We continue to respond to questions posed by readers as we make our way through this quarantine. Andy, AuD asked the following question:
“I work in a multi-specialty private clinic here in the Caribbean. As our budget is somewhat limited, what diagnostic equipment is recommended or considered essential for establishing an appropriate vestibular clinic. We have family medicine and physiotherapy present, but no ENT physicians onsite.”
I think the best approach to answering this question is to frame it as “What tests are essential?’ and “What equipment is required to perform those tests?” The answer to these questions is not the same for every vestibular patient, and not every patient complaining of dizziness, vertigo, lightheadedness or imbalance is a vestibular patient.
So, let’s start with the type of complaint:
The most typical patient seen in the vestibular lab has complaints of episodic symptoms. They are typically asymptomatic on arrival. These patients can be broken down into two broad categories, provoked symptoms and spontaneous symptoms. Provoked symptoms most often last less than one minute, and are triggered by position change. This is applicable to both BPPV and Orthostatic Hypotension (OH). From a history standpoint, BPPV can trigger symptoms when you lie down, roll over and get up from bed. OH will not trigger symptoms when you lie down or roll over. A complicating factor is that many BPPV patients will tell you the symptoms are most severe when they first get up in the morning, presumably due to otoconia debris settling overnight.
Video goggles enhance the diagnosis of BPPV, but are not necessary. A sphygmomanometer (blood pressure cuff) can identify a drop in blood pressure on rising. Since the diagnosis of OH is not in the scope of audiology, we simply document our findings and forward them to the referring physician.
For patients with episodes of spontaneous vertigo lasting several minutes or more, the question is not so easy to answer. The two most likely causes for this complaint include Vestibular Migraine and Meniere’s disease. The accepted criteria for diagnosis of Vestibular Migraine includes “not better accounted for by another vestibular or ICHD diagnosis.” This brings up the question of what it takes to reasonably rule out a vestibular disorder. Some would say “a normal VNG”, but I disagree. Rotational Chair, vHIT and VEMPs will detect vestibular dysfunction in many patients with “a normal VNG.” That does not mean you can’t be effective for many patients without this equipment. You just can’t be effective for all of your patients.
For Meniere’s patients, the most important piece of equipment is your audiometer. Documenting fluctuating low frequency sensorineural hearing loss on the affected side is more diagnostic than any vestibular test. Rotational Chair and vHIT are often normal in Meniere’s patients (which is why they are usually asymptomatic in regards to vestibular symptoms between episodes), but a caloric hypofunction is often the only abnormality in early Meniere’s.
The HINTS protocol (which requires no special equipment) has been shown to be an effective technique to assess patients presenting while acutely vertiginous. This requires an examination for nystagmus, which benefits from an effective method of reducing visual fixation, and assessing the impact of visual fixation on nystagmus intensity. Infra-red video goggles are, by far, the most effective technique to accomplish this.
In the most acute phase of a vestibular neuritis (say the first 24-48 hours when the HINTs exam is most applicable) nystagmus may be visible without goggles, but after that goggles are usually needed to detect spontaneous or gaze nystagmus.
Head Thrust versus vHIT for VOR Deficit
The idea behind vHIT is to establish whether the eyes are accurately reflexively responding to impulsive head movement. Latency of response (measured as overt or covert saccades) and gain can be assessed. The bedside Head Thrust test focuses on the identification of overt saccades. So, some high frequency VOR deficit can be identified without vHIT equipment, but vHIT is more sensitive. There appears to be a significant learning curve related to the Head Thrust exam, as vestibular specialists find it far more helpful than do emergency department physicians.
Another method of assessing the high frequency VOR includes Dynamic Visual Acuity testing, which requires only a Snellen chart and some experience. The most sensitive test of VOR function is a rotational chair. Not only does it measure the VOR at real life head speeds, central compensation after a vestibular injury can be tracked over time. The obvious downside to rotational chair is the cost of equipment, so it only makes financial sense in a practice dedicated to vestibular function testing.
Vibration versus Caloric Irrigation
The idea behind both of these tests is to provoke nystagmus as a means of identifying labyrinth/vestibular nerve asymmetry. Neither test provides any information about central compensation or VOR function at real life heads speeds. Caloric irrigation requires expensive equipment and takes 25 to 45 minutes, and often triggers nausea. Vibration equipment is under $40 and takes less than a minute, rarely triggering nausea.
For more on this, read this article we recently published in Audiology Today.
VEMPs versus Knowing Someone Who Does VEMPs
VEMP testing is critical in patients with suspected Superior Canal Dehiscence, and helpful in patients with suspected Labyrinthitis/Neuritis. For this you would need evoked potential equipment. This will likely be a small number of patients, so purchasing evoked potential equipment may not make financial sense. Like rotational chair, depending on patient volume, it may make more sense to seek out a resource for when these tests are needed.
There is so much benefit to using infrared video goggles that I would say they are essential and should be used on every patient. A blood pressure cuff and a vibration device are inexpensive items that will allow you to identify the problem in many patients. Despite your skill level with Head Thrust testing, vHIT will identify VOR dysfunction that is not visible to the naked eye. If you have an ABR unit, do VEMPs on patients with suspected SCDS or Labyrinthitis.