Praxis Random Chp7 Part 1

What do the SCCs detect?

angular acceleration; encode rotational movements

What is the sensory epithelium in the SCCs? Where is it located?

crista ampullaris; located in ampulla

What is the cupula?

gelatinous structure extending across SCC to create fluid-tight seal

What does the cupula respond to?

Cupula acts like a sail and deflects when the head turns to trigger the underlying sensory epithelium

Cupula only responds to angular acceleration because it is the same specific gravity as the surrounding endolymph

What do the saccule and utricle encode?

Utricle - horizontal acceleration

Saccule - vertical acceleration

How to remember: when drawing a “U”, goes side to side; when drawing a “S” goes up and down

What is the sensory epithelium of the otolith organs?

otolithic membrane

What are the otoliths or otoconia? How do they encode horizontal and vertical accleration?

Calcium carbonate crystals embedded in the otolithic membrane

Otoconia increase specific weight of otolithic membrane, causes it to pull toward gravity or to lag during linear acceleration, triggers the underlying sensory hair cells

What is the spontaneous firing rate of the vestibular nerve? Why is it non-zero?

70-100 spikes per minutes

High SFR and non-zero firing rate means that inhibition can be encoded, provides mechanism for co-planar stimulation

What does the superior vestibular artery supply?

horizontal SCC, anterior SCC, utricle

What vestibular end organs does the common cochlear artery supply?

posterior SCC, saccule

What are the vestibular nuclei?

superior, medial, lateral and inferior

What brain structure are the superior and lateral VN connected to?

Cerebellum

What is the output of the cerebellum?

reticulospinal tract, lateral vestibulospinal tract, reticular formation

heavily involved in motor control

What is the reticular formation?

Uses information primarily from otolith organs and descends length of spinal cord

What are the thalamocortical projections?

information from vestibular nuclei ascends to thalamus, further projects to perietoinsular vestibular cortex (PIVC)

What is the PIVC?

Parietoinsular vestibular cortex

Major integration site for vestibular, visual, and motor system information

What is the VOR? What does it do?

Vestibulo-ocular reflex

Enables visual stability during motion; SCCs to extra ocular muscles to provide equal and opposite eye movement in response to a head turn

Describe the VOR from the right lateral SCC

right lat SCC, right superior vestib nuclei, left CN VI nucleus

left CN VI nucleus to left lateral rectus

left CN VI nucleus to right CN III nucleus (via MLF) to right medial rectus

How is the lateral SCC evaluated? (what tests)

calorics, rotary chair, head impulse

*also oVEMP for utricle translational VOR

What is the vestibulocollic reflex?

enables head to remain still during movement

What is the VCR pathway?

saccule, inferior branch of vestibular nerve, medial VN, CN XI, trapezius and sternocleidomastoid (SCM) muscles

What is the vestibulo-spinal reflex? How is it evaluated?

triggers uper and lower limb responses to changes in balance

Romberg, computerized dynamic posturography

What is nystagmus?

rapid, involuntary eye movements

What does the slow phase of the nystagmus correspond to? What is the fast phase?

Slow phase: vestibular system information

Fast phase: compensatory reset saccade to bring eyes back to midlines

How is nystagmus defined? How is it measured?

Defined by fast phase

Measured/quantified by slow phase

What is electronystagmography?

Measures corneoretinal potential with electrodes placed around eyes to record electrical activity

Not done as much anymore due to advances in video recording (used in videonystagmography, VNG)

What is the spontaneous vestibular nystagmus test? How is the test conducted? What do the findings indicate?

Used to identify a static imbalance between right and left peripheral vestibular systems

Observe eyes for nystagmus in vision and vision-denied conditions

Normal = no nystagmus in either condition

Abnormal = nystagmus, determine if it follows Alexander’s law

What is head impulse testing? How is the test conducted? What do the findings indicate?

Used to identify VOR dysfunction

Examiner moves patient had in low-amplitude, high-velocity head turns; observes the patient's eyes for loss of visual fixation

Normal = no loss of fixation

Abnormal = loss of fixation; patient demonstrates a catch-up saccade to regain fixation

What is the headshake nystagmus test? How is the test conducted? What do the findings indicate?

Used to identify asymmetrical neural integration of VOR; measure of compensation

Patient oscillates the head for 25 cycles at 2 Hz vision denied

Normal = ≤ 3 beats of post headshake nystagmus

Abnormal = > 3 beats of post headshake nystagmus, fast phase typically beats toward the better ear

What is the dynamic visual acuity test? How is it conducted and what do the findings indicate?

Used to identify oscillopsia with head movement

Patient reads to the lowest level on an eye chart with the head stable and with the head oscillating at 2 Hz

Normal = ≤2 lines of change on the eye chart

Abnormal = >2 lines of change on the eye chart

What is the Valsalva induced nystagmus test? How is the test conducted and what do the findings indicate?

Used to identify the effect of intracranial pressure change on nystagmus

Patient increases in intracranial pressure by performing Valsalva maneuver for 10 to 15 seconds

Normal = no dizziness or nystagmus

Abnormal = conjugate eye movement towards the contralesioned ear; nystagmus dizziness

What is the modified clinical test of sensory interaction on balance (mCTSIB)? How is the test conducted and what do the findings indicate?

Used to measure postural control under various conditions

Patient instructed to maintain balance for 30 seconds in four conditions

1) eyes open, firm surface

2) eyes closed, firm surface

3) eyes open, foam surface

4) eyes closed, foam surface

Normal = ability to maintain balance in all conditions for 30 seconds

Abnormal = inability to maintain balance in all conditions for 30 seconds

Compared to age-specific normative values

What is the Romberg test? How is the test conducted? What do the findings indicate?

Used to measure postural control under various conditions

For 30 seconds in two conditions

1) eyes open, firm surface

2) eyes closed, firm surface

Normal = ability to maintain balance in all conditions for 30 seconds

Abnormal = inability to maintain balance in all conditions for 30 seconds

What is the gate speed test? How is it conducted and what do the findings indicate?

Used to measure functional mobility

Patient walks at comfortable and fast speeds for 3-10 meters

Gate speed equals distance/time

Normal values vary by age, gender, use of assistive device, and walking speed

What is the timed up-and-go (TUG) test? How is the test conducted and what do the findings indicate?

Measures functional mobility

Patient transitions from seated to standing, walks a 3 meter line, turns around, and sits down

Normal ≤ 13.5 seconds

Abnormal > 13.5 seconds

What is the dynamic gait index (DGI) test? How is the test conducted and what do the findings indicate?

Measure of balance in dynamic conditions

Patient completes a series of balanced tasks gate on level surface

1) change in gait speed

2) gait with horizontal head turns

3) gait with vertical head turns

4) gait and pivot turn

5) step over obstacle

6) step around obstacle

7) steps

The examiner scores the patient's ability using a rubric

What are the three major components of VNG testing?

oculomotor assessment, positional/positioning assessment, calorics

What is gaze testing?

Evaluate’s patient ability to maintain gaze on a target in primary gaze and in eccentric positions in both vision/fixaztion and in vision-denied conditions

What criteria is used to identify significant nystagmus?

1) nystagmus present in any gaze position with velocity > 5°/s

2) nystagmus present in four or more conditions with velocity < 6°/s

3) nystagmus present sporadically in all gaze positions with velocity < 6°/s

$) direction changing nystagmus within any gaze position

What are the oculomotor subtests? What is their function?

Gaze w/ and w/o fixation - hold image stable when head is still

Saccades - quickly move eyes to fixate on object of interest

Smooth pursuit - hold/track moving object with eyes

Optokinetic nystagmus (OKNs) - maintain clear vision when head or target is in constant motion

What are the positional/positioning subtests? What is their function?

Static positional recording in 4-6 conditions: supine, head right, head left, lateral right, lateral left, caloric test position (elevated 30°) - evaluates effects of head orientation and neck position on spontaneous nystagmus

Dix-Hallpike - tests for BPPV

Lateral head roll test - tests for BPPV

What is the function of caloric testing?

Assesses peripheral VOR performance in plane of lateral SCC; gold standard for identifying unilateral peripheral weakness

What is Alexander’s law? (3 components)

1) spontaneous nystagmus after peripheral vestibular insult has fast phase directed towards healthy ear

2) spontaneous nystagmus is:

a) greatest when gaze is directed toward fast phase (healthy ear)

b) attenuated in center gaze

c) may be absent when directed towards slow phase (lesioned ear)

3) spontaneous nystagmus is reduced with fixation and enhanced with vision denied

What is spontaneous nystagmus defined by?

Number of gaze positions it is present in

Ex: spontaneous nystagmus only present in gaze left = first-degree nystagmus

What are saccades?

conjugate eye movements that reposition the fovea on the target of interest

What is a random saccade paradigm?

saccade location, inter-saccadic interval and fixation duration are random

What brain regions/structures are involved in random saccade performance?

Frontal eye fields, brainstem, midbrain, superior colliculus, cerebellum, frontal lobe, posterior parietal cortex, basal ganglia, thalamus

What are the three parameters for saccade analysis?

Latency - time between presentation of target and initiation of eye movement

Accuracy - how far was the eye over or under the target

Velocity - how fast the eye moves toward the target once initiated

What does reduced velocity in both eyes during saccade testing indicate?

Fatigue, medications

Abnormal performance of reticular formation, MLF, cerebral hemispheres, superior colliculus, cerebellum

What does reduced velocity in one eye or restricted direction during saccade testing indicate?

Abnormal performance of reticular formation, MLF

Question INO (especially if slow adduction)

What does enhanced velocity during saccade testing indicate?

Calibration error

Restrictive syndromes, late myasthenia gravis

What does hypometria (undershoot) during saccade testing indicate?

Fatigue, medications

Bidirectional: cerebellar dorsal vermis

Unidirectional: ipsilateral cerebellum/brainstem

What does hypermetria (overshoot) during saccade testing indicate?

Cerebellum

What does prolonged latency in both eyes in all directions during saccade testing indicate?

Fatigue, medications

Superior colliculus, reticular formation

What is the typical latency for saccade testing?

Between 150-200 ms

What is the typical peak velocity for saccade testing?

300°-700°/s

Higher velocit expected with further distance to target from current eye position

What is smooth pursuit?

allows eyes to hold slow moving target of interest on fovea

What is needed for interpretation of smooth pursuit?

Need age-specific normative data

What is smooth pursuit the most sensitive oculomotor subtest for?

Cerebellar dysfunction

What parameters is smooth pursuit evaluated by?

Velocity gain - peak eye velocity/peak target velocity

Asymmetry - diff in velocity gain between rightward and leftward eye movements

Phase angle - how much eyes are ahead (leading) or behind (lagging) the target

Saccadic component - how much patient uses saccades instead of smooth pursuit to follow the target

What does an abnormal velocity gain during smooth pursuit testing indicate?

Increased saccadic movements

Could relate to:

a) acute peripheral vestibulopathy with active spontaneous nystagmus

b) brainstem or cerebellar lesion

What does asymmetric velocity gain on smooth pursuit indicate?

involvment of ipsilateral cerebellum, brainstem or parieto-occipital region

What is optokinetic nystagmus testing measuring?

Smooth pursuit and neural substrate encoding moving visual stimuli

As visual stimuli move: eyes should generate nystagmus response comparable to velocity of visual field

To measure OKNs, what % of visual field must the stimuli fill?

> 90%

What is the least sensitive oculomotor subtest for central pathology?

OKNs

What parameters are OKNs evaluated by? What are the normative values?

Velocity gain - peak eye velocity/peak target velocity

should be > 0.5 of target velocity

OKN generally reported as present or abnormal

What is the positional assessment in VNG testing?

Tests for presence of nystagmus in various head positions in relation to gravity

nystagmus may occur with or without sensation of dizziness

What could observed nystagmus during positional testing indicate?

Impaired SCC(s), impaired otolith organ(s), central vestibular pathways

Asymmetrical peripheral or central vestibular performance

Alcohol consumption, some medication use

What positions are done for oculomotor positional testing?

Supine, head center

Supine, head right

Supine, head left

Caloric test position (recumbent, head center and elevated 30°)

Optional:

• Lateral, body right

• Lateral, body left

• Head hanging, center

• Head hanging, right

• Head hanging, left

What criteria is used to assess if the visualized nystagmus is significant during positional testing?

Nystagmus present in any position with velocity > 5°/s

Nystagmus present in 4 or more position with velocity < 6°/s

Nystagmus sporadically present in all positions with velocity < 6°/s

Direction changing nystagmus noted in any position

What nystagmus in positional testing is NOT deemed a significant/novel finding?

Nystagmus with same velocity and direction as the nystagmus observed in gaze testing (ie the positional testing nystagmus is consistent with the spontaneous nystagmus)

What is direction fixed nystagmus?

Nystagmus with one direction regardless of position

Nystagmus that changes direction with head position is referred to as…?

geotropic or ageotropic

What is geotropic nystagmus?

nystagmus that beats towards the ground (fast phase to ground)

What is ageotropic nystagmus?

nystagmus that beats away from the ground

Are geotropic/ageotropic nystagmus direction changing?

NO! It changes direction with head position but is consistent within the same head position

What is the most common type of peripheral vestibular system pathology?

positionally provoked dizziness

Abnormal caloric findings are associated with what?

peripheral elsion involving lateral SCC and/or superior branch of the vestibular nerve on the side with the weaker response

What type of caloric irrigation is considered more reliable? Pros and cons of this irrigation type?

Water

Pros: less room for technical/user error, more robust stimulus, requires shorter irrigation time

Cons: cannot use with TM perf

What is the expected pattern of nystagmus during caloric testing?

warm irrigations - ampullopetal - excitatory - nystagmus beats towards irrigated ear

cold irrigations - ampullofugal - inhibitory - nystagmus beats towards non-irrigated ear

COWS

When does nystagmus peak during caloric testing?

30 seconds after irrigation is complete

60 sec for water, 90 sec for air

What is the stimulus temperature for water and aircalorics?

Water: Warm 44° Celsius; Cold 30° Celsius

Air: Warm 50° Celsius; Cold 24° Celsius

Why do you need to provide a fixation light during caloric testing?

To document fixation index (ability to suppress nystagmus with fixation and increase in velocity without fixation)

What % should nystagmus reduce by with fixation?

should reduce by 60%

What value do you need to record for each caloric irrigation?

Peak nystagmus velocity

What is unilateral weakness on calorics?

difference in peak velocity between ears

How is unilateral weakness calculated?

Jongkee’s formula

CP = [(right warm + right cool) - (left warm + left cool)] / (right warm + right cool + left warm + left cool)

What % CP is abnormal?

Abnormal CP >25%

Abnormal unilateral weakness on calorics is indicative of what?

peripheral vesitbulopathy

Rule out: poor irrigation, cerumen blocking ear canal, surgical ear, ear drum perf

What is bilateral weakness on calorics?

AKA bilateral areflexia or hypofunction

Reduced caloric response in each ear

How is bilateral weakness calculated?

Total eye speed

Right TES: right warm + right cool

Left TES: left warm + left cool

What TES defines bilateral weakness on calorics?

Each ear TES <12°/s

What is a bilateral weakness on caloric indicative of?

bilateral peripheral vestibulopathy (eg ototoxicity) or central vestibulopathy (cerebellar degeneration)

Rule out: poor irrigation, cerumen, surgical ear, use of vestibular suppressant meds (meclizine)

What tests should be done in conjunction with calorics to confirm bilateral weakness?

rotary chair, vHIT, mCTSIB/balance testing, ice-water caloric irrigations

How is caloric hyperfunction defined?

each ear TES > 140°/s

What is caloric hyperfunction associated with?

loss of VOR inhibition in vestibular nuclei or cerebellum

Rule out: TM perf, altered mastoid

What is directional preponderance?

comparison of right-beating vs left-beating nystagmus

How is directional preponderance calculated?

Calc TES for each nystagmus direction

• right-beating: right warm + left cool

• left-beating: left warm + right cool

Calc DP

DP = (right-beating - left-beating) / (right warm + right cool + left arm + left cool)

What directional preponderance is abnormal?

Abnormal DP > 30%

Also document which direction is stronger

What does an abnormal directional preponderance indicate?

Most often abnormal in those with underlying spontaneous nystagmus

W/o underlying spontaneous: consider technical error or non-localizing finding