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Ménière’s Disease and Other Causes of Episodic Vertigo 

Ménière’s Disease and Other Causes of Episodic Vertigo

Chapter:
Ménière’s Disease and Other Causes of Episodic Vertigo
Author(s):

Yuri Agrawal

and Lloyd B. Minor

DOI:
10.1093/med/9780199608997.003.0022
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Introduction

Ménière’s syndrome is an inner ear disorder characterized by spontaneous attacks of vertigo, fluctuating low-frequency sensorineural hearing loss, aural fullness, and tinnitus. When the syndrome is idiopathic and cannot be attributed to any other cause (e.g. syphilis, immune-mediated inner ear disease, surgical trauma), it is referred to as Ménière’s disease (1). Ménière’s syndrome exhibits a relapsing–remitting pattern, with episodic attacks terminated by periods of restitution to normal auditory and vestibular function. Additionally, the natural history of Ménière’s syndrome is such that auditory and vestibular function typically decline over time (2).

Prosper Ménière first described this constellation of symptoms in 1861, and given the co-occurrence of auditory and vestibular phenomena he proposed that the pathological locus was the labyrinth (3). Subsequent investigations have corroborated his hypothesis: postmortem temporal bone analyses of individuals with Ménière’s syndrome demonstrated histopathological abnormalities in the labyrinth. Additionally, physiological tests of labyrinthine function were also found to be abnormal in these patients.

In this chapter we will review the clinical and pathophysiological features of Ménière’s disease that distinguish it from other disease processes in the differential diagnosis of vertigo and imbalance. We will begin by describing some key clinical characteristics of Ménière’s disease. We will then outline the central pathological hypothesis behind Ménière’s disease—endolymphatic hydrops—insofar as this informs our understanding of physiological and radiographic tests as well as management strategies in Ménière’s disease. We will explore the physiological effects of Ménière’s disease on vestibular function, as measured by caloric, head impulse, and vestibular-evoked myogenic potential (VEMP) testing. Finally, we will review management strategies for the treatment of Ménière’s disease.

Ménière’s disease: clinical features

The prevalence of Ménière’s disease has been reported to range from 3.5 per 100,000 persons in Japan,(4) 157 per 100,000 persons in the United Kingdom (5), 190 per 100,000 in the United States (6), to 513 per 100,000 in Finland (7). Disease onset typically occurs in the fourth to sixth decade of life, with a 1.3–1.9:1 female predominance (6, 8). Ménière’s disease tends to be unilateral and involves the contralateral ear in 30% of cases (9). The diagnosis of Ménière’s disease is largely clinical at this time; there are no pathognomonic tests that confirm this diagnosis. The most widely-used guidelines to establish a diagnosis of Ménière’s disease were published by the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), which termed ‘definite’ Ménière’s disease as two or more spontaneous episodes of vertigo each lasting 20 minutes or longer, hearing loss documented by audiograms on at least one occasion, tinnitus or aural fullness in the affected ear, and other causes excluded (typically with gadolinium-enhanced magnetic resonance imaging (MRI) of the cranial base) (10). The staging system established by the AAO-HNS is based on audiometric criteria, with four-frequency pure-tone averages at 0.5, 1, 2, and 3 kHz of <25, 26–40, 41–70 and >70 corresponding to Stages 1, 2, 3, and 4 respectively.

The presentation of Ménière’s disease typically includes recurring attacks of vertigo (96.2%), with tinnitus (91.1%) and ipsilateral hearing loss (87.7%) (11). The clinical course of Ménière’s disease varies considerably between patients, from long periods of remission punctuated by episodic attacks to intervals of unrelenting recurring attacks. Longitudinal studies suggest that vertigo ceases spontaneously in 57% of cases at 2 years and 71% after 8.3 years (12). Patients classically present with a low-frequency sensorineural hearing loss that is fluctuating and progressive. With long-standing disease (>10 years), the audiometric pattern flattens and the hearing loss stabilizes at a pure-tone average of 50 dB and a speech discrimination score of 50% (13). Profound sensorineural hearing loss occurs in 1–2% of patients (14); if the losses are bilateral patients may benefit from cochlear implantation. Interestingly, some patients with Ménière’s disease who undergo cochlear implantation continue to experience fluctuation in hearing in their implanted ear (15). Ménière’s disease has been shown to have significant adverse effects on quality of life, as measured by the Quality of Well-Being Scale (16). Poor physical and mental functioning scores as well as increased levels of depression were also noted in patients with Ménière’s disease (16).

Endolymphatic hydrops

Endolymphatic hydrops has long been held to be the pathological basis for Ménière’s disease (1719). Endolymph, the potassium-enriched fluid in the inner ear, may be either excessively synthesized or inadequately resorbed, resulting in expansion of the endolymphatic space (19, 20). Surgical ablation of the endolymphatic sac in experimental animals has reproduced the histopathological finding of endolymphatic hydrops seen in temporal bone specimens of individuals with Ménière’s disease, although these animals do not seem to experience the classic signs and symptoms associated with Ménière’s disease in humans (21, 22).

Endolymphatic hydrops typically involves the pars inferior of the labyrinth (comprising the saccule and cochlea) (18, 23). Saccular hydrops may range from mild to severe, based on the degree of membrane distension towards the stapes footplate (24). Cochlear hydrops is typified by bowing of Reissner’s membrane into the scala vestibuli; severity of cochlear hydrops also varies according to the degree of convexity towards the scalar wall of the modiolus (25). The pars superior (utricle and semicircular canals) may also be involved in endolymphatic hydrops, although changes tend to be less dramatic and occur less frequently.

Several mechanisms have been suggested to explain how endolymphatic hydrops may produce the spontaneous attacks of vertigo characteristic of Ménière’s disease. The most prominent theory holds that hydropic distension of the endolymphatic duct causes rupture of the distended membranes, a phenomenon that has been observed throughout the labyrinth (26). Membrane rupture allows the potassium-rich endolymph to leak into the perilymphatic space and contact the basal surface of the hair cells as well as the VIIIth cranial nerve. Initial excitation then subsequent inhibition of the hair cells manifests as a direction-changing nystagmus and may underlie the clinical phenotype of episodic vertigo.

Long-term declines in auditory and vestibular function may be the result of repeated exposure of the vestibular hair cells to toxic levels of potassium-enriched perilymph (27). The increased susceptibility of type II relative to type I hair cells in Ménière’s disease supports the hypothesis that chronic perilymph toxicity may cause neurosensory dysfunction (28). The vestibular neuroepithelium consists of type I and type II hair cells as well as supporting cells. Both hair cell types have cuticular plates and stereociliary bundles, reflecting their role in mechanosensory signal transduction. However, the two hair cell types can be distinguished basedon other morphological characteristics: type I hair cells are flask-shaped, have a round nucleus and are enveloped on their basal surface by an afferent nerve chalice. In contrast, type II hair cells are cylindrically-shaped, have oval nuclei, and small bouton-type nerve terminals from afferent and efferent nerve endings (29). The sparse nerve endings on the basal surface of type II hair cells may provide decreased protection against harmful ionic changes in the perilymph (28). The physiological and functional implications of the selective depletion of type II hair cells in Ménière’s disease are still poorly understood.

Alternatively it has been postulated that hydrops itself may occur in an episodic manner, as a result of sudden increases in the secretory function of the stria vascularis or of spontaneous obstruction of the endolymphatic sac (30). Hydropic distension may then cause a mechanical deflection of the macula and crista of the otoliths and semicircular canals respectively and thus vestibular hair cell depolarization, leading to the sensation of vertigo (30). Long-term changes to the neurosensory function of the vestibular apparatus may be the consequence of increased hydrodynamic pressure causing increased vascular resistance, compromised blood flow, and chronic ischaemic injury (31, 32).

Several lines of evidence challenge the primacy of endolymphatic hydrops in the pathophysiology of Ménière’s disease. As mentioned previously, experimentally-induced endolymphatic hydrops in animal models does not produce the clinical phenotype of Ménière’s disease in these animals. Moreover, a double-blind study of temporal bone specimens and associated clinical histories demonstrated that all individuals with Ménière’s syndrome diagnosed during life had evidence of endolymphatic hydrops on postmortem examination of their temporal bones; however, not all individuals with histopathological evidence of endolymphatic hydrops had clinical histories consistent with Ménière’s disease (33). If endolymphatic hydrops was central to the development of Ménière’s disease, one would expect the correlation between the clinical manifestations of Ménière’s disease and endolymphatic hydrops to be absolute.

Alternatively, studies are increasingly suggesting that endolymphatic hydrops may be a marker of some other pathological process that causes Ménière’s disease, such as disordered cochlear homeostasis (34). Emerging evidence implicates the fibrocytes of the spiral ligament which play a crucial role in maintaining cochlear fluid homeostasis: dysregulation of these cells appears to precede the development of hydrops (35). Genetic studies may generate additional insights into the pathological basis of Ménière’s disease. A familial genetic predisposition has been reported in 2–14% of cases (36), following an autosomal dominant inheritance pattern (37). Recent genome-wide association studies have identified polymorphisms in a potassium ion transporter and a protein also linked to hypertension in individuals with Ménière’s disease (38). Auto-immune mechanisms may also play a role, as evidenced by associations between specific human leukocyte antigens such as Cw7 and Ménière’s disease (39). This molecular genetic line of inquiry shows promise for yielding the true pathological basis for Ménière’s disease.

Based on endolymphatic hydrops as a presumed pathological correlate of Ménière’s disease, various electrophysiological and radiographic tests have been explored as providing supportive evidence for a diagnosis of Ménière’s disease. Electrocochleography measures electrical potentials generated by the cochlea in response to repeated sound stimulation. The cochlear response typically consists of a cochlear microphonic and summating potential (SP), both of which represent cochlear outer hair cell function, and the compound action potential (AP), which reflects auditory nerve activity and corresponds to wave I of the auditory brainstem reflex. The SP has been observed to be larger and more negative in patients with Ménière’s disease, leading to an elevated SP/AP ratio (>0.4). This is thought to reflect hydropic distension of the basilar membrane into the scala tympani causing an increase in the normal asymmetry of its vibration. The sensitivity of the SP/AP ratio has been reported to be 50–70% (40), and efforts to augment the sensitivity have included combining the SP/AP ratio with SP amplitude, AP latency, and audiometric parameters (41).

The pursuit of a diagnostic test for Ménière’s disease has also motivated research into imaging of endolymphatic hydrops. MRI scanning with the intravenous and intratympanic delivery of gadolinium has allowed for the visualization of the labyrinthine fluid spaces in vivo, and endolymphatic hydrops has been observed in many cases of clinically-diagnosed Ménière’s disease (42). As technological refinements continue to augment the power of MRI, the ability of MRI to resolve endolymphatic hydrops should concomitantly rise. It should be noted that studies of the predictive value of various tests for Ménière’s disease inherently suffer from the lack of an objective gold standard diagnosis for Ménière’s disease.

Caloric and head impulse testing in Ménière’s disease

Caloric and head impulse testing are both tests of semicircular canal function. In caloric testing, bithermal irrigation is applied to the external auditory canals, which causes a convective movement of endolymph within the ipsilateral horizontal semicircular canal (43). The movement of fluid within the horizontal canal results in excitatory or inhibitory deflection of the cupula (depending upon the direction of endolymph flow). Motion of the cupula then leads to hair-cell excitation or inhibition with a corresponding change in the discharge rate of vestibular-nerve afferents. Compensatory eye movements are thereby elicited (corresponding to the slow phases of nystagmus), followed by a rapid corrective saccades (corresponding to the fast phase of nystagmus). The maximum velocities of the slow phases of nystagmus are compared bilaterally and used to compute unilateral weakness or caloric asymmetry. A caloric asymmetry of 20% or greater is usually considered indicative of unilateral peripheral vestibular hypofunction.

Head impulse (or head thrust) testing assesses the integrity of the three-dimensional angular vestibulo-ocular reflex (AVOR). Head and eye movements are recorded during high-velocity, high-acceleration rotary head impulses in the plane excitatory for each of the six semicircular canals. Normal subjects are able to maintain visual fixation on a target during rapid head movement and thus have gain values (computed as the ratio of eye velocity to head velocity) close to 1.0 (44).

A significant reduction in the caloric response of affected ears has been observed in 42–79% of individuals with unilateral Ménière’s disease, and caloric asymmetries of 100% (i.e. absent caloric response in the affected ear) have been noted in 6–11% of patients (4551). In contrast, abnormalities of the AVOR in Ménière’s disease are much less prevalent. A study comparing caloric and head impulse testing in individuals with Ménière’s disease observed caloric testing abnormalities in 42% of subjects but AVOR abnormalities in only 13% of patients, although a significant linear correlation was noted between head impulse test gain asymmetry and caloric unilateral weakness percentage (Figure 22.1) (46).

Fig. 22.1 Head thrust test gain asymmetry (HTT GA) is plotted versus the caloric unilateral weakness (UW) in subjects with Ménière’s disease (filled triangles), and the regression line (solid line) fitting Ménière’s disease is also plotted. For comparison, data from Schmid-Priscoveanu et al. (85) for subjects with acute (open rectangles) and chronic (filled rectangles) vestibular neuritis (VN) are also plotted, along with the regression line (broken line) for both groups of VN subjects. Shaded regions indicate normal HTT GA (−5.8% to +5.8%) and normal caloric UW values (−20% to +20%). Figure reproduced with permission (46).

Fig. 22.1
Head thrust test gain asymmetry (HTT GA) is plotted versus the caloric unilateral weakness (UW) in subjects with Ménière’s disease (filled triangles), and the regression line (solid line) fitting Ménière’s disease is also plotted. For comparison, data from Schmid-Priscoveanu et al. (85) for subjects with acute (open rectangles) and chronic (filled rectangles) vestibular neuritis (VN) are also plotted, along with the regression line (broken line) for both groups of VN subjects. Shaded regions indicate normal HTT GA (−5.8% to +5.8%) and normal caloric UW values (−20% to +20%). Figure reproduced with permission (46).

The results of caloric and head impulse testing in Ménière’s disease are informative. First, although caloric testing is abnormal, the normal AVOR gains in Ménière’s disease suggest that there is substantial preservation of semicircular canal function in these patients (52). Additionally, although both caloric and head impulse testing are measures of semicircular canal function they appear to be capturing distinct phenomena. Caloric irrigation causes a slow convective flow of endolymph and provides a low-frequency stimulus to the vestibular system. In contrast, high-velocity rotary head thrusts cause rapid endolymph movement and generate a high-frequency input to vestibular afferents. It is possible that Ménière’s disease preferentially impairs the ability of the vestibular apparatus to process low-frequency signals. It should be noted that the low-frequency caloric stimulus is a non-physiological input, whereas the high-frequency head thrust approximates commonly-occurring stimulus frequencies to the vestibular apparatus. Thus it is also possible that mechanisms of central adaptation can only be established for physiological stimuli (leading to normal responses to head impulse testing) but not for inputs outside the normal range (i.e. caloric stimuli).

A similar dissociation between caloric and head impulse testing was observed in a study of semicircular canal function during acute attacks and quiescent periods (53). The authors found that in patients with early-stage unilateral Ménière’s disease, there was no asymmetry in caloric testing or AVOR gain during quiescent intervals. During acute vertigo attacks, these patients demonstrated ipsilateral caloric weakness and an increase in VOR gain with rotations towards the ipsilesional side (53). The hydropic ear may function as a high-pass filter: it dampens sensitivity to low-frequency stimulation and enhances sensitivity to high frequency stimulation.

VEMP testing in Ménière’s disease

Vestibular-evoked myogenic potentials are thought to reflect otolith function. The cervical VEMP (cVEMP) appears to be generated by a sacculocollic reflex. In the afferent limb of this reflex pathway, acoustically-sensitive cells in the saccule respond to brief, loud, monaural sound stimuli and transmit an electrical signal centrally via the inferior vestibular nerve. The efferent limb of this reflex arc sends an inhibitory impulse to the fibres of the ipsilateral sternocleidomastoid muscle; electromyographic recordings from this muscle in response to a sound input thus reflect saccular function (54, 55). Typical cVEMP testing paradigms elicit responses to broadband clicks and frequency-specific tonebursts. In normal subjects, click-evoked cVEMP responses can be elicited 98% of the time and short toneburst-evoked cVEMP responses occur 88% of the time (56).

Ocular VEMPs (oVEMP) are a newer vestibular-evoked potential to air-conducted sound or bone-conducted vibrational (BCV) stimuli. Responses are crossed and are excitatory to the contralateral inferior oblique muscle. One study found that the oVEMP in response to BCV is abolished in the setting of superior vestibular neuritis, suggesting that the vibration-evoked oVEMP may be a measure of utricular function (57). Studies of otolith function and Ménière’s disease have largely focused on the cVEMP; these studies will be reviewed in this section. More recent investigations into the diagnostic utility of the oVEMP will be discussed at the end of this section.

Individuals with normal saccular function exhibit frequency tuning of their cVEMP responses, such that sound thresholds required to elicit a cVEMP response are lowest when the sound stimuli are delivered at particular frequencies (58). The greatest sensitivity of the sacculocollic reflex appears to occur over the 200–1000-Hz frequency range (59, 60). Frequency tuning appears to be a function of both the testing apparatus as well as resonance properties of the saccule (which in part reflects the size of the saccule).

Given that Ménière’s disease is associated with cochleosaccular hydrops, and that cVEMP responses reflect saccular mechanics, it is logical that cVEMP testing would be altered in individuals with Ménière’s disease. Indeed, cVEMP responses to click stimuli were observed to be delayed or absent in 51–54% of patients with Ménière’s disease (61, 62) compared to the normal click-evoked response rates of 98% discussed previously. Additionally, cVEMP responses in individuals with Ménière’s disease exhibit altered frequency tuning, such that the greatest sensitivity of the sacculocollic reflex appears to occur at higher frequencies and across broader frequency ranges compared to normal subjects (Figure 22.2) (63). Changes in saccular resonance characteristics in the setting of hydrops are thought to underlie the abnormalities in cVEMP testing.

Fig. 22.2 Mean ± standard error of the mean vestibular-evoked myogenic potential thresholds for tone-burst and click stimuli in normal subjects’ ears (n = 14) and affected and unaffected ears of subjects with unilateral Ménière’s disease (n = 34). Figure reproduced with permission (63).

Fig. 22.2
Mean ± standard error of the mean vestibular-evoked myogenic potential thresholds for tone-burst and click stimuli in normal subjects’ ears (n = 14) and affected and unaffected ears of subjects with unilateral Ménière’s disease (n = 34). Figure reproduced with permission (63).

Further evidence that cVEMP responses are indicative of saccular dysfunction in Ménière’s disease comes from the observation of ‘dose–response’ relationships. Individuals with severe saccular dysfunction who experience drop attacks—otherwise known as otolithic crises of Tumarkin (64, 65)—have the greatest blunting and frequency shift of their cVEMP tuning curves (66). Additionally, 27% of individuals with unilateral Ménière’s disease were found to have cVEMP response abnormalities in their unaffected ear; the cVEMP tuning curves in these asymptomatic ears were noted to be intermediate in phenotype between affected and normal ears (67).

Cervical VEMP testing appears to be a powerful tool in the diagnosis of Ménière’s disease, likely because it specifically measures saccular function which is impaired in Ménière’s disease. Indeed, a study evaluating the relative ability of various vestibular physiologic tests to predict the side of lesion in individuals with unilateral Ménière’s disease found that cVEMP testing using a toneburst stimulus at 250 Hz correctly assigned the side of lesion in 80% of cases (68). This test performance was second only the 85% correct assignment seen with caloric testing where caloric asymmetry was defined as greater than 5% interaural difference (as opposed to the more conventional 20–30%). Another study evaluated differences in cVEMP thresholds between affected and unaffected ears in patients with unilateral Ménière’s disease as a measure of disease severity (69). The authors found a significant correlation between interaural cVEMP amplitude differences and Ménière’s disease stage based on AAO-HNS 1995 clinical criteria (69). Cervical VEMP testing shows particular promise as a measure of Ménière’s disease severity and in its ability to prognosticate bilateral disease.

Emerging evidence suggests that oVEMPs to air-conducted sounds demonstrate similar sensitivity to sound-evoked cVEMPs in the diagnosis of Ménière’s disease. Both the oVEMP and cVEMP in response to air-conducted sounds are thought to reflect saccular function, and in one study the sound-evoked oVEMP had a higher correlation with other measures of cochleovestibular function in Ménière’s disease—including caloric testing and hearing loss—than the sound-evoked cVEMP (70). Alterations in frequency tuning of the sound-evoked oVEMP in patients with Ménière’s disease have also been observed (71). Changes in otolith function during acute attacks and periods of remission have been explored using oVEMPs, and an increase in utricular function as measured by the vibration-evoked oVEMP and a decrease in saccular function as measured by the vibration-evoked cVEMP during acute attacks have been reported (72). The proliferation and specification of tests of otolith function will likely be of diagnostic utility and also shed light on the pathophysiology of Ménière’s disease.

Treatment

Given that the pathological basis of Ménière’s disease remains elusive, it follows that a curative treatment remains to be elucidated. Current therapies are directed at mitigating symptoms, particularly vertigo. First-line medical regimens include salt restriction and diuretics, aimed at alleviating endolymphatic hydrops. Betahistine, an H1-histamine receptor antagonist that increases inner ear blood flow, has been shown to reduce the frequency and severity of vertigo episodes. Betahistine is widely used in Europe in the treatment of Ménière’s disease although its use is limited in the United States given insufficient evidence for its efficacy (73). Increasing evidence is supporting the use of corticosteroids, particularly delivered intratympanically, in the treatment of Ménière’s disease. One large retrospective study found that control of vertigo symptoms was achieved in 91% of patients treated with intratympanic dexamethasone, allowing them to defer or avoid ablative therapies (74).

Medical therapy is insufficient to control vertigo symptoms in 10% of cases (75). Options for patients with refractory Ménière’s disease include surgical decompression of the endolymphatic system, and surgical or chemical ablation of vestibular function. In endolymphatic sac surgery, a transmastoid approach is used to decompress the sac with or without placement of a shunt to drain endolymph. Studies demonstrate positive outcomes from endolymphatic shunt surgery in terms of hearing preservation and vertigo control (76), although a recent meta-analysis found that there is insufficient evidence showing efficacy of this procedure relative to placebo (77). Selective vestibular neurectomy via middle fossa or posterior fossa approach has been shown to relieve vertigo symptoms in over 90% of cases, although potential complications of these procedures, including hearing loss, facial nerve weakness, cerebrospinal fluid leak, speech and language deficits (from temporal lobe retraction in the middle fossa approach), and headaches (from the posterior fossa approach) must be considered. Surgical labyrinthectomy achieves excellent vertigo control rates, although hearing in the operated ear is abolished. A new area of investigation involves the use of a vestibular neurostimulator in the treatment of Ménière’s disease. Using cochlear implant technology, an implantable device that delivers a fixed electrical signal during acute attacks to suppress the symptoms of vertigo has been tested in animal models and is being adapted for human use (78). The ongoing development of a multichannel vestibular prosthesis may also find use in patients with bilateral Ménière’s disease and bilateral vestibular hypofunction (79).

Surgical procedures are increasingly being supplanted by chemical ablation of the peripheral vestibular apparatus using intratympanic gentamicin. Gentamicin is a selective vestibulotoxic aminoglycoside antibiotic that is preferentially taken up by type I hair cells of the vestibular neuroepithelium (80). The use of low-dose intratympanic gentamicin has been shown to yield 70–90% vertigo control rates (81), and is associated with hearing loss in only 17% of cases (82). One study examined AVOR gain before and after intratympanic gentamicin administration (52). As noted previously, gain values in patients with Ménière’s disease were close to unity, although caloric responses were diminished in the majority of patients. Figure 22.3 depicts representative head (light grey dashed) and eye (dark grey and black) velocity traces for a 38-year-old woman with a 3-year history of episodic vertigo and right fluctuating sensorineural hearing loss and tinnitus before intratympanic gentamicin (52). Caloric testing showed a 23% right unilateral weakness. Each trace shows the patient’s head and eye velocities for head impulses that excited the indicated canal; ipsilateral impulses were directed toward the affected ear and contralateral impulses were in the direction of the intact ear. Figure 22.4 shows the head and eye velocity traces from the same woman obtained 49 days after a single intratympanic gentamicin injection to the right ear (52). She reported no further vertigo episodes after treatment. Her caloric testing revealed a 92% right unilateral caloric weakness, and her AVOR data showed marked reductions in the gain for rotations to the ipsilesional side.

Fig. 22.3 Responses to head impulse testing in a patient with Ménière’s disease measured before intratympanic gentamicin injection. Each panel shows head velocity (light grey dashed) and eye velocity (dark grey and black) for rotations in the excitatory direction for each canal. Data from 8–12 stimulus repetitions are shown for each canal. Head velocity has been inverted to permit a direct comparison of the stimulus and the response. The interval over which gain was analysed (30 ms prior to peak head velocity) is shown in black for each trace. The eye velocity before and after this analysis interval is shown in dark grey. A gain value was calculated as eye/head velocity for every point in time during the analysis interval. The response gain for each stimulus repetition was defined as the maximum gain value during the interval of analysis. The response gain (mean ± standard deviation for all stimulus repetitions) is given in each panel’s upper right corner. Figure reproduced with permission (52).

Fig. 22.3
Responses to head impulse testing in a patient with Ménière’s disease measured before intratympanic gentamicin injection. Each panel shows head velocity (light grey dashed) and eye velocity (dark grey and black) for rotations in the excitatory direction for each canal. Data from 8–12 stimulus repetitions are shown for each canal. Head velocity has been inverted to permit a direct comparison of the stimulus and the response. The interval over which gain was analysed (30 ms prior to peak head velocity) is shown in black for each trace. The eye velocity before and after this analysis interval is shown in dark grey. A gain value was calculated as eye/head velocity for every point in time during the analysis interval. The response gain for each stimulus repetition was defined as the maximum gain value during the interval of analysis. The response gain (mean ± standard deviation for all stimulus repetitions) is given in each panel’s upper right corner. Figure reproduced with permission (52).

Fig. 22.4 Responses to head thrusts that excited each of the six semicircular canals in a patient with Ménière’s disease (same as in Figure 22.1) measured 49 days after a single intratympanic injection of gentamicin. Panels, traces, and gain values are as described for Figure 22.1. Figure reproduced with permission (52).

Fig. 22.4
Responses to head thrusts that excited each of the six semicircular canals in a patient with Ménière’s disease (same as in Figure 22.1) measured 49 days after a single intratympanic injection of gentamicin. Panels, traces, and gain values are as described for Figure 22.1. Figure reproduced with permission (52).

Studies suggest that control of vertigo symptoms occurs with successful and enduring ablation of vestibular function: patients who sustained decreases in AVOR gain and increases in caloric weakness following intratympanic gentamicin were found to have fewer episodes of post-treatment vertigo and were less likely to require repeat therapy (83, 84). However, the correlation between the loss of semicircular canal function and symptom control is not absolute (84). It is possible that the natural history of Ménière’s disease—typified by a high spontaneous remission rate—may obscure an association between decreased vestibular function and relief from vertigo symptoms. Alternatively, recurrent vertigo may in part reflect otolith function which is not captured by caloric or head impulse testing.

Superior semicircular canal dehiscence syndrome and vestibular paroxysmia

Other vestibular disorders may present similarly to Ménière’sdisease and should be included in the differential diagnosis. Superior semicircular canal dehiscence syndrome (SCDS) and vestibular paroxysmia will be discussed here; the reader is referred to the following chapters for a discussion of vestibular migraine (Chapter 21), vascular etiologies (Chapter 23) and recurrent BPPV (Chapter 9). In 1998, Minor et al. described that dehiscence of bone overlying the superior semicircular canal can result in a clinical syndrome with symptoms and signs related to vestibular and auditory dysfunction.86 These patients mayexhibit a Tullio phenomenon (eye movements induced by loud noises) or Hennebert’s sign (eyemovements induced by pressure in the external auditory canal). Chronicdisequilibrium may also be present, and the auditory manifestations include autophony and pulsatile tinnitus.

The pathophysiology of superior canal dehiscence can be understood in terms of the effects of the dehiscence in creating a ‘third mobile window’ into the inner ear, thereby allowing the superior canal to respond to sound and pressure stimuli.86 The finding that eye movements evoked by sound or by pressure stimuli are in the same plane as the superior canal of the affected ear was important in focusing attention on the superior canal as the cause of these abnormalities.86,87 Typical physiologic findings in patients with SCDS include an air-bone gap on audiometry accompanied by supra-normalbone conduction thresholds (‘conductive hyperacusis’),88,89 and a lowered threshold for eliciting a cervical and ocular VEMP response in the affected ear.90,91 The diagnosis of SCDS is established with a high-resolution temporal bone CT scan showing a dehiscence of the bone overlying the superior canal (Figure 22.5).

Fig. 22.5 CT scan of a patient with bilateral superior canal dehiscences. Top panel is a coronal image, bottom panels are reformatted in the plane of the superior canals on the right (left panel) and left (right panel) sides.

Fig. 22.5
CT scan of a patient with bilateral superior canal dehiscences. Top panel is a coronal image, bottom panels are reformatted in the plane of the superior canals on the right (left panel) and left (right panel) sides.

Treatment in symptomatic patients includessurgical repair of SCD performed through the middle cranial fossa approach,86 although a transmastoid approach has also been described.92 The dehiscent superior canal is plugged with fascia and bone thereby obliterating the canal lumen, and the bony middle fossa plate is resurfaced with bone cement. Plugging the superior canal has been shown to result in resolution of symptoms, closure of the air-bone gap, and normalization of VEMP responses.93,94

Vestibular paroxysmia is a syndrome of episodic vertigo associated with neurovascular compression of the VIIIth cranial nerve, leading to nerve demyelination and ephaptic transmission of action potentials.95 A recent study established diagnostic criteria for definite and probable vestibular paroxysmia.96 Definite vestibular paroxysmia is characterized by: (a) at least five attacks of vertigo spells lasting seconds to minutes, (b) attacks associated with specificprovocative factors (e.g. head turn), and (c) attacks accompanied by tinnitus, hearing loss, aural fullness, or gait disturbance. Additionally, (d) certain objective criteria must be met, including neurovascular compression demonstrated on MRI (CISS sequence), hyperventilation-induced nystagmus as measured by electronystagmography (ENG), progression of vestibular deficit based on repeated ENG, or treatment response to antiepileptics. Moreover, (e) the symptoms cannot be explained by another disease. Probable vestibular paroxysmia has been defined as at least five attacks fulfilling criterion (a), and at least three of the criteria B–E.96 Treatment of vestibular paroxysmia typically includes antiepileptics(e.g. carbamazepine), and in selected symptomatic patients, microvascular decompression has been shown to be effective at reducing symptoms and improving quality of life in 80–85% of patients.97,98

Summary

Prosper Ménière first described the symptom complex of episodic vertigo, fluctuating hearing loss, aural fullness, and tinnitus 150 years ago. Despite the significant disability and diminished quality of life associated with this disease, a definitive understanding of the pathophysiological basis as well as curative treatment remain elusive. Fortunately, progress is being made on numerous fronts, specifically with respect to the molecular genetic basis of Ménière’s disease, enhanced imaging of endolymphatic hydrops, a heightened understanding of otolith dysfunction in Ménière’s disease, the increased use of otolith tests, and the development and refinement of therapeutics including intratympanic gentamicin and vestibular stimulators and prostheses. Hopefully definitive diagnosis and cure now lie within reach.

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