New Frontiers in Managing the Dizzy Patient

Summary

Despite progress in vestibular research in the last twenty years, much remains poorly understood about vestibular pathophysiology and its management. A shared language is a critical first step in understanding vestibular disorders and is under development. Telehealth will continue for patients with dizziness, and ambulatory monitoring of nystagmus will become a diagnostic tool. In the next two decades, we anticipate that vestibular perceptual threshold testing will become common in tertiary centers, that imaging with improved spatial resolution will yield better understanding of vestibular pathophysiology, and that vestibular implants will become a part of clinical practice.

In the last two decades, we have seen great progress in our understanding of the clinical management of patients presenting with dizziness or vertigo. The lifetime prevalence of dizziness has been estimated to be around 30%, with approximately 3% of adults experiencing dizziness in any year. True vertigo occurs much less often (21% and 1.4% respectively). In the United States, dizziness accounts for 4 million visits to emergency departments per year ^1–3. Dizziness symptoms or signs are more prevalent with increasing age, have been found to increase the risk of falls ⁴ and are associated with cognitive impairment ⁵, two of the most debilitating and expensive healthcare conditions in society. This data emphasizes the important public health aspects of vestibular disorders and the urgent need for better diagnosis and management. Despite progress, much remains poorly understood about vestibular pathophysiology and its management. The aim of this narrative review is to highlight key developments and research in vestibular disorders that are likely to be adopted in clinical practice in the next 20 years.

A Common Language for Dizziness and Associated Disorders

The use of language is a fundamental problem for vestibular disorders. Most vestibular disorders do not have a clinical test capable of establishing a diagnosis. Instead, when deciding on a diagnosis, clinicians rely primarily on the symptoms that a patient reports. Terms like ‘dizziness’ or ‘vertigo’ can have different meanings to patients and providers. Since vertigo occurs only when the vestibular system is not functioning properly, patients struggle to describe their new experiences, even as an adult. This challenge is magnified when clinicians define terms differently or when some common terms like vertigo do not translate well across languages. Furthermore, research studies use different diagnostic terms to describe patient symptoms or diagnoses, some of which are specific to regions or medical centers.

The Bárány society, an international organization of neurologists, otolaryngologists, engineers, scientists and rehabilitation specialists, has established the International Classification for Vestibular Disorders (ICVD) that aims to provide standard definitions of symptoms and signs of vestibular disorders and diagnostic criteria ⁶. Already, diagnostic criteria have been updated for Ménière’s disease ⁷, vestibular migraine ⁸, bilateral vestibulopathy ⁹, vestibular paroxysmia ¹⁰, benign paroxysmal positional vertigo ¹¹ and mal de debarquement syndrome ¹². Diagnoses that have had different criteria depending on the academic medical center such as persistent postural perceptual dizziness (PPPD) have been combined under a single diagnostic term ¹³. Some conditions like presbyvestibulopathy ¹⁴, a labyrinth analogue to presbycusis in the cochlea, and orthostatic dizziness ¹⁵ are now established diagnoses. Like the diagnostic and statistical manual (DSM) for psychiatric disorders, the ICVD organizes a common language for physicians and specialists, allowing them to communicate better about patients and to establish rigorous definitions for making progress in research.

New diagnostic criteria are being published for vestibular migraine of childhood and superior semicircular canal dehiscence syndrome, with others such as motion sickness, acute unilateral vestibulopathy, perilymphatic fistula, and labyrinthine concussion under development. The published definitions will be updated regularly as our understanding of these disorders and their pathophysiology improves. Clear diagnostic criteria have also led to understanding that dizziness disorders are often not seen in isolation ¹⁶. The ICVD diagnostic criteria are an essential foundation and will become even more integrated in the care of patients with dizziness.

Remotely Managing the Dizzy Patient

Clinicians have rapidly adopted telehealth, driven by the infectious risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and by measures to relax regulations and support reimbursement for virtual clinical encounters ¹⁷. For several years before SARS-CoV-2, the use of telehealth by otolaryngologists has increased ¹⁸. Emergency providers and neurologists have worked together to provide virtual evaluations of dizzy patients in the emergency setting ^19,20, promising improved resource utilization ²¹. During the SARS-CoV-2 pandemic, as many clinical medicine visits shifted to remote encounters, telehealth algorithms were developed and applied to outpatient visits for patients with dizziness ^22–24. Despite technical challenges related to software and network connectivity, patients and providers are satisfied with virtual visits, suggesting telehealth after SARS-CoV-2 is likely to continue at greater frequency than before the pandemic ²⁵.

Virtual visits are well-suited to diagnoses like vestibular disorders that are primarily based on patient symptoms and assessments of eye movements. However, we will need to develop algorithms to better triage patients for in-person visits. Patients with chronic dizziness symptoms consistent with vestibular migraine or PPPD for instance may be appropriate for a telemedicine visit before in-person evaluation. Some patients with new, persistent dizziness, however, are having a stroke and require urgent in-person assessment. Improved access to physicians via telemedicine may lead to patients with an acute vestibular syndrome seeing an otolaryngologist before an emergency medicine provider. Virtual evaluations of an acutely dizzy patient require video adequate for assessing eye movements ²⁶, an exam important for separating central from peripheral pathology ^19,27. Fortunately, this exam is readily accessible in a virtual visit, and standards for remote assessments of a dizzy patient are being developed ^23,26. Management may be possible as well, with evidence that vestibular rehabilitation is effective via telehealth ²⁸. While there are technical challenges to telehealth and virtual assessment of eye movements, these can be overcome with current technology ²⁴.

Event Monitoring for Dizziness Episodes

Many patients with vestibular disorders do not experience episodes of vertigo or nystagmus when seen in the office. Patients may be encouraged to keep a diary of their episodes; however, these provide limited information to the clinician aside from the duration and presence of an episode of dizziness. In other fields in which patients have paroxysmal symptoms such as cardiac electrophysiology or epilepsy, event monitors record physiologic data during an event, sometimes transmitting this data remotely for interpretation. A similar approach has been applied to patients with dizziness ²⁹, in which patients were provided goggles that were donned during episodes to record nystagmus. The eye movements were later processed and interpreted.

Event monitoring in episodic dizziness has diagnostic value and can be used with commercially available technology. Wearable technology such as electronic watches and heart rate monitors are diagnosing cardiac arrhythmias ³⁰. There has been similar interest in using widely available smartphone technology for eye movement analysis for vestibular diagnoses ³¹. Eye movement tracking using optical head-mounted displays is under development for commercial use. Similar to current partnerships with companies producing this technology for cardiac event monitoring, researchers could minimize barriers to development by collaborating with commercial developers.

Quantifying Vestibular Perception

Patients with vestibular disorders perceive dizziness or vertigo, yet there are no tests of vestibular perceptual thresholds used in the clinic. Tests of subjective visual vertical or horizontal are the closest to a currently available perceptual test. Patients align a bar with the assumed gravity vector or horizon. While not widely used in clinical practice, the tests have promise for assessing otoconial organ function. Inexpensive versions have been developed ³². The commonly performed vestibular assessments (rotary chair, caloric testing, video head impulse testing and VEMPs) are physiologic tests that measure performance of reflex pathways from the vestibular organs. Although these tests have advanced our ability to diagnose patients with dizziness, reflex pathway testing correlates poorly with vestibular symptoms ^33,34. This disconnect, in addition to the appeal of developing tests of perceptual limits like those used in audiometry, has led to renewed interest in perceptual testing of the vestibular system.

During perceptual threshold testing for the vestibular system, patients are seated in a chair, while low-velocity, low-acceleration motions are delivered via a motorized moving platform, sled, or rotary chair ^35–38. When the patient perceives motion, they signal the direction of movement. The semicircular canals and otoconial end organs can be tested using movements that are rotations (in the X ‘tilt-roll’, Y ‘pitch’, or Z ‘yaw’ axes) or translations (in the X ‘surge’, Y ‘heave’, or Z ‘bob’ planes). To the extent possible, patients are isolated from external visual, auditory, and somatosensory stimulation. The minimal perceptual threshold is found using the staircase method. Similar to assessing pure tone thresholds, at first the stimulus intensity is easily detected and then is decreased until the motion is imperceptible, at which point the intensity is increased again until a correct response is achieved, upon which it reverses again. Current testing protocols are time consuming, taking up to 100 trials to find the perceptual threshold for each motion vector, thus limiting its clinical application ³⁹. A testing protocol using a twelve-motion forced choice paradigm has recently been proposed as more suitable for clinical testing ⁴⁰.

Threshold testing can add perceptual information about vestibular performance that is direction and frequency specific. Higher thresholds have been observed in patients with bilateral vestibulopathy ⁴¹ and Meniere’s disease ⁴², while patients with vestibular migraine have lower thresholds ⁴³. Importantly, thresholds appear stable when repeated, suggesting they can be followed over time ⁴⁴. Similar to vestibulo-ocular reflex and VEMP responses, perceptual responses appear to decrease with age starting in the fifth decade ³⁹. Clinical testing procedures are needed that balance thoroughness with the time constraints of a clinical encounter. Studies are also needed on a wider variety of vestibular disorders and the response of testing to treatment. Although perceptual thresholds might intuitively correlate with patient symptoms and risk of falls, this needs to be demonstrated. If perceptual threshold tests correlate with symptoms, they are likely to become more common in tertiary clinical centers in coming years.

Seeing Pathology of the Inner Ear with Imaging

The labyrinth has been difficult to image because it is deep within the skull, tiny, and surrounded by a mixture of materials of different densities. Computed tomography (CT) provides vivid contrast between otic capsule bone and fluid or soft tissue structures, whereas magnetic resonance imaging (MRI) discriminates better among soft tissues of differing proton densities (i.e. water density), and has potential for imaging the membranous labyrinth. CT and MRI will continue to be complementary techniques in the management of patients with dizziness. There have been new technological developments in both CT and MRI that are aiding the diagnosis of patients with dizziness and are likely to see greater adoption in clinical practice.

Flat-panel CT scanners use a cone-shaped beam of X-rays and a sensor arranged in a flat panel. These scanners are widely used in dental offices, and are being used to image the inner ear, with spatial resolution exceeding that of conventional helical temporal bone CT scanners (Figure 2) ⁴⁵. For the diagnosis of thin versus dehiscent bone over the superior semicircular canal, images from flat-panel scans correlate better with intraoperative findings ⁴⁶. These scanners are also useful for improving CT image quality of inner ear implants ^47,48. As flat-panel CT scanners become more widely used by otolaryngologists and neurologists, we will learn more about disorders affecting the bony labyrinth. Any bony dehiscence of the otic capsule likely contributes to symptoms of a third mobile window ⁴⁹. Patients with a dehiscence of other parts of the inner ear such as the posterior semicircular canal and cochlea, as well as patients with a presumed inner ear dehiscence, but without evidence of a dehiscence on conventional CT ⁵⁰, have been reported. CT images with higher spatial resolution will help clarify these disorders and whether patients with other dehiscences in otic capsule bone present differently than those with superior semicircular canal dehiscence syndrome.

Figure 2.

Examples of high resolution CT imaging of the right temporal bone in the same patient with slice thickness of 0.6 mm helical (A), 0.4 mm helical (B) and 0.1 mm flat panel (C). Upper panels show reconstructions in the plane of the superior semicircular canal and lower panels show reconstructions in the plane of the stapes. In these images the only pathology is a dehiscence over the tegmen tympani.

MRI of the inner ear has advanced with the combination of 3 Tesla clinical scanners, improved gradient technology and new pulse sequences. Gadolinium-based contrast agents (GBCA) have been found to be taken up in the perilymphatic space, and not the endolymphatic space ^51,52, with a delay of approximately 4 hours following intravenous administration of GBCA ⁵³ or 24 hours following transtympanic injection ⁵⁴. The differential uptake of gadolinium in the perilymph allows image contrast with the endolymph space, permitting assessments of the volume of endolymph. This has been helpful in studies of Ménière's disease, in which dilation of the endolymph space (i.e., endolymphatic hydrops) is common ⁵⁵. Thus far, the ability to see endolymphatic hydrops in vivo has revealed an association between the severity of endolymphatic hydrops and the severity of sensorineural hearing loss in patients with Ménière’s disease ⁵⁶. In patients with various disease states, some have observed enhancement earlier than expected or with greater signal intensity, leading to speculation that these observations reflect a leakiness of the blood-labyrinth barrier ⁵⁷. If GBCA were a marker of permeability of the blood-labyrinth barrier, these studies could improve understanding of inner ear pathophysiology. Improved gradient technology and higher strength static magnetic fields are likely to further increase spatial resolution, potentially allowing the diagnosis of a number of inner ear disorders that have been theoretical or identifiable only in postmortem specimens.

With increasing magnetic field strength, there is increased signal available for generating images with MRI, and there is interest in imaging the inner ear at 7 Tesla ⁵⁸. Dizziness and vertigo are also common symptoms when people are exposed to strong MRI machines ⁵⁹. Without visual fixation, all healthy humans tested thus far have nystagmus in strong MRI machines and the sensation of dizziness and velocity of nystagmus scales with increasing magnetic field strength ⁶⁰. The strong static magnetic field of an MRI machine interacts with the natural ionic currents entering the hair cells of the utricle, causing a force in the endolymph (i.e. a Lorentz force). This force displaces the cupulae of the superior and lateral semicircular canals, causing a sensation of vertigo and a persistent nystagmus the entire time someone is in a strong MRI machine ⁶¹. As stronger MRI machines become more widely available, this strange effect on the inner ear will need to be mitigated. This mechanism may be a useful way to stimulate the inner ear, and there is evidence that the brain is learning to adapt to the stimulus while in the MRI ⁶², suggesting a role for this effect in vestibular rehabilitation.

Restoring Vestibular Sensation with a Vestibular Implant

Important advancements have been made in the development and implementation of vestibular implants (VI). Four research groups are currently conducting human clinical trials studying the effects of electrical vestibular stimulation on vestibular reflexes and balance function in patients with bilateral vestibulopathy ^63–67. These devices sense head motion and deliver electrical stimulation via electrodes placed surgically in the ampullae of the semicircular canals. Different device designs have been used, including unmodified cochlear implants, combined vestibulo-cochlear implants, and dedicated vestibular implants. The targeted end-organ, implantation techniques, and inclusion criteria have varied across studies. The outcomes from these early studies are promising, with important findings including the relative safety of implantation compared to other surgeries of the inner ear, the ability to drive electrically evoked vestibular responses (motion perception, vestibulo-ocular reflexes, vestibulo-cervical reflexes, and vestibulo-spinal reflexes), improvements in assessments of balance and gait, and patient tolerance of device use both in an acute and chronic setting ^63–66.

While the existing collective experience supports great potential for this technology to provide relief to patients suffering from vestibular dysfunction, more work is needed to establish VI as a treatment. Recently, groups developing a VI published a joint statement about criteria for patient selection in future trials ⁶⁸. The authors recommended a stricter requirement for determining candidacy than the definition of bilateral vestibulopathy proposed by the ICVD ⁹, emphasizing the importance of defining severity of vestibular loss similar to assessments of auditory function. Similarly, electrophysiologic tests of the vestibular periphery would be helpful, and some evidence supports a vestibular microphonic similar to the cochlear microphonic that could be developed into an electrophysiological test ⁶⁹. As vestibular implants become incorporated into clinical practice, centers will need to develop resources to support implantation, electrode mapping, and vestibular rehabilitation.

Conclusions

While this review necessarily excludes unexpected developments, its aim is to highlight areas of current research that are likely to affect the diagnosis and management of the dizzy patient. Several diagnostic approaches are under development with immediate clinical applicability, as well as a technology in vestibular implants that is likely to transform the way otolaryngologists approach patients with dizziness.

Figure 1.

Perceptual threshold testing. A) Conventional rotatory chairs could be adapted for threshold testing, but with limited degrees of freedom. B) A 6-degrees of freedom motion platform allows stimuli in any directions of translation or rotation. C) Participants indicate the perceived direction of rotation for each stimulus and psychometric functions are fitted to determine a perceptual threshold. D) Thresholds can be measured for a variety of stimulus frequencies and plotted as a function of stimulus magnitude (amplitude, velocity or acceleration), similar to pure tone audiometry.

Key points.

• A common language for vestibular disorders and the symptoms they cause is being developed by the International Classification of Vestibular Disorders (ICVD) and will streamline communication, diagnosis, and progress in the understanding of vestibular disease.

• Virtual evaluation and management of patients with dizziness will continue, with new technology to remotely monitor eye movements. Ambulatory event monitoring of nystagmus will help clinicians diagnose patients with episodic dizziness.

• Similar to pure tone audiometry, perceptual threshold testing for vestibular sensation will become integrated into clinical practice at tertiary centers.

• Improved spatial resolution for both computed tomography (CT) and magnetic resonance imaging (MRI) will identify new vestibular disorders and help to understand better the pathophysiology of existing ones.

• Vestibular implants will enter clinical practice as a treatment for patients with bilateral vestibulopathy.