Caloric Testing Flashcards
Are calorics generally though of as the most informative subtest of the ENG/VNG?
Yes
Are calorics the only test where we can isolate one vestibular organ?
Yes
A big advantage is that the physiologic integrity of the left and right peripheral system can be directly assessed
Is a caloric a primarily vestibular response?
Yes
Think end organ or 8th nerve
Fairly localizing
Might rarely see something from central affecting it
How are irrigations performed?
With cold and warm water or cold and warm air
Water: cool - 30 degrees C, warm - 44 C
Air: cool - 24 C; warm - 50 C
What does COWS mean?
Response pattern for calorics
cold opposite, warm same
Cold R ear = LB
Cold L ear = RB
What are the time intervals for calorics?
30 seconds for water
A minute for air
Is endolymph sensitive to temperature?
Yes
Can either makes it like water or like honey
Do the majority of people feel vertigo when we do calorics?
Yes
What is the advantage to air?
Cleaner
Can be done on kids
Can be done on someone with a PE tube or perf
More tolerable for the patient
What is the advantage to water?
A little more forgiving with placement
Will go right through wax or debris in the canal
Will typically get a bigger response with water bc it is a more aggressive stimulus
*Need to be much more cautious with air
Are nystagmus results are calculated to obtain unilateral weakness and directional preponderance?
Yes
UW (unilateral weakness/caloric paresis) - compares strength of responses in right ear and left ear
DP (directional preponderance) - compare right-going eye movements to left-going eye movements
Does the majority of the stimulus from the caloric come from the horizontal canal?
Yes
Because when you lay a patient back (recline) the horizontal canal is perpendicular to the ground
What are some disadvantages to caloric testing?
The actual level of stimulation at the end organ may vary greatly due to the heat-transferring capabilities of the surrounding bone and air (lots of barriers to go through)
It is a low frequency stimulus (0.003-0.005 Hz) so it’s not very applicable to the real world (no one is actually moving that slow)
Only looks at a small portion of the anatomy (horizontal SCC - SVN and central)
Is low frequency stimulus more sensitive to mild vestibular damage?
Yes
Might not show up on high frequency stimuli yet
What happens when you put something cooler than body temp in the ear?
The fast phase of the resulting nystagmus is directed toward the opposite ear
When warmer than body temperature is used a nystagmus with a fast phase toward the irrigated ear is elicited
Is the nystagmus for calorics a jerk nystagmus?
Yes
How do you reference UW and DP?
UW - reference weak one
90% R UW
DP - reference stronger one
30% L DP (left eye movements are stronger)
What is fixation suppression?
Response caused by the cerebellum
Nystagmus suppressed with light or something to fixate on (normal)
How do you calculate unilateral weakness?
((RW+RC)-(LW+LC))/(RW+RC+LW+LC) x 100
What is a abnormal UW?
25% or greater is abnormal
How do you calculate directional preponderance)
((RW+LC)-(LW+RC))/(RW+RC+LW+LC) x 100
What is the norm for DP?
35% or greater is abnormal
How do you calculate fixation index?
SPV (eyes open)/SPV (eyes closed)
*SPV=slow phase velocity
What is fixation index?
Used to assess the intactness of connections between the vestibular nuclei and the midline cerebellar structures
What does peripheral mean for calorics?
Refers to any point distal to the second-order neuron in the VOR arc, (that is, originating at the level of the vestibular nucleus)
Thus, a unilateral weakness can be caused by damage occurring within the vestibular end organ, the vestibular portion of the VIII N, or the root entry zone of the VIII N
What is the most common cause of unilateral weakness?
End organ disease
UW of peripheral origin may also be caused by bacterial destruction of the membranous labyrinth that occurs in congenital, secondary, and tertiary syphilis and in bacterial meningitis that leads to Labyrinthitis
Can UW of vascular origin occur?
Yes
In migraine and in cerebrovascular disease affecting the posterior circulation
What are the results for individuals with neural origin?
The patient does not complain of hearing loss or tinnitus or other neurologic symptoms
The caloric examinations of these patients show a total absence of response or a marked UW
The most common neural origins of UW the acoustic neuromas (and other tumors of the cerebellopontine angle) and vestibular neuronitis
Less common neural origins of UW are demyelinating diseases
What are the results for individuals with central origin?
Demyelinating disease can affect the 8th nerve or the vestibular nuclei
The effect of the disease is to slow conduction through the nerve or brain stem, and in its severest form to block neural conduction completely
Brain stem disease has also been shown to cause UW
The types of brain stem diseases include infarctions, demyelinating disorders and degenerative disorders and tumors
When is the total response normal?
Greater than 20 or 26 degrees per second
When is fixation suppression normal?
Varied
Greater than 50% or more
Is DP most often seen in patients who have a strong spontaneous nystagmus?
Yes
Not surprising that these patients demonstrate caloric responses that are stronger for irrigations that result in nystagmus beating toward the direction of the spontaneous nystagmus
We don’t want to know what we already had going into the test, only what was stimulated
Need to measure what you had before and cross check
Alternatively, these patients demonstrate weaker responses when the caloric nystagmus is beating against the direction of the spontaneous nystagmus
If you get a reduction, will the responses be reduced for both warm and cold results?
Yes
Are DPs non-localizing?
Yes
The presence of a DP indicates a tonic bias in the vestibular system which could be caused by peripheral (end organ and VII N) or central (brain stem and cortex) disease (non-localizing)
In some cases a DP may be found in otologically normal subjects
What is bilateral weakness?
Operationally defined as total caloric responses less than 20-22 degrees/sec
Bilaterally reduced responses may be caused by drugs that distribute their effects bilaterally
May also be caused by systemic infections that have an effect on the vestibular end organ
What does CNS disease produce?
Either produces bilateral reduction or bilateral absence of caloric responses
This may occur due to damage occurring at the level of the vestibular ganglion, VIII N, or vestibular nucleus
What is Bell’s phenomenon?
Refers to the reflex averting (rolling up) and adducting (moving laterally toward one another) of the eyes that occur upon eye closure
ENG only (eyes closed)
What are hyperactive caloric responses?
Caloric-induced nystagmus which exceeds the upper limits of laboratory normative data
Total cool responses exceeding 80 degrees/sec and total warm responses exceeding 90 degrees/sec
How do hyperactive responses work?
The flocculo-nodular lobe of the cerebellum has fibers that project directly to the vestibular nuclei and have an inhibitory influence on vestibular neurons
Thus a major function of the flocculus is to inhibit the VOR
Therefore, lesions of the cerebellum produce an increased excitatory state of the vestibular nuclei because of a disruption of the regulatory influence of the cerebellum
Are hyperactive responses uncommon?
Yes, extremely
May result from inorganic sources
Enhancement of caloric transfer due to mastoidectomy, perf, atrophy, or retraction of the TM
Excessive nervousness or overalertness
What is stimulating the cerebellar flocculus?
a climbing fiber pathway from the inferior olive, and
a mossy fiber pathway from the superior colliculus
What information does the flocculus get?
eye position and eye velocity during pursuit activities
Has it been demonstrated that the fixation suppression requires participation of the pursuit system?
Yes
There is a known close relationship between the upper limits of smooth pursuit velocity in a given individual and the upper limit of FS during rotary stimulation
What are the 3 patterns of FFS abnormalities?
Bilateral FFS (associated with diffuse disease affecting the CNS)
Unilateral FFS
FFS non-affected ear
What is caloric inversion?
An entire caloric response that beats in the opposite direction to that expected
Caloric inversions are rare and have been associated with brain stem disease
What must we consider if there is caloric inversion?
The most common source of technical error occurs when the electrode leads have been plugged in incorrectly
The examiner must determine whether a strong positional, spontaneous, or congenital nystagmus exists that is beating opposite to the expected direction of the caloric response
Caloric inversions must be viewed with caution when air stimulation is used in the presence of a large tympanic membrane perforation (causes evaporation of moisture in the mucosal lining of the middle ear - creating a cooling effect instead)
What are caloric preversions?
The generation of an oblique or vertical nystagmus following stimulation of the horizontal semicircular canal during caloric testing
This phenomenon has been linked to disease affecting brain stem structures at the floor of the fourth ventricle (most likely the medial and superior vestibular nuclei)
When is ice water used in caloric testing?
For instances when alternate bithermal caloric testing (ABB) yields no recordable responses
When evaluating nystagmus obtained from the ABB test do not assume that the absence of a response reflects no vestibular function in the horizontal semicircular canal
May respond to ice water instead
Who first described calorics?
1906 by Dr. Barany
Physician and later Professor of otorhinolaryngology at the University of Uppsala, Sweden from 1926 to 1936
Considered by many as the father of neurotology
Irrigating wax from patient’s ears using different temperatures and he noticed nystagmus with different directional nystagmus features
Received a nobel prize
Can caloric testing also be used to assess for brainstem death?
Yes
Brainstem is critical for cardiac and respiratory function as well as CNS regulation (consciousness and sleep cycle)
Squirt ice water into the ear, if there is nystagmus, the brainstem is alive
If not, the brainstem is so damaged that they are not expected to get better
What are variants of the caloric test?
Bi-thermal water test (the standard); bi-thermal air
Mono-thermal test - a single large bolus of ice water is given rather than two irrigations with hot and cold OR
Bilateral irrigation - both sides are irrigated simultaneously (hard to carry it out at the same time - theoretically should cancel each other out, so there shouldn’t be nystagmus)
Balloon test - a water filled balloon is used instead of water (will not get as big of a response as just open water or air)
Ice water caloric - used to confirm complete loss
Do you get a bigger response the further you get away from normal body temperature?
Yes
What is the caloric position?
Supine, head elevated 30deg, vision denied
HSCCs are now perpendicular to ground
Is tasking important for calorics?
Yes
Prevents them from suppressing their eye movements
Should you do two irrigations in a row that beat the same way?
No
Generally ok to start with cools and then go to warms, but make sure they don’t go the same way back to back
How does temperature affect endolymph density?
Warm stimulation = decreased endolymph density = ampullopetal flow = excitatory response for test ear
Cool stimulation = increased endolymph density = ampullofugal flow = inhibitory response for test ear
*always referencing the same ear
What does unilateral weakness indicate?
Pathology on the weaker side
What is the significance of directional preponderance?
Non-localizing finding
Low diagnostic utility
Most commonly seen with pre-existing spontaneous nystagmus or w/ asymmetric responses due to poor irrigation
What are the formulas called for UW and DP?
Jongkee’s
How do you calculate the total response/total eye speed?
RC+LC+RW+LW
What is hypo-responsive?
Comparison of total responses from both ears
Less than or equal to 26 degrees/second is abnormal
May indicate bilateral vestibular loss (non-localizing finding), but it is not definitive
Rotary chair is the only way to diagnose bilateral vestibular loss
Be cautious of the patients alertness (including meds) and tasking because this could cause this
What is hyper-responsive?
Comparison of total responses individually
Greater than or equal to 140 degrees per second is abnormal
Can indicate a central finding (cerebellar), but it is very rare
Rule out technical stuff first
Could have potentially CNS pathology, but there would be other indications of this before calorics
What are some limitations of calorics?
Only test VOR at a very low frequency (very slow head movement, where the VOR doesn’t perform optimally)
Only tells us about function in HSCC and SVN
Variable and slightly uncomfortable
Can’t be performed/evaluated on some patients (young kids, microtia/anotia, surgical ears (perf, PE tube))
Can infer but not definite for bilateral vestibular loss (BVL)
Cannot determine the level of functional compensation (rotary chair can)
When are ice water calorics done?
Used when bi-thermal irrigations are very low or to help conform diagnosis of BVL though rotary chair is gold standard
Is there a standardized procedure and temperature for ice water calorics?
No
Typically a single bolus approximately 2cc of ice water (~18℃) is delivered to the ear
Can be in traditional caloric position or supine head rotated and held before returning to caloric position or prone
Does compensation happen fairly quickly after unilateral vestibular damage?
Yes
The resting neural activity on the damaged side decreases
This is why we can measure a caloric weakness on that same side
This is also why ‘perceptually’ the person experiences vertigo
The cerebellum will pull down the other side and the acute symptoms will go away
How does central compensation happen?
The first step in the central compensation process involves “clamping down” on the resting neural activity on the un-injured side at the vestibular nuclei (to minimize the tonic imbalance)
This clamping reduces not only the asymmetry of the VOR pathway but also serves to help improve the patient symptoms (decreased vertigo)
Over time (days-weeks) the clamping on the good side lets up as the resting activity is restored to the vestibular nuclei on the damaged side
Once static compensation is achieved the spontaneous nystagmus will disappear and the patient’s symptoms will improve as long as their head remains still
Head motion at this point will still provoke symptoms though
The last stage of compensation is called dynamic compensation and involves reprogramming of the VOR pathways to deal with the long-term effects of labyrinthine loss on the damaged side
Only after dynamic compensation will the individual functionally return to normal
The caloric test will ALWAYS show the weakness throughout the whole process and from there forward (permanency)
What is required to have good compensation?
An intact cerebellum (flocculus and paraflocculus)
And use of limbs
What should you do if a patient has an abnormal finding on an oculomotor exam?
Reinstruct and repeat it
True abnormal will always remain abnormal
Should you wait between irrigations?
Yes
Make sure there is no nystagmus and the patient is not feeling dizzy
What are the codes for VNG?
CPT 92540 - basic vestibular eval (all oculomotor testing and positional testing)
CPT 92537 - caloric with recording bilateral, bithermal
CPT 92538 - caloric with recording bilateral, monothermal (one irrigation for each ear, instead of two)
What are the codes for ENG?
Same as VNG
May also bill CPT 92547 - use of vertical electrodes for recording purposes to reflect time to place electrodes
What can you do if you cannot bill the entire ENG/VNG test?
Bill individually
CPT 92541 - Spontaneous nystagmus test, including gaze and fixation nystagmus, with recording
CPT 92542 - Positional nystagmus test, minimum of 4 positions, with recording
CPT 92544 - Optokinetic nystagmus test, bidirectional, foveal or peripheral stimulation, with recording
CPT 92545 - Oscillating tracking test, with recording
Add the -59 modifier if bill two or three of 92541, 92542, 92543, or 92544 on the same patient on the same date of service
CPT 95992 Canalith Repositioning Procedure(s) (e.g., Epley maneuver, Semont), per day
*All codes single unit and can only be billed once per date of service
What determines how fast it returns to normal?
Depends on the intensity of the response and the sensitivity of the system (vestibular system stores it like a battery)
