Otology & Neurotology 35:1626Y1632 Ó 2014, Otology & Neurotology, Inc.
Sudden Sensorineural Hearing Loss With Simultaneous Positional Vertigo Showing Persistent Geotropic Direction-Changing Positional Nystagmus *Chang-Hee Kim, *Jee Min Choi, *Hyo Vin Jung, †Hong Ju Park, and *Jung Eun Shin *Department of OtorhinolaryngologyYHead and Neck Surgery, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea; and ÞAsan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
Objectives: To characterize the clinical features of patients who simultaneously developed ipsilateral sudden sensorineural hearing loss (SSNHL) and positional vertigo showing geotropic directionchanging positional nystagmus (DCPN) on a supine head-roll test, and to address the possible pathophysiology of the disease. Study Design: Retrospective case series review. Methods: We conducted a retrospective case series study in 17 patients with SSNHL and simultaneous positional vertigo showing geotropic DCPN. Results: All 17 patients showed persistent geotropic DCPN without latency in the supine head-roll test. The intensity of nystagmus was stronger when the patient’s head was turned to the lesion side of SSNHL in 15 of 17 patients. We sought to identify a null plane in
nine patients, and the null plane was identified on the same side as the SSNHL in all nine patients, which was thought to be caused by the ‘‘light cupula’’ of the lateral semicircular canal in the same ear as the SSNHL. Conclusion: A light cupula mechanism may be one of the causes of positional vertigo in patients with SSNHL. In these cases, persistent geotropic DCPN is observed in the supine head-roll test and the null plane can be identified on the same side as the hearing loss. Key Words: Benign paroxysmal positional vertigoVHeadroll testVPersistent geotropic direction-changing positional nystagmusVPositional vertigoVSudden sensorineural hearing loss. Otol Neurotol 35:1626Y1632, 2014.
Sudden sensorineural hearing loss (SSNHL) is characterized by sensorineural hearing loss of at least 30 dB in three contiguous audiometric frequencies occurring over 3 days or less (1). Although the etiology of SSNHL is still idiopathic, viral infection, labyrinthine ischemia, labyrinthine hemorrhage, and disruption of the cochlear membrane are believed to account for most of the pathophysiology (2). Considering that the lesion site lies within the inner ear organs (2), which are interconnected through the endolymph and surrounding membranes, disturbances of both cochlear and vestibular function may occur simultaneously. Benign paroxysmal positional vertigo (BPPV), which is characterized by a brief episode of rotatory vertigo and nystagmus elicited by a change in head position, can be
simultaneously accompanied by SSNHL in 5 to 19% of all SSNHL patients (3Y6). While the posterior semicircular canal (PSCC) was the most commonly involved canal in some reports (3), the lateral semicircular canal (LSCC) was the most commonly involved canal in others (4,5). In terms of hearing recovery, the presence of BPPV was a poor prognostic factor in some reports (3,6), whereas it was not a prognostic factor in other reports (4,5). Compared with idiopathic BPPV, BPPV with SSNHL required a larger number of canalith repositioning procedures (CRPs) for successful treatment, and consequently showed longer disease durations (3). Thus, clinical features are different between idiopathic BPPV and secondary BPPV associated with SSNHL, which may raise the possibility that the pathophysiology of positional vertigo may differ. Previous reports on simultaneous BPPV with SSNHL suggested that selective damage to the cochlea and the utricle may be the causes of the specific clinical findings (7,8). Viral neurolabyrinthitis instead of labyrinthine infarction was thought to be more compatible with this ‘‘patchy’’ loss of inner ear function.
Address correspondence and reprint requests to Chang-Hee Kim, M.D., Ph.D., Department of OtorhinolaryngologyYHead and Neck Surgery, Konkuk University Medical Center, Konkuk University School of Medicine, 120-1 Neungdong-ro (Hwayang-dong), Gwangjin-gu, Seoul, Korea 143-729; E-mail: [email protected] The authors disclose no conflicts of interest. Supplemental digital content is available in the text.
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SSNHL WITH PERSISTENT GEOTROPIC DCPN Direction-changing positional nystagmus (DCPN) is typically observed in patients with LSCC BPPV when the patient’s head is turned to either side in the supine position (the supine head-roll test). In canalolithiasis-type LSCC BPPV, DCPN beats toward the lowermost ear (geotropic), which is transient with a latency of a few seconds, and weakens after repetitive examination (demonstrates fatigability). Recently, the concept of a ‘‘light cupula’’ in the LSCC that shows persistent geotropic DCPN has been introduced (9Y12). Previously, patients with SSNHL and simultaneous positional vertigo showing geotropic DCPN in the supine head-roll test have been reported (7,13), and the characteristics of geotropic DCPN were as follows: (1) the duration of nystagmus was prolonged, (2) the intensity was stronger upon turning the head towards the side of hearing loss, and (3) the nystagmus did not fatigue on repeated testing. In the present study, we report 17 patients with ipsilateral SSNHL and simultaneous positional vertigo showing persistent geotropic DCPN. Clinical characteristics are described, and a possible mechanism of this condition is discussed. SUBJECTS AND METHODS Subjects We evaluated 17 patients (nine men and eight women; mean age, 49 yr; range, 22Y72 yr) with ipsilateral SSNHL and simultaneous BPPV showing geotropic DCPN between June 2006 and September 2013. All patients met the clinical diagnostic criteria for SSNHL, which is defined as sensorineural hearing loss of 30 dB or more over at least three contiguous frequencies developing within 3 days. Determination of the hearing level in the affected ear was based on the opposite healthy ear. The vertigo attack occurred almost simultaneously with the onset of hearing loss (within 24 h). The study was approved by the Institutional Review Board (KUH1110032). The medical history of each patient was thoroughly investigated, and a neuro-otological examination was performed. Otoscopic examination revealed normal tympanic membrane without any evidence of acute or chronic otitis media in all patients. They denied recent head trauma or surgery, and did not complain of meningitis symptoms such as headache and neck stiffness. Neurological examinations revealed no abnormality in any of the patients. All 17 patients took brain MRI, which did not reveal acute infarction or other acute brain lesions in any of the patients. None of the patients reported taking medicines that may influence vestibular function, including vestibular suppressants, at least 24 hours before the examination. All patients were administered systemic high-dose steroids (prednisolone 1 mg/kg/d for 4 d, and then tapered off during the subsequent 10 d). Some patients subsequently received an intratympanic steroid injection as a salvage treatment.
Audiometry The pure-tone average (PTA) was measured as the average threshold at 500, 1,000, 2,000, and 3,000 Hz. Audiograms were categorized as high-tone, low-tone, flat type, or profound hearing loss. When a patient’s audiogram showed an average loss of 4 to 8 kHz from an average of 0.25 to 0.5 kHz by 30 dB or more, the type of hearing loss was classified as ‘‘high-tone hearing loss.’’ The ‘‘low-tone hearing loss’’ group demonstrated an average loss
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of 0.25 to 0.5 kHz, surpassing the average of 4 to 8 kHz by 30 dB or more. The ‘‘flat-type’’ group consisted of patients with a difference of 20 dB or less between the worst and best hearing levels at six frequencies (0.25, 0.5, 1, 2, 4, and 8 kHz). In the group with profound hearing loss, at least two frequencies produced results that were off the scale, and the difference between the hearing level and maximum sound level generated by the audiometer was within 10 dB at all six frequencies (14). The final PTA was recorded at 3 months after treatment, and hearing recovery was assessed according to the Siegel classification system (15).
Examination of Positional Nystagmus and Vestibular Function Tests The patient’s eye movement was examined at various head positions using Frenzel glasses or goggles installed with an infrared camera (SLMED, Seoul, Korea) by otolaryngologists at the clinic. Then horizontal nystagmus was documented using a videobased system in some patients (CHARTR VNG; ICS Medical, Schaumburg, IL) to calculate the slow-phase velocity (SPV) of nystagmus. All 17 patients underwent the following positioning sequence: (1) the patient lies down in the supine position, (2) the patient’s head is turned to the right over 90 degrees in the supine position, and (3) the patient’s head is turned to the left over 90 degrees in the supine position. Heads were turned to the right or left over about 20 degrees (15Y25 degrees) in the supine position to find the null plane in nine patients. Nystagmus was examined for at least 2 minutes at each position, and the head movement was paused for more than 1 minute in the supine position without any neck rotation between the positioning maneuvers. A bithermal caloric test was performed while recording eye movements using an infrared video-based system. Each ear was irrigated with a constant flow of water at alternating temperatures of 30-C and 44-C for a constant period of time (30 s). The maximum slow-phase velocity (mSPV) of nystagmus was calculated after each irrigation, and Jongkees’ formula was used to determine canal paresis (CP). A CP 25% or greater was considered abnormal. The method of evaluation of the static subjective visual vertical (SVV) was described previously (14). Briefly, in the dark, a dim white line was displayed on a computer monitor, which was placed 100 cm away from the patient. The line was 3 mm wide and 230 mm long, and a dot (3 mm in diameter) was superimposed on the line along the center of the line’s rotational axis. The patients were seated upright on a chair, and their heads were stabilized using a neck rest. The subjects were asked to adjust the visual rod to the vertical position by manipulating a remote controller held in both hands. During each test, the line was offset approximately 10 to 40 degrees clockwise or counterclockwise in a random order. When the line appeared vertical, the subject was instructed to click an enter button, which would automatically calculate the deviation in degrees from the true gravitational vertical. The mean of five tests was used as a measure of SVV tilt, and we considered this value to be abnormal if the tilt was 2.7 degrees or greater (14).
RESULTS Audiologic Characteristics of SSNHL Patients With Positional Vertigo Showing Persistent Geotropic DCPN All patients complained of ipsilateral sudden hearing loss and positional vertigo. Vertigo developed after the onset Otology & Neurotology, Vol. 35, No. 9, 2014
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R R R R R R R L R R R L R L L R R
115 85 92.5 57.5 95 115 115 92.5 56.3 115 61.3 115 115 113.8 48.8 115 110
0 0 0 32 0 0 0 0 36 0 80 0 0 0 80 0 0
Profound Flat-type Flat-type High-tone High-tone Profound Profound Flat-type High-tone Profound Flat-type Profound Profound Profound High-tone Profound Profound
Type of HL 111 88.8 86.3 15 61.3 113 78.8 36.3 43.8 115 30 88.8 96.3 103 27.5 115 91.3
0 0 0 92 44 0 0 76 48 0 92 8 0 0 96 0 0
G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24
Final Final Period from PTA (dB) SDS (%) HL to V (h) Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent
geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN
HR Y (10:10) R (89:16) R (8:5) Y (17:17) R (41:36) R (8:6) R (28:16) L (4:2) R (15:8) R (24:15) R (15:8) L (41:36) R (108:49) L (5:15) L (12:20) R (40:18) R (21:16)
LB (2) LB (7) LB (3) LB (6) LB (11) LB (2) LB (4) RB (1) LB (4) LB (5) LB (4) RB (2) LB (14) RB (4) RB (7) LB (5) LB (5)
NT NT NT NT NT NT NT NT R R R L R L L R R
Strong Supine side on HR (SPV, degrees Side of (SPV, R:L) per second) null plane
Positional nystagmus
Summary of clinical characteristics and test results of the patients (n = 17)
L4.7 Normalb Normal Normal Normal L2.9 Normal Normal Normal R3.6 Normal Normal Normal R3.4 Normal Normal L3.7
Caloric CP (%) Normala Normal R29 R58 R35 L36 Normal L30 Normal R68 Normal Normal R25 L75 L47 R96 R51
5 6 7 5 8 6 5 7 7 3 3 5 5 6 2 6 4
Symptom duration of SVV positional (degrees) vertigo (d)
‘‘R’’ or ‘‘L’’ before the SVV values indicate that the subjective visual vertical was tilted to the patient’s right or left side, respectively. ‘‘R’’ or ‘‘L’’ before the caloric CP values indicate that canal paresis was observed on the patient’s right or left side, respectively. SSNHL indicates sudden sensorineural hearing loss; PTA, pure-tone average; SDS, speech discrimination score; HL, hearing loss; V, vertigo; HR, supine head-roll test; SPV, maximal slow phase velocity (degrees per second); CP, canal paresis; SVV, static subjective visual vertical; L, left; R, right; DCPN, direction-changing positional nystagmus; RB, right-beating; LB, left-beating; NT, not tested. a A CP of less than 25% was considered normal. b A SVV of less than 2.7 degrees was considered normal.
1/M/72 2/F/68 3/M/61 4/M/48 5/F/52 6/F/64 7/F/22 8/M/40 9/M/39 10/F/56 11/M/55 12/F/51 13/F/40 14/M/52 15/F/50 16/M/67 17/M/25
Patient Initial Initial no./sex/age (yr) Side PTA (dB) SDS (%)
SSNHL
TABLE 1.
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Otology & Neurotology, Vol. 35, No. 9, 2014
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SSNHL WITH PERSISTENT GEOTROPIC DCPN of sudden hearing loss in all 17 patients. The positional nystagmus results and clinical characteristics are shown in Table 1. The male-to-female ratio was 9:8. Among the 17 patients, profound hearing loss was the most common type of hearing loss, and was observed in 9 patients (53%), which was consistent with previous observation (5). Both flat-type and high-tone hearing loss were observed in four patients (24%), each. None of the patients exhibited low-tone hearing loss. The initial PTA
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was 93.2 T 28.7 dB (n = 17), and mean speech discrimination score was 13.4 T 27.5%. Three months after treatment, the mean hearing threshold was 76.5 T 33.9 dB (n = 17), which was significantly different from the initial hearing threshold ( p = 0.001, paired t test). The improvement in the hearing threshold was 18.6 T 17.1 dB (n = 17). The hearing recovery rates were classified as complete recovery (n = 1), partial recovery (n = 3), slight recovery (n = 5), or no recovery (n = 8)
FIG. 1. SSNHL on the left side and simultaneous positional vertigo with persistent geotropic DCPN. In the upper panels, the left LSCC and the patient’s head viewed from the top of the patient’s head are depicted. In the lower panels, the video-nystagmographic findings of patient 14 are shown, who exhibited positional nystagmus compatible with a light cupula of the left LSCC. In supine position (A), right-beating nystagmus (maximal SPV = 4 degrees per second) was persistently observed due to utriculofugal deflection of the cupula. B, When the head was slightly turned (20 degrees) to the left side, the nystagmus disappeared (only artifacts from the patient’s eye blinking are shown). In this null plane, the cupula is aligned within the plane of the gravitational vector. C, When the head was turned to the left in the supine position, left LSCC was activated because of utriculopetal deflection of the cupula, and geotropic nystagmus (maximal SPV = 15 degrees per second) was observed. Note that the directions of nystagmus in the supine position and in left head-rolling are opposite to each other. D, The cupula of the left LSCC was deflected utriculofugally when the head was turned to the right side in the supine position, which caused geotropic nystagmus (maximal SPV = 5 degrees per second). Note that the intensity of nystagmus is stronger in left head-rolling than in right head-rolling. SSNHL, sudden sensorineural hearing loss; DCPN, direction-changing positional nystagmus; LSCC, lateral semicircular canal; SPV, slow-phase velocity. Otology & Neurotology, Vol. 35, No. 9, 2014
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according to Siegel’s criteria. Mean speech discrimination score was 26.8 T 38.7% after treatment. Characteristics of Positional Nystagmus In the supine head-roll test, geotropic DCPN with prolonged duration was observed in all patients (Fig. 1C and D, Supplementary videos 1 and 2, http://links.lww.com/MAO/A227 and http://links.lww.com/MAO/A228). We compared the mSPV of nystagmus on head-turning to the right with that to the left, and a stronger side was recognized in 15 of 17 patients (88%), and was on the same side as the SSNHL (Table 1). In the supine position, all 17 patients showed persistent nystagmus beating in the opposite direction of the SSNHL (Table 1, Fig. 1A, Supplementary video 3, http://links.lww.com/MAO/A229). Recently, the concept of a ‘‘light cupula’’ of the LSCC has been introduced (9Y12), even though the pathophysiology is still not clear. The diagnostic criteria for a ‘‘light cupula’’ of the LSCC were suggested as the presence of geotropic DCPN with long duration in the supine headroll test and the identification of the null plane (9). Because our patients showed geotropic DCPN with prolonged duration in the supine head-roll test, we sought to identify the null plane. The null plane was investigated in only the last nine patients because the concept of a ‘‘light cupula’’ was recently introduced to the authors in 2011. We could identify the null plane as being on the same side as the SSNHL in all nine patients (Table 1, Fig. 1B, Supplementary video 4, http://links.lww.com/MAO/A230). The results of SVV and caloric response, which were performed 3.0 T 1.2 days after the onset of vertigo, were evaluated in all 17 patients. An abnormal SVV (Q2.7 degrees) was observed in five patients (29%), and the amount of SVV deviation was 3.7 T 0.7 degrees (2.9Y4.7 degrees). Abnormal SVV deviated towards the opposite side as the SSNHL in four of five patients (80%, Table 1). Abnormal CP (Q25%) was observed in 11 of 17 patients (65%), in which one patient (patient 6) exhibited abnormal CP on the opposite side as the SSNHL, possibly caused by an excitation of the vestibular function on the affected side. A CRP session was performed once daily (patient 1Y8), which did not seem effective in treating positional vertigo or geotropic DCPN for any patients, even though the severity of positional vertigo and the intensity of nystagmus gradually improved. It took 5.3 T 1.6 days (2Y8 d, n = 17) for the positional vertigo and nystagmus to be resolved (Table 1). DISCUSSION In the present study, we showed 17 patients with ipsilateral SSNHL simultaneously (within 24 h) accompanied by positional vertigo and showing geotropic DCPN in the supine head-roll test. The geotropic DCPN had a prolonged duration (17 of 17 patients), and the null plane was identified on the same side as the hearing loss (nine of nine patients), which met the diagnostic criteria of a light cupula of the LSCC (9).
Although the causes of both SSNHL and BPPV are idiopathic in most cases, inner ear organs involving the cochlear or vestibular endolymphatic system are thought to be responsible for the pathophysiology of the diseases. Previous reports on ipsilateral SSNHL with simultaneous BPPV suggested that selective damage of the cochlea, which causes SSNHL, and the utricle, which results in otoconial dislodgement, may be responsible for the development of this condition (7,8,16). However, the evidence for utricular damage on the same side as the SSNHL could be observed in only 1 of 17 patients, even though normal static SVV cannot exclude utricular damage in BPPV patients (17,18). Rambold et al. described two patients with ipsilateral SSNHL and positional vertigo showing geotropic DCPN which had a prolonged duration (up to 4 min) (7). The intensity of nystagmus was stronger when the heads were turned towards the side of hearing loss, and the nystagmus did not fatigue on repeated testing. However, identification of the null plane was not attempted (7). In the present study, the patients with SSNHL showing persistent geotropic DCPN could be diagnosed as a light cupula on the side of the SSNHL. Thus, positional vertigo accompanied by SSNHL can be attributed to a light cupula, even though it is unclear whether this condition is a cause of SSNHL. Central lesions involving cerebellar nodulus/uvula or the region dorsolateral to the fourth ventricle have been reported to cause paroxysmal positional nystagmus (19). In any of our patients in this study, thorough neurological examination including cerebellar function test did not reveal abnormal findings, and brain MRI did not show any acute brain lesions or white matter lesions. A light cupula indicates the condition that the specific gravity of the cupula is lower than the surrounding endolymph, which renders hair cells under the cupula to be either activated or inhibited according to the head position in the gravitational vector. It is presumed that the LSCC is the principal test organ in a light cupula (20), even though the vertical and torsional components of nystagmus can be observed in some patients. Although the etiology of a light cupula is still not clear, a change in density and viscosity of the endolymph by inner ear hypoperfusion has been suggested as a possible cause of a light cupula (12). Inflammatory cells or water-soluble macromolecules such as proteoglycans in the endolymphatic space might change the specific gravity of the endolymph (9). It has been proposed that SSNHL with vertigo is caused by the transmission of biochemical changes in the inner ear fluid from the cochlea to the vestibular organs (21). Findings obtained using three-dimensional fluidattenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI) provided supporting evidence that a pathologic alteration occurs within the inner ear fluid in SSNHL patients with or without vertigo, in which high pre-contrast signals were observed within the inner ear on 3D-FLAIR (22,23). Pre-contrast high signals on 3DFLAIR may reflect a minor hemorrhage or an increased inner ear concentration of proteins that were extravasated through blood vessels with increased permeability
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SSNHL WITH PERSISTENT GEOTROPIC DCPN or originated from damaged cells in the inner ear (24). Interestingly, positive findings on 3D-FLAIR MRI were observed in the vestibule and/or SCCs in SSNHL patients with vertigo symptoms, though the clinical characteristics of vertigo and the results of the vestibular function tests were not described in detail (22Y25). A disruption of the blood-labyrinth barrier, which is similar to the bloodbrain barrier and known to be associated with the endothelial cell transport system, may result in leakage of plasma proteins from the inner ear vessels (26,27). As impairment of cerebral blood flow caused an increase in the permeability of the blood-brain barrier (28), inner ear ischemia or hypoperfusion may elicit increased permeability of the blood-labyrinth barrier. The stria vascularisjstrial vessel barrier was reported as an important vessel barrier in the inner ear, which can be disrupted by acoustic trauma causing strial edema (29). Moreover, acute inner ear ischemia in an animal model caused degeneration of strial marginal cells (30), which may change the biochemical properties of the endolymph and disturb endolymphatic homeostasis. Severe disruption of the blood-labyrinth barrier was demonstrated in an animal model of meningogenic suppurative labyrinthitis (31), and increased protein content in the inner ear fluid was shown on 3D-FLAIR MRI in patients with inflammation-induced sensorineural hearing loss (32). Thus, disruption of the blood-labyrinth barrier may be caused by various factors including microcirculatory compromise, inflammation, and acoustic trauma, which may lead to an increase in protein concentration within the endolymphatic space. Findings compatible with a hemorrhage or increased protein concentration in the ampullar endolymph of the PSCC and LSCC on 3D-FLAIR was reported in a patient with SSNHL with vertigo (23). A small hemorrhage or increased protein content within the endolymphatic space, regardless of the etiology, would change the specific gravity of the endolymph. In normal individuals, no difference could be detected between the specific gravity of the endolymph and that of the cupula, and the specific gravity of the endolymph was reported as 1.0033 (33). At 37-C, the specific gravity of the whole blood and plasma are 1.0506 and 1.0205, respectively (34), which is higher than the specific gravity of the endolymph. Thus, a mixture of endolymph and plasma proteins from a small hemorrhage or extravasation of plasma into the endolymphatic space may increase the specific gravity of the endolymph, which will result in a light cupula. Although it is not clear if our patients had small hemorrhages or increased protein concentrations in the endolymphatic space because 3D-FLAIR MRI was not checked in any of our patients, we suggest that the aforementioned changes in the endolymphatic space may be responsible for positional vertigo with persistent geotropic DCPN in our patients. CONCLUSION In patients with SSNHL and simultaneous positional vertigo showing persistent geotropic DCPN in the supine
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head-roll test, a light cupula may be responsible for the development of positional vertigo. In these cases, the intensity of nystagmus is stronger on head-turning towards the affected side, and the null plane can be identified on the same side as the hearing loss. A light cupula may be associated with an increased protein concentration within the endolymphatic space, which could be caused by a small hemorrhage or the extravasation of blood plasma. Acknowledgment: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2044883).
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28. Sadoshima S, Fujishima M, Ogata J, et al. Disruption of bloodbrain barrier following bilateral carotid artery occlusion in spontaneously hypertensive rats. A quantitative study. Stroke 1983;14:876Y82. 29. Hukee MJ, Duvall AJ 3rd. Cochlear vessel permeability to horseradish peroxidase in the normal and acoustically traumatized chinchilla: a reevaluation. Ann Otol Rhinol Laryngol 1985; 94:297Y303. 30. Ando M, Takeuchi S, Kakigi A, et al. Acute ischemia causes ‘dark cell’ change of strial marginal cells in gerbil cochlea. Cell Tissue Res 2002;309:229Y35. 31. Kastenbauer S, Klein M, Koedel U, et al. Reactive nitrogen species contribute to blood-labyrinth barrier disruption in suppurative labyrinthitis complicating experimental pneumococcal meningitis in the rat. Brain Res 2001;904:208Y17. 32. Sone M, Mizuno T, Naganawa S, et al. Imaging analysis in cases with inflammation-induced sensorineural hearing loss. Acta Otolaryngol 2009;129:239Y43. 33. Money KE, Sokoloff M, Weaver RS. Specific gravity and viscosity of endolymph and perilymph. In: NASA, Second Symposium on the Role of the Vestibular Organs. Washington, DC: NASA; 1966:91Y8. 34. Trudnowski RJ, Rico RC. Specific gravity of blood and plasma at 4 and 37 degrees C. Clin Chem 1974;20:615Y6.
Otology & Neurotology, Vol. 35, No. 9, 2014
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Sudden Sensorineural Hearing Loss With Simultaneous Positional Vertigo Showing Persistent Geotropic Direction-Changing Positional Nystagmus *Chang-Hee Kim, *Jee Min Choi, *Hyo Vin Jung, †Hong Ju Park, and *Jung Eun Shin *Department of OtorhinolaryngologyYHead and Neck Surgery, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea; and ÞAsan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
Objectives: To characterize the clinical features of patients who simultaneously developed ipsilateral sudden sensorineural hearing loss (SSNHL) and positional vertigo showing geotropic directionchanging positional nystagmus (DCPN) on a supine head-roll test, and to address the possible pathophysiology of the disease. Study Design: Retrospective case series review. Methods: We conducted a retrospective case series study in 17 patients with SSNHL and simultaneous positional vertigo showing geotropic DCPN. Results: All 17 patients showed persistent geotropic DCPN without latency in the supine head-roll test. The intensity of nystagmus was stronger when the patient’s head was turned to the lesion side of SSNHL in 15 of 17 patients. We sought to identify a null plane in
nine patients, and the null plane was identified on the same side as the SSNHL in all nine patients, which was thought to be caused by the ‘‘light cupula’’ of the lateral semicircular canal in the same ear as the SSNHL. Conclusion: A light cupula mechanism may be one of the causes of positional vertigo in patients with SSNHL. In these cases, persistent geotropic DCPN is observed in the supine head-roll test and the null plane can be identified on the same side as the hearing loss. Key Words: Benign paroxysmal positional vertigoVHeadroll testVPersistent geotropic direction-changing positional nystagmusVPositional vertigoVSudden sensorineural hearing loss. Otol Neurotol 35:1626Y1632, 2014.
Sudden sensorineural hearing loss (SSNHL) is characterized by sensorineural hearing loss of at least 30 dB in three contiguous audiometric frequencies occurring over 3 days or less (1). Although the etiology of SSNHL is still idiopathic, viral infection, labyrinthine ischemia, labyrinthine hemorrhage, and disruption of the cochlear membrane are believed to account for most of the pathophysiology (2). Considering that the lesion site lies within the inner ear organs (2), which are interconnected through the endolymph and surrounding membranes, disturbances of both cochlear and vestibular function may occur simultaneously. Benign paroxysmal positional vertigo (BPPV), which is characterized by a brief episode of rotatory vertigo and nystagmus elicited by a change in head position, can be
simultaneously accompanied by SSNHL in 5 to 19% of all SSNHL patients (3Y6). While the posterior semicircular canal (PSCC) was the most commonly involved canal in some reports (3), the lateral semicircular canal (LSCC) was the most commonly involved canal in others (4,5). In terms of hearing recovery, the presence of BPPV was a poor prognostic factor in some reports (3,6), whereas it was not a prognostic factor in other reports (4,5). Compared with idiopathic BPPV, BPPV with SSNHL required a larger number of canalith repositioning procedures (CRPs) for successful treatment, and consequently showed longer disease durations (3). Thus, clinical features are different between idiopathic BPPV and secondary BPPV associated with SSNHL, which may raise the possibility that the pathophysiology of positional vertigo may differ. Previous reports on simultaneous BPPV with SSNHL suggested that selective damage to the cochlea and the utricle may be the causes of the specific clinical findings (7,8). Viral neurolabyrinthitis instead of labyrinthine infarction was thought to be more compatible with this ‘‘patchy’’ loss of inner ear function.
Address correspondence and reprint requests to Chang-Hee Kim, M.D., Ph.D., Department of OtorhinolaryngologyYHead and Neck Surgery, Konkuk University Medical Center, Konkuk University School of Medicine, 120-1 Neungdong-ro (Hwayang-dong), Gwangjin-gu, Seoul, Korea 143-729; E-mail: [email protected] The authors disclose no conflicts of interest. Supplemental digital content is available in the text.
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SSNHL WITH PERSISTENT GEOTROPIC DCPN Direction-changing positional nystagmus (DCPN) is typically observed in patients with LSCC BPPV when the patient’s head is turned to either side in the supine position (the supine head-roll test). In canalolithiasis-type LSCC BPPV, DCPN beats toward the lowermost ear (geotropic), which is transient with a latency of a few seconds, and weakens after repetitive examination (demonstrates fatigability). Recently, the concept of a ‘‘light cupula’’ in the LSCC that shows persistent geotropic DCPN has been introduced (9Y12). Previously, patients with SSNHL and simultaneous positional vertigo showing geotropic DCPN in the supine head-roll test have been reported (7,13), and the characteristics of geotropic DCPN were as follows: (1) the duration of nystagmus was prolonged, (2) the intensity was stronger upon turning the head towards the side of hearing loss, and (3) the nystagmus did not fatigue on repeated testing. In the present study, we report 17 patients with ipsilateral SSNHL and simultaneous positional vertigo showing persistent geotropic DCPN. Clinical characteristics are described, and a possible mechanism of this condition is discussed. SUBJECTS AND METHODS Subjects We evaluated 17 patients (nine men and eight women; mean age, 49 yr; range, 22Y72 yr) with ipsilateral SSNHL and simultaneous BPPV showing geotropic DCPN between June 2006 and September 2013. All patients met the clinical diagnostic criteria for SSNHL, which is defined as sensorineural hearing loss of 30 dB or more over at least three contiguous frequencies developing within 3 days. Determination of the hearing level in the affected ear was based on the opposite healthy ear. The vertigo attack occurred almost simultaneously with the onset of hearing loss (within 24 h). The study was approved by the Institutional Review Board (KUH1110032). The medical history of each patient was thoroughly investigated, and a neuro-otological examination was performed. Otoscopic examination revealed normal tympanic membrane without any evidence of acute or chronic otitis media in all patients. They denied recent head trauma or surgery, and did not complain of meningitis symptoms such as headache and neck stiffness. Neurological examinations revealed no abnormality in any of the patients. All 17 patients took brain MRI, which did not reveal acute infarction or other acute brain lesions in any of the patients. None of the patients reported taking medicines that may influence vestibular function, including vestibular suppressants, at least 24 hours before the examination. All patients were administered systemic high-dose steroids (prednisolone 1 mg/kg/d for 4 d, and then tapered off during the subsequent 10 d). Some patients subsequently received an intratympanic steroid injection as a salvage treatment.
Audiometry The pure-tone average (PTA) was measured as the average threshold at 500, 1,000, 2,000, and 3,000 Hz. Audiograms were categorized as high-tone, low-tone, flat type, or profound hearing loss. When a patient’s audiogram showed an average loss of 4 to 8 kHz from an average of 0.25 to 0.5 kHz by 30 dB or more, the type of hearing loss was classified as ‘‘high-tone hearing loss.’’ The ‘‘low-tone hearing loss’’ group demonstrated an average loss
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of 0.25 to 0.5 kHz, surpassing the average of 4 to 8 kHz by 30 dB or more. The ‘‘flat-type’’ group consisted of patients with a difference of 20 dB or less between the worst and best hearing levels at six frequencies (0.25, 0.5, 1, 2, 4, and 8 kHz). In the group with profound hearing loss, at least two frequencies produced results that were off the scale, and the difference between the hearing level and maximum sound level generated by the audiometer was within 10 dB at all six frequencies (14). The final PTA was recorded at 3 months after treatment, and hearing recovery was assessed according to the Siegel classification system (15).
Examination of Positional Nystagmus and Vestibular Function Tests The patient’s eye movement was examined at various head positions using Frenzel glasses or goggles installed with an infrared camera (SLMED, Seoul, Korea) by otolaryngologists at the clinic. Then horizontal nystagmus was documented using a videobased system in some patients (CHARTR VNG; ICS Medical, Schaumburg, IL) to calculate the slow-phase velocity (SPV) of nystagmus. All 17 patients underwent the following positioning sequence: (1) the patient lies down in the supine position, (2) the patient’s head is turned to the right over 90 degrees in the supine position, and (3) the patient’s head is turned to the left over 90 degrees in the supine position. Heads were turned to the right or left over about 20 degrees (15Y25 degrees) in the supine position to find the null plane in nine patients. Nystagmus was examined for at least 2 minutes at each position, and the head movement was paused for more than 1 minute in the supine position without any neck rotation between the positioning maneuvers. A bithermal caloric test was performed while recording eye movements using an infrared video-based system. Each ear was irrigated with a constant flow of water at alternating temperatures of 30-C and 44-C for a constant period of time (30 s). The maximum slow-phase velocity (mSPV) of nystagmus was calculated after each irrigation, and Jongkees’ formula was used to determine canal paresis (CP). A CP 25% or greater was considered abnormal. The method of evaluation of the static subjective visual vertical (SVV) was described previously (14). Briefly, in the dark, a dim white line was displayed on a computer monitor, which was placed 100 cm away from the patient. The line was 3 mm wide and 230 mm long, and a dot (3 mm in diameter) was superimposed on the line along the center of the line’s rotational axis. The patients were seated upright on a chair, and their heads were stabilized using a neck rest. The subjects were asked to adjust the visual rod to the vertical position by manipulating a remote controller held in both hands. During each test, the line was offset approximately 10 to 40 degrees clockwise or counterclockwise in a random order. When the line appeared vertical, the subject was instructed to click an enter button, which would automatically calculate the deviation in degrees from the true gravitational vertical. The mean of five tests was used as a measure of SVV tilt, and we considered this value to be abnormal if the tilt was 2.7 degrees or greater (14).
RESULTS Audiologic Characteristics of SSNHL Patients With Positional Vertigo Showing Persistent Geotropic DCPN All patients complained of ipsilateral sudden hearing loss and positional vertigo. Vertigo developed after the onset Otology & Neurotology, Vol. 35, No. 9, 2014
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R R R R R R R L R R R L R L L R R
115 85 92.5 57.5 95 115 115 92.5 56.3 115 61.3 115 115 113.8 48.8 115 110
0 0 0 32 0 0 0 0 36 0 80 0 0 0 80 0 0
Profound Flat-type Flat-type High-tone High-tone Profound Profound Flat-type High-tone Profound Flat-type Profound Profound Profound High-tone Profound Profound
Type of HL 111 88.8 86.3 15 61.3 113 78.8 36.3 43.8 115 30 88.8 96.3 103 27.5 115 91.3
0 0 0 92 44 0 0 76 48 0 92 8 0 0 96 0 0
G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24 G24
Final Final Period from PTA (dB) SDS (%) HL to V (h) Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent Persistent
geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN geotropic DCPN
HR Y (10:10) R (89:16) R (8:5) Y (17:17) R (41:36) R (8:6) R (28:16) L (4:2) R (15:8) R (24:15) R (15:8) L (41:36) R (108:49) L (5:15) L (12:20) R (40:18) R (21:16)
LB (2) LB (7) LB (3) LB (6) LB (11) LB (2) LB (4) RB (1) LB (4) LB (5) LB (4) RB (2) LB (14) RB (4) RB (7) LB (5) LB (5)
NT NT NT NT NT NT NT NT R R R L R L L R R
Strong Supine side on HR (SPV, degrees Side of (SPV, R:L) per second) null plane
Positional nystagmus
Summary of clinical characteristics and test results of the patients (n = 17)
L4.7 Normalb Normal Normal Normal L2.9 Normal Normal Normal R3.6 Normal Normal Normal R3.4 Normal Normal L3.7
Caloric CP (%) Normala Normal R29 R58 R35 L36 Normal L30 Normal R68 Normal Normal R25 L75 L47 R96 R51
5 6 7 5 8 6 5 7 7 3 3 5 5 6 2 6 4
Symptom duration of SVV positional (degrees) vertigo (d)
‘‘R’’ or ‘‘L’’ before the SVV values indicate that the subjective visual vertical was tilted to the patient’s right or left side, respectively. ‘‘R’’ or ‘‘L’’ before the caloric CP values indicate that canal paresis was observed on the patient’s right or left side, respectively. SSNHL indicates sudden sensorineural hearing loss; PTA, pure-tone average; SDS, speech discrimination score; HL, hearing loss; V, vertigo; HR, supine head-roll test; SPV, maximal slow phase velocity (degrees per second); CP, canal paresis; SVV, static subjective visual vertical; L, left; R, right; DCPN, direction-changing positional nystagmus; RB, right-beating; LB, left-beating; NT, not tested. a A CP of less than 25% was considered normal. b A SVV of less than 2.7 degrees was considered normal.
1/M/72 2/F/68 3/M/61 4/M/48 5/F/52 6/F/64 7/F/22 8/M/40 9/M/39 10/F/56 11/M/55 12/F/51 13/F/40 14/M/52 15/F/50 16/M/67 17/M/25
Patient Initial Initial no./sex/age (yr) Side PTA (dB) SDS (%)
SSNHL
TABLE 1.
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Otology & Neurotology, Vol. 35, No. 9, 2014
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SSNHL WITH PERSISTENT GEOTROPIC DCPN of sudden hearing loss in all 17 patients. The positional nystagmus results and clinical characteristics are shown in Table 1. The male-to-female ratio was 9:8. Among the 17 patients, profound hearing loss was the most common type of hearing loss, and was observed in 9 patients (53%), which was consistent with previous observation (5). Both flat-type and high-tone hearing loss were observed in four patients (24%), each. None of the patients exhibited low-tone hearing loss. The initial PTA
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was 93.2 T 28.7 dB (n = 17), and mean speech discrimination score was 13.4 T 27.5%. Three months after treatment, the mean hearing threshold was 76.5 T 33.9 dB (n = 17), which was significantly different from the initial hearing threshold ( p = 0.001, paired t test). The improvement in the hearing threshold was 18.6 T 17.1 dB (n = 17). The hearing recovery rates were classified as complete recovery (n = 1), partial recovery (n = 3), slight recovery (n = 5), or no recovery (n = 8)
FIG. 1. SSNHL on the left side and simultaneous positional vertigo with persistent geotropic DCPN. In the upper panels, the left LSCC and the patient’s head viewed from the top of the patient’s head are depicted. In the lower panels, the video-nystagmographic findings of patient 14 are shown, who exhibited positional nystagmus compatible with a light cupula of the left LSCC. In supine position (A), right-beating nystagmus (maximal SPV = 4 degrees per second) was persistently observed due to utriculofugal deflection of the cupula. B, When the head was slightly turned (20 degrees) to the left side, the nystagmus disappeared (only artifacts from the patient’s eye blinking are shown). In this null plane, the cupula is aligned within the plane of the gravitational vector. C, When the head was turned to the left in the supine position, left LSCC was activated because of utriculopetal deflection of the cupula, and geotropic nystagmus (maximal SPV = 15 degrees per second) was observed. Note that the directions of nystagmus in the supine position and in left head-rolling are opposite to each other. D, The cupula of the left LSCC was deflected utriculofugally when the head was turned to the right side in the supine position, which caused geotropic nystagmus (maximal SPV = 5 degrees per second). Note that the intensity of nystagmus is stronger in left head-rolling than in right head-rolling. SSNHL, sudden sensorineural hearing loss; DCPN, direction-changing positional nystagmus; LSCC, lateral semicircular canal; SPV, slow-phase velocity. Otology & Neurotology, Vol. 35, No. 9, 2014
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according to Siegel’s criteria. Mean speech discrimination score was 26.8 T 38.7% after treatment. Characteristics of Positional Nystagmus In the supine head-roll test, geotropic DCPN with prolonged duration was observed in all patients (Fig. 1C and D, Supplementary videos 1 and 2, http://links.lww.com/MAO/A227 and http://links.lww.com/MAO/A228). We compared the mSPV of nystagmus on head-turning to the right with that to the left, and a stronger side was recognized in 15 of 17 patients (88%), and was on the same side as the SSNHL (Table 1). In the supine position, all 17 patients showed persistent nystagmus beating in the opposite direction of the SSNHL (Table 1, Fig. 1A, Supplementary video 3, http://links.lww.com/MAO/A229). Recently, the concept of a ‘‘light cupula’’ of the LSCC has been introduced (9Y12), even though the pathophysiology is still not clear. The diagnostic criteria for a ‘‘light cupula’’ of the LSCC were suggested as the presence of geotropic DCPN with long duration in the supine headroll test and the identification of the null plane (9). Because our patients showed geotropic DCPN with prolonged duration in the supine head-roll test, we sought to identify the null plane. The null plane was investigated in only the last nine patients because the concept of a ‘‘light cupula’’ was recently introduced to the authors in 2011. We could identify the null plane as being on the same side as the SSNHL in all nine patients (Table 1, Fig. 1B, Supplementary video 4, http://links.lww.com/MAO/A230). The results of SVV and caloric response, which were performed 3.0 T 1.2 days after the onset of vertigo, were evaluated in all 17 patients. An abnormal SVV (Q2.7 degrees) was observed in five patients (29%), and the amount of SVV deviation was 3.7 T 0.7 degrees (2.9Y4.7 degrees). Abnormal SVV deviated towards the opposite side as the SSNHL in four of five patients (80%, Table 1). Abnormal CP (Q25%) was observed in 11 of 17 patients (65%), in which one patient (patient 6) exhibited abnormal CP on the opposite side as the SSNHL, possibly caused by an excitation of the vestibular function on the affected side. A CRP session was performed once daily (patient 1Y8), which did not seem effective in treating positional vertigo or geotropic DCPN for any patients, even though the severity of positional vertigo and the intensity of nystagmus gradually improved. It took 5.3 T 1.6 days (2Y8 d, n = 17) for the positional vertigo and nystagmus to be resolved (Table 1). DISCUSSION In the present study, we showed 17 patients with ipsilateral SSNHL simultaneously (within 24 h) accompanied by positional vertigo and showing geotropic DCPN in the supine head-roll test. The geotropic DCPN had a prolonged duration (17 of 17 patients), and the null plane was identified on the same side as the hearing loss (nine of nine patients), which met the diagnostic criteria of a light cupula of the LSCC (9).
Although the causes of both SSNHL and BPPV are idiopathic in most cases, inner ear organs involving the cochlear or vestibular endolymphatic system are thought to be responsible for the pathophysiology of the diseases. Previous reports on ipsilateral SSNHL with simultaneous BPPV suggested that selective damage of the cochlea, which causes SSNHL, and the utricle, which results in otoconial dislodgement, may be responsible for the development of this condition (7,8,16). However, the evidence for utricular damage on the same side as the SSNHL could be observed in only 1 of 17 patients, even though normal static SVV cannot exclude utricular damage in BPPV patients (17,18). Rambold et al. described two patients with ipsilateral SSNHL and positional vertigo showing geotropic DCPN which had a prolonged duration (up to 4 min) (7). The intensity of nystagmus was stronger when the heads were turned towards the side of hearing loss, and the nystagmus did not fatigue on repeated testing. However, identification of the null plane was not attempted (7). In the present study, the patients with SSNHL showing persistent geotropic DCPN could be diagnosed as a light cupula on the side of the SSNHL. Thus, positional vertigo accompanied by SSNHL can be attributed to a light cupula, even though it is unclear whether this condition is a cause of SSNHL. Central lesions involving cerebellar nodulus/uvula or the region dorsolateral to the fourth ventricle have been reported to cause paroxysmal positional nystagmus (19). In any of our patients in this study, thorough neurological examination including cerebellar function test did not reveal abnormal findings, and brain MRI did not show any acute brain lesions or white matter lesions. A light cupula indicates the condition that the specific gravity of the cupula is lower than the surrounding endolymph, which renders hair cells under the cupula to be either activated or inhibited according to the head position in the gravitational vector. It is presumed that the LSCC is the principal test organ in a light cupula (20), even though the vertical and torsional components of nystagmus can be observed in some patients. Although the etiology of a light cupula is still not clear, a change in density and viscosity of the endolymph by inner ear hypoperfusion has been suggested as a possible cause of a light cupula (12). Inflammatory cells or water-soluble macromolecules such as proteoglycans in the endolymphatic space might change the specific gravity of the endolymph (9). It has been proposed that SSNHL with vertigo is caused by the transmission of biochemical changes in the inner ear fluid from the cochlea to the vestibular organs (21). Findings obtained using three-dimensional fluidattenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI) provided supporting evidence that a pathologic alteration occurs within the inner ear fluid in SSNHL patients with or without vertigo, in which high pre-contrast signals were observed within the inner ear on 3D-FLAIR (22,23). Pre-contrast high signals on 3DFLAIR may reflect a minor hemorrhage or an increased inner ear concentration of proteins that were extravasated through blood vessels with increased permeability
Otology & Neurotology, Vol. 35, No. 9, 2014
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SSNHL WITH PERSISTENT GEOTROPIC DCPN or originated from damaged cells in the inner ear (24). Interestingly, positive findings on 3D-FLAIR MRI were observed in the vestibule and/or SCCs in SSNHL patients with vertigo symptoms, though the clinical characteristics of vertigo and the results of the vestibular function tests were not described in detail (22Y25). A disruption of the blood-labyrinth barrier, which is similar to the bloodbrain barrier and known to be associated with the endothelial cell transport system, may result in leakage of plasma proteins from the inner ear vessels (26,27). As impairment of cerebral blood flow caused an increase in the permeability of the blood-brain barrier (28), inner ear ischemia or hypoperfusion may elicit increased permeability of the blood-labyrinth barrier. The stria vascularisjstrial vessel barrier was reported as an important vessel barrier in the inner ear, which can be disrupted by acoustic trauma causing strial edema (29). Moreover, acute inner ear ischemia in an animal model caused degeneration of strial marginal cells (30), which may change the biochemical properties of the endolymph and disturb endolymphatic homeostasis. Severe disruption of the blood-labyrinth barrier was demonstrated in an animal model of meningogenic suppurative labyrinthitis (31), and increased protein content in the inner ear fluid was shown on 3D-FLAIR MRI in patients with inflammation-induced sensorineural hearing loss (32). Thus, disruption of the blood-labyrinth barrier may be caused by various factors including microcirculatory compromise, inflammation, and acoustic trauma, which may lead to an increase in protein concentration within the endolymphatic space. Findings compatible with a hemorrhage or increased protein concentration in the ampullar endolymph of the PSCC and LSCC on 3D-FLAIR was reported in a patient with SSNHL with vertigo (23). A small hemorrhage or increased protein content within the endolymphatic space, regardless of the etiology, would change the specific gravity of the endolymph. In normal individuals, no difference could be detected between the specific gravity of the endolymph and that of the cupula, and the specific gravity of the endolymph was reported as 1.0033 (33). At 37-C, the specific gravity of the whole blood and plasma are 1.0506 and 1.0205, respectively (34), which is higher than the specific gravity of the endolymph. Thus, a mixture of endolymph and plasma proteins from a small hemorrhage or extravasation of plasma into the endolymphatic space may increase the specific gravity of the endolymph, which will result in a light cupula. Although it is not clear if our patients had small hemorrhages or increased protein concentrations in the endolymphatic space because 3D-FLAIR MRI was not checked in any of our patients, we suggest that the aforementioned changes in the endolymphatic space may be responsible for positional vertigo with persistent geotropic DCPN in our patients. CONCLUSION In patients with SSNHL and simultaneous positional vertigo showing persistent geotropic DCPN in the supine
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head-roll test, a light cupula may be responsible for the development of positional vertigo. In these cases, the intensity of nystagmus is stronger on head-turning towards the affected side, and the null plane can be identified on the same side as the hearing loss. A light cupula may be associated with an increased protein concentration within the endolymphatic space, which could be caused by a small hemorrhage or the extravasation of blood plasma. Acknowledgment: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2044883).
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