Equilibrium Research Vol. 76(2017) No. 4
AUGUST

　The concept of idiopathic sudden sensorineural hearing loss appeared after the term “Meniere's disease” was widely used. Until around the middle of the 20th century, sudden sensorineural hearing loss had been reported together with Meniere's disease. Moreover, sudden sensorineural hearing loss had been reported collectively regardless of the cause of the hearing loss. In 1944, de Kleyn reported a group of patients with sudden loss of function of the octavus-system in apparently normal persons. This was the first report in the literature which collectively described idiopathic sudden sensorineural hearing loss or idiopathic sudden deafness. From around the middle of the 20th Century, the number of papers regarding idiopathic sudden sensorineural hearing loss gradually increased. Vertigo occurred frequently in patients with severe hearing loss in the high-tone frequencies or with profound hearing loss throughout the whole range of frequencies. Recently magnetic resonance imaging revealed findings not only in the cochlea but also in the vestibule on the affected side in patients with vertigo. Endolymphatic hydrops was revealed in some patients with idiopathic sudden sensorineural hearing loss. These findings may contribute to the understanding of the etiology of sudden hearing loss including the vertigo mechanism. At the present time, however, the border between Meniere's disease and idiopathic sudden sensorineural hearing loss is unclear.

　We studied 121 patients who complained of dizziness or imbalance without nystagmus or other neurological symptoms. We divided these patients into four groups according to the initial diagnosis made at first visit. There were 30 patients with dizziness associated with headache (migraine or tension-type headache), 24 with imbalance caused by autonomic dysfunction, 39 with psychogenic dizziness, and 28 patients with unknown cause of dizziness. The patients were treated according to the initial diagnosis and their symptoms were observed. Some patients underwent vestibular testing using electro nystagmo graphy (ENG) to detect central vertigo or canal paresis. Brain magnetic resonance imaging (MRI) or computed tomography (CT) were performed for some patients with suspected central vertigo. Subsequently, 14 patients were diagnosed with central vertigo and another 14 patients with vestibular disease. Only two of 14 patients with central vertigo showed abnormal findings on MRI, however, all of them showed abnormal eye movements on ENG. Finally, we diagnosed 27 patients with dizziness associated with headache, 18 with autonomic dysfunction, and 32 with psychogenic dizziness. Sixteen cases were still with unknown causes. We administered preventive medicine or kampo for the headache on dizzy patients with associated headache and also monitoring of a diary for headache and dizziness. Most patients with dizziness associated with either headache or autonomic dysfunction have become better within 1 year. Some patients with psychogenic dizziness dropped out from our treatment, while others continued the long term treatment.

　Over a 2-year period from 2013 to 2014, we performed a clinical study at our center of 1,068 patients with a chief complaint of dizziness/equilibrium disorder. The ratio of males to females was 2: 3, with the highest proportion of men in their 60s. The distribution of females was bimodal, with the highest proportions of females in their 40s, 60s, and 70s. The majority of referrals were directly received at our department, but the next most was introductions from otolaryngology practitioners. Peripheral vestibular disorder accounted for approximately 77% of all cases, among which BPPV, Ménière's disease, and vestibular neuritis were observed in ascending order. Cerebrovascular accidents were observed in approximately 9% of all cases. We demonstrate the importance of the use of diagnostic criteria during examinations for dizziness. A higher proportion of referred cases had BPPV and Ménière's disease and many referrals were from otolaryngology practitioners, which suggest that refractory cases are also included in the preset study population. The utility of nystagmus examination in the emergency room and during consultations may improve diagnostic accuracy in such cases. Although undiagnosed cases are included in any clinical study, we believe further improvements in diagnostic techniques will have greater utility than the use of follow-up for diagnostic confirmation.

　The superior semicircular canal dehiscence syndrome (SCDS), which presents with comprehensive symptoms such as hyperacusis, autophony, and pressure-induced vertigo, has been recently recognized in Japan. Three patients with SCDS, in whom severe vestibular symptoms were unable to be controlled with conservative treatments, underwent capping surgery through the middle fossa approach. The preoperatively air-bone gap (AB gap) in the audiometry, the decreased threshold of cervical vestibular evoked myogenic potentials (cVEMP) and bone dehiscence of the superior semicircular canal could be observed in all patients on CT imaging. All patients suffered from positional vertigo for about one week after the operation. However, their cochlear and vestibular symptoms associated with the SCDS were relieved within a few months after the operation. The capping procedure decreased the AB gaps and increased the thresholds of cVEMP in all patients. We suggest that capping surgery via the middle fossa approach for the SCDS is an efficient procedure without severe side effects.

　[Introduction] Nystagmus associated with benign paroxysmal positional vertigo (BPPV) canalolithiasis gradually decreases with repeated positional change (fatigability). In other examples, the nystagmus disappears suddenly with positional change and appears again, the mechanism behind which would appear to be different from fatigability. We suspect this phenomenon is being induced by otoconia attached to and detached from the base of the crista. We have arbitrarily called this “cristolithiasis.” The validity of this theory was investigated.

　[Method] The bullfrog labyrinth was used as a model. The membranous labyrinth was cut at the crus commune to create a tiny opening. A small piece of otoconia, removed from the sacculus of the other ear, was introduced through this opening into the canal lumen. Experiment 1: The position of the preparation was changed so that the otoconia move back and forth within canal to canal and canal to ampulla. We observed the movement of the otoconia for maximum up to ten times. The rates of otoconia attachment to the canal wall and the crista were investigated. Experiment 2: The model of the otoconia attached to the cupula (cupulolithiasis) or the crista (cristolithiasis) was used. These models were given two kinds of stimuli, a. gravity and b. vibration. Experiment 2a (Gravity): The labyrinth preparation was placed so that the cupula-to-crista axis was in the horizontal plane with the canal side in downward position for 30 minutes. The rates of the otoconia detachment from the crista or the cupula were investigated. Experiment 2b (Vibration): Mechanical vibration was applied to the bony labyrinthine capsule of these models using a surgical drill. The time required for otoconial detachment was measured.

　[Result] Experiment 1: No otoconial mass was attached to the canal wall in 6 labyrinth preparations. The otoconial mass was attached to the crista in 5 out of 6 (83.3%). The otoconia were attached more easily to the crista than the canal wall. Experiment 2a (Gravity): In cupulolithiasis models, the otoconial mass was detached within 30 minutes in 2 out of 10 (20%) labyrinth preparations. In cristolithiasis models, the otoconial mass was detached within 30 minutes in 11 out of 14 (78.6%), which was significantly higher than in the cupulolithiasis models (p=0.015). Experiment 2b (Vibration): In the cupulolithiasis models (n=14), the average detachment time was 140.3 seconds. In the cristolithiasis models (n=11), the average detachment time was 25.5 seconds, which was significantly shorter than in the cupulolithiasis models (p=0.0010). The otoconia associated with cristolithiasis were detached more easily than in the case of cupulolithiasis.

　[Discussion] The inner wall of the semicircular canal is covered by cells with a smooth surface. In canalolithiasis, the otoconia move along the canal smoothly. On the other hand, the basal portion of the wall near the crista has transitional cells, planum semilunatum, and dark cells. The epithelia have microvilli and secretory activity to which the otoconia easily become attached. The attachment is weaker than in cupulolithiasis. It is assumed that this attachment and detachment of the otoconia near the crista lead to disappearance and return of the nystagmus.

　Benign paroxysmal positional vertigo (BPPV) is the most common peripheral vertigo and is characterized by brief attacks of rotatory vertigo associated with positional and/or positioning nystagmus, which are elicited by specific head positions or changes in head position relative to gravity. The pathophysiology of BPPV is canalolithiasis comprising free-floating otoconial debris within the endolymph of a semicircular canal, or cupulolithiasis comprising otoconial debris adherent to the cupula. In the canalolithiasis theory, when patients with BPPV move their head, free-floating otoconial debris in the canal creates the endolymph flow, the flow of the fluid causes deflection of the cupula of the canal, and as a result, the canal is stimulated or inhibited and nystagmus and vertigo are induced. In the cupulolithiasis theory, when patients with BPPV move their head, the cupula, with its adherent otoconial debris, deviates in the direction of gravity, and as a result, the canal is stimulated or inhibited and nystagmus and vertigo are induced.

　 In this review, we provide the classification, diagnostic criteria for BPPV published by the Japan Society for Equilibrium Research and the Bárány Society. The diagnostic criteria for BPPV published by the Bárány Society are part of the International Classification of Vestibular Disorders (ICVD)-an endeavor for classification of vestibular disorders steered by the Committee for Classification of Vestibular Disorders of the Bárány Society. In the two diagnostic criteria, canalolithiasis of the posterior canal, canalolithiasis of the lateral canal, and cupulolithiasis of the lateral canal have been accepted as BPPV, but the other variants of BPPV, such as canalolithiasis of the anterior canal, cupulolithiasis of the posterior canal, lithiasis of multiple canals, etc., have been classified into emerging and controversial syndromes or an atypical type.

　In this symposium, we have discussed the diagnostic criteria of Ménière's disease including the newly published one from the Japan Society for Equilibrium Research (JSER) in 2016.

　The diagnosis of Ménière's disease is primarily based on the clinical symptoms of vertigo attacks and hearing loss, which usually fluctuates. Historically, several different diagnostic criteria have been published by: 1) The Japanese Ménière's disease study group in 1974 and 2008; 2) The JSER in 1987 and 2016; and 3) The American Academy of Otolaryngology-Head and Neck Surgery in 1995. 4) The Bárány Society also proposed diagnostic criteria for Ménière's disease in 2015. In order to address the future direction for the diagnosis, treatment and research of Ménière's disease, it is crucial to comprehensively understand how these criteria describe the symptoms and background etiology of Ménière's disease. For example, the exact definitions of the term “vertigo” differ among these criteria. In the Japanese criteria, “vertigo” is not restricted to a rotating sensation of the body, whereas the American criteria define “vertigo” as a spinning sensation. In the Japanese criteria, hearing loss temporally coincides with the vertigo attacks, whereas the American and Bárány Society's criteria do not have such restrictions. Along with the current advances in diagnostic tests for otologic diseases, the Bárány Society's criteria include an updated list of the differential diagnosis for Ménière's disease. Most importantly, the Japanese criteria and the American criteria strongly support the hypothesis that the etiology of Ménière's disease is endolymphatic hydrops, and the Japan Society's 2016 criteria include MRI identification of hydrops. In the Bárány Society's criteria, the pathogenesis includes not only endolymphatic hydrops but other conditions as well. It is important to understand the concordance and differences of these criteria for the diagnosis of Ménière's disease.

　The authors introduced the diagnostic criteria recently revised by the Japan Society for Equilibrium Research. In addition, several issues related to diagnosis of vestibular neuritis were discussed. Firstly, partial involvement of the vestibular nerve was discussed. Conventionally, in order to prove peripheral vestibular disorders, caloric tests have been used. However, caloric tests cannot clarify disorders of the inferior vestibular nerve with preservation of the superior vestibular nerve function. If inferior vestibular neuritis is recognized as a kind of vestibular neuritis, the diagnostic criteria need further revision. Additionally, the head impulse test should be considered as a new diagnostic tool for vestibular neuritis. Secondly, the authors stated that “vestibular neuritis” could include vestibular neurolabyrinthitis and vestibular labyrinthitis in addition to vestibular neuritis as the current diagnostic criteria do not require differentiation of retro-labyrinthine lesions from labyrinthine lesions. Thirdly, the number of vertigo attack was discussed. Vertigo associated with vestibular neuritis should not strictly occur as a single episode, but rather as several attacks. Finally, the authors stated that “vestibular neuritis” should be changed to another term in order to express its actual states.

　The Behavioral Subcommittee of the Committee for the Classification of Vestibular Disorders of the Bárány Society defined the following seven conditions that are related to psychiatric disorders with vestibular symptoms: Episodic vestibular syndrome due to anxiety; chronic vestibular syndrome due to anxiety; anxiety complicating vestibular syndrome; vestibular symptoms due to depression; depression complicating a vestibular syndrome; vestibular illness anxiety; and fear of falling. Basically, anxiety and depression are the two major psychiatric disorders that could be associated with vestibular symptoms. They could be the primary or secondary psychiatric disorders that cause or amplify vestibular morbidity. Vestibular symptoms may be acute, episodic, or chronic. Vestibular illness anxiety is a category of somatoform disorders rather than anxiety and depression. Fear of falling is categorized as a phobia. In addition, persistent postural perceptual dizziness (PPPD) was defined as an interface of vestibular and psychiatric disorders that is characterized by chronic dizziness exacerbated by upright posture, active or passive movement and visual stimuli.