Head Impulse and Video Head Impulse Testing (vHIT) Flashcards
What are symptoms of impaired VOR?
Head and eye coordination out of sync
Visual blurring, bouncing (oscillopsia, retinal slip)
Trouble reading signs when walking
Head turns while at a stop or in a grocery store (type of stimulation in a busy area tends to bother them)
What is vHIT?
It is an instrumented version of the halmagyi head thrust
Altered VOR gain and presence of re-fixation or catch-up saccades in abnormal individuals during head thrust
Uses sophisticated eye tracking and head velocity transducers to quantify gain measures and detect both covert and overt re-fixation saccades the former which cannot be seen without sophisticated recording equipment
What curves do you look at for vHIT?
Head and eye impulse graphs
What are the two types of refixation saccades?
Covert = Saccades that occur during the head movement; difficult to impossible to see with the naked eye
Overt = Saccades that occur after the head movement; can be seen with the naked eye
When did the first commercial vHIT systems come out?
2015
GN ICS-Otometrics
Interacoustics
Micromedical
Synapsys (no goggle, tower mounted in front of the person)
Diffra
In addition to eye cameras, what else do vHIT systems have?
Head velocity sensor
Does each vHIT system have different analysis patterns?
Yes, gain values found to be widely varied between systems in normals
Types: PG is position gain, IG is instantaneous gain, and AG is area under the curve gain (similar to position gain).
Position gain is the Visual Eyes device from Micromedical, Instantaneous gain is the EyeSeeCam device from Interacoustics, and Area under curve is the “Impulse” device from GN Otometrics
*each has different normative data based on the analysis that they use
How to perform vHIT?
Patient keeps eyes focused on fixed point
Head moved rapidly (200+degrees/second), 10-20 deg range only
Keep unpredictable
Can be performed from 10 months old to elderly
What is normal?
Eye should remain on the target
Head movement and eye movement should be roughly equal and out of phase
What is abnormal VOR?
Eyes may lag behind head movement and require re-fixation/catch-up saccade
Is the head moved in the plane of a specific canal?
Yes
Horizontal = right and left
RALP = right anterior and left posterior
LARP = left anterior and right posterior
What two things are analyzed with vHIT data?
Gain = eye movement relative to head movement (normative >0.7 some systems, >0.8 other systems)
Presence of re-fixation saccades (overt and covert)
What is the clinical usefulness of vHIT?
Functional measure
Evaluates high-frequency reactivity
Gives canal specific information
High sensitivity to vestibulopathy
Can help track VRT progress and compensation (rehab)
What are some limitations to vHIT?
vHIT only analyzes high-frequency deficits (might miss low frequency vestibular deficits - which is typically affected first)
Some research has suggests insensitive to dysfunction secondary to Meniere’s disease (more of a pressure problem)
Technique can be very challenging
Can you be very site specific with vHIT?
Yes
Did they think that vHIT would replace calorics?
Yes
But there is no code for it (not reimbursed by insurance), there is a code for calorics
And it doesn’t assess mild losses (low frequency)
Results do not always correlate
vHIT does have really good specificity compared to calorics
The nature of the test is just different
Are calorics generally not as tolerable to people as vHIT?
Yes
What are the vHIT findings for vestibular neuritis, menieres disease, concussion, and labyrinthitis?
Reduced gain and corrective saccades
What is the vHIT findings for BVD?
Reduced gain and corrective saccades bilaterally
What are backup saccades?
Anti-compensatory or reversed saccades
Central sign, typically cerebellar
Covert anti-compensatory eye movement during head impulse seen in migraine and in Meniere’s
If you have high gain only and no re-fixation saccades, it’s usually a technical error
What is the HINTS protocol?
Used to separate out benign vestibulopathy and stroke patients
PRO: More sensitive (<24 hours) and less costly than early stage MRI for stroke (and cheaper and faster)
CON: Requires expertise not routinely available in E.R.
*Looking at the function than the structure itself
Are only a small number of patients with vertigo/dizziness attributed to stroke?
Yes
About 4%
Although a lot of these patients have a high risk factor for stroke
MRIs are expensive, so this is a better alternative to catch the small percentage who actually had a stroke
What is AVS?
Severe continuous dizziness/vertigo, nausea, vomiting, gait instability, head motion intolerance and nystagmus that can last up to weeks
Most AVS patients have benign peripheral cause such as vestibular neuritis, non-bacterial labyrinthitis
Up to 25% can have brainstem or cerebellar strokes
Distinguishing peripheral from central can be tricky particularly in acute setting and E.R.
Half of stroke patients with AVS have no focal neuro signs
In the first 24 hours post-stroke, can CT scan accurately detect cerebellar hemorrhages?
Yes, but not ischemic strokes
Do structural anatomic changes from brain ischemia generally lag physiological dysfunction?
Yes
HINTS 100% sensitivity
96% specificity
What does HINTS stand for?
Head Impulse: negative - central, positive - peripheral
Nystagmus - in-between
Test of Skew (cover one eye; when you pull it down, you can get skew deviation): negative - peripheral, positive - central
How to test skew deviation?
Have patient look at your nose with both eyes then cover one eye
Then rapidly uncover the eye and quickly observe to see if the eyes move to re-align
Repeat on each eye
If patient complains of binocular diplopia that is a positive test also
What are some central red flags?
Balance poorer than expected (consider age, vestibular status, etc.)
Mild vertigo/dizziness with intense nausea/emesis
No identifiable preceding vestibular-like event (usually not a lot of warning compared to peripheral)
Neurologic-type symptoms
Cardiovascular-type symptoms
What is the SHIMP variant?
VHIT variant where patients are asked to view a laser dot that moved with their head (head fixed target)
This protocol then asks patients to turn OFF their VOR, rather than to use it
The authors state that “anticompensatory” saccades are elicited in normal controls, but are less commonly found in persons who have less VOR to suppress
Patient will have overt catch up saccades
Is there currently a billing code for vHIT?
No
It’s a long process to get a code for a new test
How do you get paid for vHIT?
Bill 92700 - unlisted otorhinological item or service
Or just have the patient pay for it
