Medical Hypotheses 83 (2014) 541–544

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‘‘Light cupula’’ involving all three semicircular canals: A frequently misdiagnosed disorder q Chang-Hee Kim a, Jung Eun Shin a, Dong Hyuk Shin a, Yong Won Kim a, Jae Ho Ban b,⇑ a b

Department of Otorhinolaryngology-Head and Neck Surgery, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, South Korea Department of Otorhinolaryngology-Head and Neck Surgery, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, South Korea

a r t i c l e

i n f o

Article history: Received 23 February 2014 Accepted 4 September 2014

a b s t r a c t Though benign paroxysmal positional vertigo (BPPV) is the most common vestibular disorder causing positional vertigo, patients with typical positional vertigo in which the findings of positional nystagmus do not meet the diagnostic criteria for BPPV are often encountered in the clinic. Recently a concept of the light cupula was introduced, which accounts for some of positional vertigo. Under a normal condition in which the specific gravity of the cupula is same as that of the surrounding endolymph, semicircular canals (SCCs) are not influenced by the gravity. The light cupula, which indicates cupula with lower specific gravity than the surrounding endolymph, is characterized by persistent geotropic direction-changing positional nystagmus (DCPN) without latency on the supine head-roll test and the presence of a null plane. Unless the duration and pattern of positional nystagmus are carefully examined, the light cupula can be misdiagnosed as other types of BPPV. We present a patient with light cupula on the right side who reported recurrent episodes of positional vertigo and had been diagnosed as BPPV with multiple canal involvement (posterior and lateral SCCs) on the opposite side. In this study, we present the mechanism of typical positional nystagmus patterns in patients with light cupula involving all of the unilateral SCCs, and discuss the possible causes of misdiagnosis of the light cupula. Ó 2014 Elsevier Ltd. All rights reserved.

Introduction/background Benign paroxysmal positional vertigo (BPPV), which is characterized by a brief episode of rotatory vertigo and nystagmus elicited by a change in head position, is the most common cause of positional vertigo, and dislodged otoconia from the utricle is accepted as the cause of BPPV. However, patients with typical positional vertigo in which the findings of positional nystagmus do not meet the diagnostic criteria for BPPV are often encountered in the clinic. Recently a concept of the light cupula has been introduced, which accounts for some of positional vertigo [1–5]. The light cupula indicates the cupula with lower specific gravity than the surrounding endolymph of which specific gravity is same as that of the cupula under normal condition. The light cupula can be misdiagnosed as the canalolithiasis type of lateral semicircular canal q This study was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2044883). ⇑ Corresponding author at: Department of Otolaryngology-Head & Neck Surgery, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, 108 Pyoung-Dong, Jong-no-Gu, Seoul 110-746, South Korea. Tel.: +82 2 2001 2267; fax: +82 2 2001 2273. E-mail address: [email protected] (J.H. Ban).

http://dx.doi.org/10.1016/j.mehy.2014.09.002 0306-9877/Ó 2014 Elsevier Ltd. All rights reserved.

(LSCC) BPPV. The canalolithiasis type of LSCC BPPV typically exhibits transient geotropic direction-changing positional nystagmus (DCPN), in which the fast phase of the nystagmus is towards the lowermost ear (geotropic) upon head turning to either side in the supine position (head-roll test). Gravity-dependent movement of otolith particles within the LSCC, as in other types of BPPV, has been accepted as a possible mechanism for the geotropic DCPN in canalolithiasis. The geotropic DCPN of LSCC canalolithiasis is transient, has latency of a few seconds, and is either weakened or lost after repetitive examination (fatigability). On the other hand, the nystagmus observed in the light cupula, which also exhibits geotropic DCPN on the head-roll test, is persistent without latency or fatigability [1–6]. The percentage of patients with geotropic DCPN due to the light cupula has been reported to be as high as 14.2% [1]; however, this disease entity has been somewhat underestimated in the differential diagnosis of positional vertigo. In fact, differential diagnosis between the light cupula and the canalolithiasis type of LSCC BPPV is difficult unless the latency and persistency of the nystagmus are carefully examined on the supine head-roll test. The condition of the light cupula renders the cupula gravitysensitive and results in deflection of the cupula according to the alignment between the axis of the cupula and the direction of

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gravity. While SCCs are gravity-independent under normal condition, SCCs are activated or inhibited according to the head position in the condition of the light cupula. Because the organs within the inner ear are interconnected through the endolymph and surrounding membrane, the condition of light cupula may involve all 3 SCCs and otolith organs on the affected side. In this case, the analysis of eye movement is complicated because of the mixture of the vertical and torsional components, and may lead to misdiagnosis. In the present study, we report a patient with the light cupula involving all of 3 SCCs on the right side, and discuss the possible causes of misdiagnosis.

Case presentation A 42-year-old woman visited our dizziness clinic complaining of sudden onset of positional vertigo. The patient reported recurrent episodes (twice a year) of vertigo for the previous 4 years. Each episode of vertigo lasted for 1–4 weeks and was not accompanied by audiologic symptoms such as hearing loss, tinnitus, and ear fullness. At the latest episode, the positional vertigo had begun abruptly 4 days previously, and had deteriorated 1 day before the visit to our clinic. The vertigo was aggravated when the patient turned her head either to the right or left in the supine position. She was diagnosed with BPPV with multiple canal involvement on the left side by the primary physician. More specifically, the diagnosis was BPPV simultaneously involving the LSCC and posterior semicircular canal (PSCC) on the right side. The patient underwent canalith repositioning treatment (CRT) including the modified Epley’s and barbecue maneuvers on the affected side, but her symptoms persisted. Subsequently, the patient was referred to our clinic. Head thrust test was negative for refixation saccade bilaterally, and skew deviation or gaze-evoked nystagmus was not observed. Pure tone audiometry showed no hearing loss on either side, and no neurological deficit was found on a thorough neurologic examination. The patient did not report any previous history of central nervous system disorders such as multiple sclerosis, and brain MRI revealed no abnormality. The patient’s eye movements were examined at the various head positions and recorded using goggles installed with infrared cameras (SLMED, Seoul, Korea). Using ImageJ and a Macintosh computer (Mac OS 10.6.7), 3-dimensional video-oculography was performed [7]. In the sitting position, persistent spontaneous nystagmus with a left-beating horizontal component was mainly observed, but a mild down-beating component was also observed (Fig. 1A). Then, the patient bowed her head at 90° in the sitting position, and strong right-beating nystagmus accompanied by a combination of torsional and vertical components was persistently observed (Fig. 1B). Then, the patient lied down in the supine position, and left-beating nystagmus with mild torsional and vertical components was observed (Fig. 1C). Then, we performed the supine head-roll test on the patient. When the patient’s head was turned to the right or left at 90° in the supine position, persistent geotropic DCPN without latency was observed (Fig. 1D and E). The intensity of geotropic nystagmus was stronger with the head turning to the right (Fig. 1D) than the left (Fig. 1E), and a diagnosis of light cupula on the right side was made by Ewald’s second law [1]. A null plane at which the geotropic nystagmus disappeared could be identified when the patient’s head was slightly (about 35°) turned to the right in the supine position, which indicated that the cupula of the right LSCC is aligned with the direction of the gravity vector [1]. Then, the Dix–Hallpike test was performed with the patient in the sitting position. While only negligible nystagmus was observed on the right Dix–Hallpike test (Fig. 2A), left-beating horizontal nystagmus with a relatively strong torsional component

was provoked on the left Dix–Hallpike test (Fig. 2B), which might have led to misdiagnosis of a combination of PSCC and LSCC BPPV on the left side by the primary physician. Latency or reversal of nystagmus upon returning to the upright position was not observed. A torsional or vertical component at each positional nystagmus was often observed independently without an accompanying horizontal component, which implies that the torsional and vertical components might not have been elicited by activation or inhibition of the LSCC [8]. The patient received vestibular suppressants without any specific treatments such as CRT, but the symptoms persisted for 5 weeks even though the severity of the symptoms gradually lessened. Though the intensity was gradually decreased, the positional nystagmus patterns consisted during that period. Hypotheses A light cupula hypothesis is an emerging new concept accounting for positional vertigo and can be misdiagnosed as other disorders such as BPPV with multiple canal involvement. In case the light cupula involves all 3 SCCs of one side, reaching the correct diagnosis is complicated. We will discuss the reason why the light cupula involving all SCCs can be often misdiagnosed leading to unnecessary treatments such as canalith repositioning maneuver, and address keys for reaching proper diagnosis. Evaluation of hypotheses and discussion The concept of light cupula has been recently introduced for the diagnosis of patients with positional vertigo and persistent DCPN [1–6]. Positional nystagmus with the following characteristics is observed in patients with light cupula: (1) persistent geotropic DCPN without latency on the supine head-roll test, (2) the presence of a null plane at which geotropic nystagmus ceases on slight turning of the patient’s head (15–40°) to the affected side, (3) horizontal nystagmus towards the affected side at the bowing (90° nose-down) position, (4) horizontal nystagmus towards the healthy side when lying down (the supine position), and (5) spontaneous nystagmus towards the healthy side in the sitting position without neck flexion or extension [1–6]. Of these characteristics, persistent geotropic DCPN without latency on the supine head-roll test is the most important diagnostic criterion for the diagnosis of the light cupula [1]. Because the theory of light cupula in the clinical field has been only recently introduced [6] and evidence supporting the theory is indirect, the diagnosis of light cupula might have been disregarded by many clinicians. The clinical practice guidelines for BPPV also do not consider light cupula a differential diagnosis in patients with positional vertigo [9]. Because both light cupula and the canalolithiasis type of LSCC BPPV show geotropic DCPN on the supine head-roll test, careful observation of the latency and duration of geotropic DCPN is crucial for differentiating between the 2 conditions. Although the etiology of the light cupula is still unclear, a change in density of the endolymph due to inner ear hypoperfusion has been suggested as a possible cause of the light cupula [5]. Recently, it was reported that the condition of the light cupula is responsible for the positional vertigo in some patients with sudden sensorineural hearing loss (SSNHL) [2]. Findings obtained using 3dimensional fluid-attenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI) in patients with SSNHL with vertigo indicated a minor hemorrhage or an increased concentration of proteins in the inner ear presumably due to a disruption of the blood-labyrinth barrier [10,11]. The blood-labyrinth barrier has been reported to be disrupted by various causes such as microcirculatory compromise, infection, and acoustic trauma [12–14]. A

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A

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Spontaneous nystagmus (sitting)

C Bowing

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Right head-roll

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Fig. 1. Three-dimensional video-oculography of the patient who was diagnosed with light cupula on the right side. Spontaneous nystagmus with left-beating horizontal and mild down-beating vertical components is observed in the sitting position (A). In the bowing position, nystagmus with strong right-beating horizontal, down-beating vertical, and right torsional components is elicited (B). Left-beating horizontal nystagmus accompanied by mild vertical and torsional components is shown in the supine position (C). When the head is turned to the right in the supine position, strong right-beating nystagmus (D) is observed (SPV = 36°/s). Left-beating nystagmus with less intensity (SPV = 22°/s) is observed when the head is turned to the left in the supine position (E). Note that the vertical and/or torsional components are often temporally independent of the horizontal component of the nystagmus, which indicates that the vertical or torsional component may not originate from the LSCC but from other vestibular organs such as vertical SCCs. SPV, maximal slow-phase velocity.

A

B Right Dix-Hallpike

Left Dix-Hallpike

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V

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Fig. 2. Positional nystagmus during the Dix–Hallpike maneuver. While the nystagmus elicited by the right Dix–Hallpike maneuver is negligible (A), leftbeating horizontal nystagmus with both vertical and torsional components is observed on the left Dix–Hallpike maneuver (B).

leakage of plasma protein into the endolymph from the inner ear vessels may elevate the specific gravity of the endolymph, because the specific gravity of the whole blood (1.0506) or the blood plasma (1.0205) is higher than that of the endolymph (1.0033) [15,16], consequently resulting in the condition of the light cupula. The inner ear organs are interconnected by the endolymphatic membrane within which the endolymphatic fluid is circulated.

Thus, it is reasonable that the condition of the light cupula is not limited to the LSCC but involved in all of 3 SCCs and vestibules. Although horizontal nystagmus is predominant in light cupula, vertical and torsional components may also be observed [4]. Considering that the change in specific gravity of the endolymph may affect all of the inner ear organs, which are interconnected through the endolymph, it is reasonable to assume that the condition of light cupula can involve all 3 SCCs on the affected side. However, vertical and torsional components are mixed and complex because of the combination of activation or inhibition of the vertical SCCs. A high degree of anatomical variation of SCCs between individuals has also been reported [17]. Moreover, the exact alignment of the cupula in the vertical SCCs with respect to the gravity vector has not yet been clearly identified, though the location of the cupula in the horizontal semicircular canal has been reported [18]. The vertical and torsional components of nystagmus in the light cupula have been reported to be elicited by activation or inhibition of the LSCC and influence from the otolithic organs [4]. However, considering that the vertical or torsional component was not always temporally synchronized with the horizontal component in the patient, the complicated positional nystagmus observed in this patient might have originated from the involvement of the light cupula in all 3 SCCs. Considering the location and direction of the axis of the cupula when the patient was sitting, the right LSCC and PSCC were inhibited and the anterior SCC (ASCC) was activated (Fig. 3) resulting in left-beating horizontal and down-beating spontaneous nystagmus (Fig. 1A). On the right Dix–Hallpike test, the right LSCC was minimally activated or inhibited because the cupula was aligned near the null plane, and the deflection of the cupula of the PSCC or ASCC was not considerable, which resulted in only negligible nystagmus (Fig. 2A). On the other hand, on the left Dix–Hallpike test, the right LSCC was inhibited, the ASCC was activated, and the PSCC was minimally influenced, which resulted in mixed left-beating horizontal and left torsional nystagmus accompanied by intermittent downbeating nystagmus (Fig. 2B). In the present patient, the initial diagnosis by the primary physician was a combination of left PSCC BPPV and left LSCC BPPV. The

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ASCC

B LSCC (inhibited)

LSCC

ASCC (activated)

Nystagmus: LB & DB

PSCC (inhibited)

PSCC

Fig. 3. Schematic illustrations showing the direction of cupula deflection in the right semicircular canals in the sitting position. The right LSCC is viewed from the patient’s posterior (left panel of A), and the ASCC and PSCC are viewed from the patient’s right lateral side (right panel of A). Under the condition of the light cupula, the cupula is utriculofugally deflected in the LSCC and ASCC, and utriculopetally deflected in the PSCC (A), which results in activation of the ASCC and inhibition of the LSCC and PSCC (B). Thus, nystagmus with left-beating and down-beating component can be observed as seen in Fig. 1A. Abbreviation: LSCC, lateral semicircular canal; ASCC, anterior semicircular canal; PSCC, posterior semicircular canal; LB, left-beating; DB, down-beating.

misdiagnosis of left PSCC BPPV might have originated from the observation of left torsional nystagmus on the left Dix–Hallpike test and negligible nystagmus on the right Dix–Hallpike test. Left LSCC BPPV might have been misdiagnosed from the observation of geotropic DCPN on the supine head-roll test, in which determining the side of stronger nystagmus intensity may sometimes be difficult without the analysis of slow-phase velocity. However, the diagnosis of light cupula could have been easily made by the observation of persistent geotropic DCPN without latency on the supine head-roll test, and involvement of the right side could have been determined by the observations that the null plane was on the right side, the strong side on the supine head roll was right, and the directions of bowing and lying-down nystagmus were right and left, respectively.

Conclusion The light cupula, which indicates the condition with heavier specific gravity of the endolymph than the cupula, is an emerging concepts accounting for the positional vertigo. When the light cupula involves the LSCC, thorough examination of duration and latency of geotropic DCPN is mandatory for the differential diagnosis from the canalolithiasis type of LSCC BPPV. In case all of 3 semicircular canals are involved with the light cupula, vertical and torsional components are intermingled with the horizontal nystagmus during various positioning maneuvers leading to misdiagnosis as BPPV with multiple canal involvement. Thus, thorough examination of positional nystagmus using videonystagmography (or Frenzel glasses) is important for reaching correct diagnosis of the light cupula.

Conflict of interest The authors have no conflict of interest.

Acknowledgment The authors thank Dr. Hiroaki Ichijo for his technical support for 3-dimensional analysis of the eye movement.

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"Light cupula" involving all three semicircular canals: A frequently misdiagnosed disorder.

Though benign paroxysmal positional vertigo (BPPV) is the most common vestibular disorder causing positional vertigo, patients with typical positional...
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