus Parameters
STIMULUS TEMPERATURE DURATION VOLUME
Water Warm: 44 degrees Celsius
30 degrees Celsius
Cool:
Air Warm:
Cool:
TABLE 7–7. Expected Caloric Responses by Ear
and Temperature
TEMPERATURE EAR RESULT
Warm Right
50 degrees Celsius
24 degrees Celsius
Left
30 seconds 250 ± 10 ml
60 seconds 8 ± 0.5 liters
Right-beating nystagmus
Left-beating nystagmus
Cool Right
Left
Left-beating nystagmus
Right-beating nystagmus
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The fixation target should be visible for approximately 10 seconds before returning to the vision-denied
condition to document the increase in nystagmus velocity (Figure 7–8). This ensures that any decline
in nystagmus velocity is related to the patient’s fixation ability and not simply due to the natural decline
in velocity. Nystagmus should be reduced by at least 60% with fixation.
To interpret the caloric response, identify the peak nystagmus velocity for each irrigation and
evaluate for the following:
n
Unilateral weakness
Also known as canal paresis (CP)
Calculate the difference between ears using Jongkees’s formula:
[(right warm + right cool) − (left warm + left cool)]
CP =
(right warm + right cool + left warm + left cool)
Abnormal CP >25%
Almost always due to peripheral vestibulopathy
Rule out technical error: poor irrigation, cerumen blocking the ear canal, surgical ear, ear
drum perforation
n
Bilateral weakness
Also known as bilateral areflexia or hypofunction
Calculate the total eye speed (TES) for each ear:
FIGURE 7–8. Analysis of caloric nystagmus in three time intervals: A. Around 10 to 15 seconds after the
onset of the irrigation to determine the baseline shift. B. Around 60 to 90 seconds after the onset of the
irrigation to determine the peak caloric response. C. Around 5 seconds before and 10 seconds after visual
fixation (identified by gray timeline) to determine fixation suppression of caloric nystagmus. Source: From
Balance Function Assessment and Management, Third Edition (pp. 1–717) by Jacobson, G. P., Shepard, N. T.,
Barin, K., Burkard, R. F., Janky, K., & McCaslin, D. L. Copyright © 2021 Plural Publishing, Inc. All rights reserved.
CHAPTER 7 Vestibular Assessment and Differential Diagnosis
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●
Right TES = right warm + right cool
●
Left TES = left warm + left cool
Bilateral weakness is defined when each ear’s TES is <12°/second.
May occur due to bilateral peripheral vestibulopathy (e.g., ototoxicity) or central
vestibulopathy (e.g., cerebellar degeneration)
Rule out technical error: poor irrigation, cerumen blocking the ear canal, surgical ear, use
of vestibular suppressant medications (e.g., meclizine)
Confirm with additional VOR metrics such as rotational chair, video head impulse testing
(vHIT), DVAT, mCTSIB/balance testing, and/or ice water caloric irrigations
n
Hyperactive responses
Calculate the TES for each ear as above
Caloric hyperfunction is defined when each ear’s TES is >140°/second
Rule out technical error: perforated eardrum, altered mastoid
May be associated with loss of VOR inhibition in the vestibular nuclei or cerebellum (Baloh
et al., 1975)
n
Directional preponderance
331
Comparison of right-beating versus left-beating nystagmus
Calculate TES for each nystagmus direction
●
Right-beating TES: right warm + left cool
●
Left-beating TES: left warm + right cool
Calculate directional preponderance (DP)
[(right warm + left cool) − (left warm + right cool)]
DP =
(right warm + right cool + left warm + left cool)
Abnormal DP >30%
Most commonly abnormal in patients with underlying spontaneous nystagmus. If present
in a case with no spontaneous nystagmus, consider technical error or nonlocalizing
finding.
n
Fixation index
Also known as fixation suppression
Comparison of peak nystagmus velocity to nystagmus velocity during fixation
Abnormal fixation index <60%
Abnormal fixation index suggests cerebellar involvement. Confirm with other measures of
cerebellar performance (e.g., smooth pursuit)
n
Monothermal irrigations
Some laboratories use monothermal irrigations to screen patients. Either warm or cool
irrigations are used.
Calculate CP using a modified Jongkees’s formula:
CP =
right − left
right + left
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