Visual Vestibular Mismatch

A poorly understood presentation of balance system disease

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Chapter 1

Preamble - Goals of the Thesis

Evaluation of patients with complaints of dizziness and imbalance has been recognized as extremely challenging since the time of Romberg (Romberg, 1846). Moritz Heinrich Romberg was a German neurologist who assessed patients by having them stand with their eyes closed to see whether they could maintain stability. Romberg was testing for tabes dorsalis, a form of tertiary syphilis where the posterior columns in the spinal cord are damaged, impairing proprioceptive information from the feet. He found that an affected patient was unable to maintain stability and would fall if he closed his eyes. Over the years it was realized that Romberg’s test was also positive in neurological disease other than syphilis, and it became part of the standard neurological assessment. It is insensitive at detecting acute vestibular disease (Longridge and Mallinson, 2010) and is also insensitive for detecting chronic unilateral vestibular impairment (Lanska and Goetz, 2000) but it is still in clinical use today. The sharpened Romberg developed in the 1960s (Graybiel and Fregly, 1966) is utilized clinically, and to this day has remained one of the only effective office assessments that can be used to screen for vestibular disease, although even its results can be confounded by a patient who has compensated, or even by age, which itself can be considered to be a “vestibular lesion” (Longridge and Mallinson, 2010).

Even to the present day, the assessment, diagnosis and treatment of the patient with dizziness is a challenging and often unrewarding task. As Matthews stated in 1963:

“There can be few physicians so dedicated to their art that they do not experience a slight decline in spirits when they learn that their patient’s complaint is dizziness. This frequently means that after exhaustive enquiry it will still not be entirely clear what it is that the patient feels wrong and even less so why he feels it.”

The purpose of this thesis is to address what in my opinion is a substantial shortcoming in our understanding, evaluation, assessment and clinical management of the patient with complaints of dizziness. So-called “traditional” complaints of dizziness that have long been recognized as being characteristic for balance system pathology (including spinning or similar sensations of movement) are often accompanied by nausea and imbalance. History taking in the patient with traditional complaints (even one presenting with a language barrier) is often a simple undertaking, and the symptom set in such patients is often easy to assess. Complaints of spinning (“vertigo” in North America) usually arise from the semicircular canals, and are indicative of pathology in these structures. There are standardly accepted evaluation techniques, such as videonystagmography and caloric testing. There are also management strategies such as particle repositioning maneuvres, Epley maneuvres, intratympanic gentamicin therapy, and vestibular rehabilitation therapy, and it is felt that the disease processes responsible for these complaints are reasonably well understood. This traditional aspect of vestibular disease will not be directly addressed in this thesis.

One of my main goals in this thesis is to address the patient with nontraditional complaints; these complaints are still probably of inner ear balance system origin. Our understanding of them is sadly lacking, and consists of clinical evidence supporting the known anatomical pathways and physiological function. Even more poorly understood is why there is such a wide range of symptomatic response to such deficits. This thesis also attempts to suggest reasons for this wide range. Some of these patients have an initial deficit, which can cause a minimal signal discrepancy, but this generates symptoms that can range from virtually unnoticeable, to quite bothersome, and in some extreme cases, totally debilitating. In my discussion, the extent to which these deficits are understood will be outlined and discussed.

A secondary goal of this thesis is to address the efforts that have been made to define these vague complaints. Controversies have arisen with regard to distinguishing different disorders (Bisdorff et al, 2009). A committee has been struck to explore this issue and classify these disorders, as it has been recognized recently that problems of terminology have arisen. One of the main focuses within this thesis has been to identify and characterize visual-vestibular symptoms. The committee unanimously thought it was important to develop a separate category for this symptom set. It has also been acknowledged that this symptom set arises from vestibular dysfunction, but this is not always well understood by practitioners outside of the vestibular community (Bisdorff et al, 2009). Terms such as ‚Äúvisual vertigo‚Äù have been used in the past, but have been suggested by the committee as being inappropriate, as these terms suggest a sensation of movement brought on by a visual stimulus. Although an agreement about nomenclature has not yet been agreed upon, it has been accepted that there is a set of symptoms that usually results from vestibular pathology, or the interplay between visual and vestibular systems (Bisdorff et al, 2009). This thesis will address patients’ symptoms by their characteristic names and suggest how they might fit in with the new nomenclature suggested by this committee.

Although techniques and strategies for diagnosing, assessing and managing non-traditional complaints of dizziness are limited, it has been recognized for 2000 years that these complaints are legitimate. A more recent breakthrough (see Yates et al, 1998) has detailed them anatomically and physiologically as a valid entity. This has allowed for the development of theories as to the physiology underlying the generation of these complaints. Historical development of our present understanding is important in arriving at an accurate diagnosis of these patients.

The body of this thesis consists of a series of nine peer reviewed published studies. I am the lead author on six of the studies, and the second author on the other three. All the studies were designed to validate the theories and advance our understanding of atypical vestibular complaints. The papers show that many patients having nontraditional complaints are suffering from balance system pathology and that this pathology can be secondary to neck trauma, head trauma or iatrogenic intervention, but can sometimes be idiopathic.

In the studies that form the body of this thesis, new criteria for documenting these non-traditional complaints are described. The criteria have also been related to those disturbances of the balance system that are understood more fully. For example, astronauts in space, and also after return to earth often experience unwell feelings of “space motion sickness” that are thought to be similar to motion sickness. These symptoms are generated as a result of balance system disturbance in microgravity (Oman et al 1986). Similar balance system disturbances can be induced by a “night on the town”. The hypothesis which this thesis evaluates is that partygoers, astronauts, and the patients with nontraditional balance system complaints have balance deficits which are sometimes temporary, sometimes persistent and possibly even permanent. Their symptoms are physiological rather than psychogenic or psychiatric and are recognized as arising from balance system deficits.

Chapter two is an introduction to my thesis and outlines the symptom set of visual vestibular mismatch (VVM), including historical perspectives. It includes an explanation of the symptom set, understanding of it through the ages, and our present day appreciation. It also examines why these patients are often difficult to diagnose, and how on occasion they have come to be erroneously categorized as psychiatric or neurotic.

Chapter three represents our “early work”. In this study, we identified a population of patients who had suffered whiplash type injury, but had not hit their head. Some of the patients had “standard” vestibular complaints and standard posturography findings suggestive of a vestibular deficit. However many of the patients voiced vague “atypical” complaints of lightheadedness and dislike of environmental movement. In these patients, the same standard posturography abnormalities were found, and we formulated the idea that perhaps their vague complaints were also of vestibular origin.

Chapter four describes further work that was carried out after we recognized that the vague complaints of our patients might represent peripheral vestibular disease. We encountered a group of patients with such complaints who had suffered whiplash injuries and/or minor head injury. We recognized that patients with “standard” vestibular syndromes had the same complaints as our whiplash patients, and the similarity of symptoms in the two groups led us to believe that the symptoms in both groups were caused by underlying vestibular disease.

Chapter five addresses suggestions that the symptom set of VVM might be arising from central pathology. Previous authors had looked at dizziness after whiplash injury, and had regarded these symptoms as suggesting brainstem and/or cerebellar injury related to the whiplash mechanism. We delineated two groups of whiplash patients with vestibular symptoms; those who had also suffered head injuries and those who had not suffered any head trauma at all. We saw the need to investigate the similarities and differences in these two groups, as we thought that the symptoms might be arising not from central pathology, but from peripheral vestibular injury caused by the mechanics of the whiplash trauma.

Chapter six looks at the development of VVM in patients with Ménière’s disease. It must be emphasized that it is not the purpose of this thesis to embark on an investigation or discussion of the clinical entity of Ménière’s disease. This chapter was a corollary of another study which investigated the efficacy of intratympanic gentamicin therapy (Longridge NS, Mallinson AI. Low-dose intratympanic gentamicin treatment for dizziness in Ménière’s disease. J Otolaryngol 2000 Feb;29(1):35-9). Some patients in that study developed symptoms of VVM after the therapy itself (i.e. creation of a iatrogenic peripheral vestibular lesion) and voiced symptoms similar to those reported by our whiplash patients, and by our “traditional” vestibular patients. Our corollary study looked at these patients.

Chapter seven looks at the evidence that we had gathered to date suggesting that VVM, visual vertigo and space motion sickness likely had a common origin, and probably reflected a “motion sickness”. Some people by their nature are motion sensitive, and we wondered if the development of these symptoms was due to a higher “autonomic sensitivity” or if motion sickness represented the upper end of caloric responses (i.e. vestibular sensitivity).

Chapter eight looks at the issue of age related decline in the vestibular system, as the clinical relevance of this to the development of VVM symptoms is unclear. The term “presbylibrium” has been used over the years by many authors (e.g. Furman and Cass (1996)) to refer to “disequilibrium of aging”. This term is still in use in the present day. Goebel (2008) outlined it as being caused by “structural and physiological deterioration in the sensory systems which maintain balance”. However this hypothesized deterioration is difficult to document. Furman and Redfern (2001) made the statement that the aging peripheral vestibular system remains functionally intact. They used off vertical axis rotation to show an age-related decline in otolith-ocular responses, but they hypothesized that this resulted from a decline in central vestibular processing, rather than from a loss of function of the otoliths themselves. We wondered if there was an age-related decline in caloric response (perhaps making older people more sensitive to the development of visual vestibular mismatch, as Paige (1992) had initially suggested).

Chapter nine examines symptoms of VVM after work related head injury. We had established that the development of VVM could occur after vestibular injury. We wondered if the symptoms in these patients were related to their head blow or were caused by peripheral vestibular injury.

Chapter ten looks at a subset of patients who had “atypical” Computerized Dynamic Posturography (CDP) results. The results in these patients suggested a nonspecific balance system deficit on all Sensory Organization Testing conditions, which were regarded in the literature as “aphysiologic” (Neurocom Equitest Data interpretation Manual, 1994; Furman, 1995). The literature suggested that these patients might have legitimate complaints, but the interpretation manual suggested (with no statistical support for the assumption) that vestibular system dysfunction was unlikely and these results were “suggestive of central nervous system pathology”. Many of these patients described vestibular symptoms and also had histories of newly developed VVM, and we thought that perhaps the non-specific CDP abnormality we saw in these patients might represent peripheral vestibular injury.

Chapter eleven looks at the effects of ethanol on gait. Many of our patients with VVM would characterize their complaints during history taking as “like I had had a little bit too much to drink”. We used a device which measures dynamic gait, to see if we could measure subtle balance deficits in subjects minimally impaired by ethanol. It has been suggested that the impairing effects of alcohol are related to reduced vestibular function (Tianwu et al, 1995), and that a sensitive method of measuring this deficit is using CDP conditions that exclude visual input (Ledin and Odkvist 1991). We thought it was important to try and show such subtle deficits, as perhaps these techniques could be transferred over to our patients with similar symptoms and signs.

Chapter twelve consists of a discussion of VVM and also details the historical development of our present understanding of the symptom set. In addition, it summarizes how the work in this thesis has helped to further our understanding of VVM. The discussion also examines the present, as well as the future direction of vestibular diagnostics, how our patients can be managed after they are finally supplied with an appropriate diagnosis, and how our understanding of the vestibular system, the autonomic nervous system, and the interaction between the two can better serve these patients. I will also try to incorporate the ideas advanced in this thesis into the new nomenclature that has recently been suggested and developed to standardize balance system disease (Bisdorff et al 2009). The hope is that this will help to reduce the confusion surrounding the symptom set of VVM.

There is a caveat to be kept in mind. The writer is aware that patients seen through our clinic are largely referred by otolaryngologists, and neurologists referring have either excluded neurological disease or wish to know the extent to which peripheral vestibular disease may be contributing to their patients’ complaints. We recognize that the complaints of VVM may arise as a result of neurological disease.

Chapter thirteen is a conclusion which presents ten relevant statements that must be kept in mind when trying to understand how complaints of VVM fit into the clinical picture in patients voicing these symptoms.