This study was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science, and Technology (2012R1A1A2044883).
Persistent geotropic direction-changing positional nystagmus with a null plane: The light cupula
Article first published online: 25 OCT 2013
© 2013 The American Laryngological, Rhinological and Otological Society, Inc.
Volume 124, Issue 1, pages E15–E19, January 2014
How to Cite
Kim, C.-H., Kim, M.-B. and Ban, J. H. (2014), Persistent geotropic direction-changing positional nystagmus with a null plane: The light cupula. The Laryngoscope, 124: E15–E19. doi: 10.1002/lary.24048
The authors have no other funding, financial relationships, or conflicts of interest to disclose.
- Issue published online: 20 DEC 2013
- Article first published online: 25 OCT 2013
- Manuscript Accepted: 17 JAN 2013
- Manuscript Revised: 30 DEC 2012
- Manuscript Received: 23 OCT 2012
- Benign paroxysmal positional vertigo;
- direction-changing positional nystagmus;
- head roll test;
- null plane;
- geotropic nystagmus
The aim of this study was to characterize the clinical features and typical positional nystagmus in patients with persistent geotropic direction-changing positional nystagmus (DCPN) and address the possible pathophysiology of the disease. Furthermore, the proportion of light cupula among the patients showing geotropic DCPN was investigated to assume the incidence of light cupula in those patients.
Prospective case series.
We conducted a prospective case series study in 19 patients with persistent geotropic DCPN. Positional nystagmus during the bow and lean test and the supine head roll test was analyzed using videonystagmography.
All of the 19 patients showed persistent geotropic DCPN without latency. A null plane in which the nystagmus ceases was identified in all of 19 patients, and the intensity of nystagmus was stronger on one side in13 patients (68%) on supine head roll test. Overall, the affected side could be identified in 18 patients (95%). About 14.2% (19 of 134) of patients with geotropic DCPN could be diagnosed as having light cupula in the horizontal semicircular canal.
The patients with light cupula show persistent geotropic DCPN without latency. Affected side(s) can be determined by the direction and intensity of the characteristic positional nystagmus and the side of the null plane. The pathophysiology and treatment of light cupula still remain to be elucidated.
Level of Evidence
4. Laryngoscope, 124:E15–E19, 2014
Benign paroxysmal positional vertigo (BPPV) is one of the most common causes of recurrent vertigo and is characterized by transient vertigo and nystagmus elicited by change of head position. Horizontal semicircular canal (HC)-BPPV accounts for about 5.1% to 31.9% of all BPPV patients.[1-3] Direction-changing positional nystagmus (DCPN) is typically observed upon head turning to either side in supine position in patients with HC-BPPV. For cases in which DCPN beats toward the lowermost ear (geotropic), gravity-dependent movement of otolith particles within the HC has been accepted as a possible mechanism (canalolithiasis). Cupulolithiasis in which otolith debris is attached on the cupula has been known to be responsible for the apogeotropic DCPN. The geotropic nystagmus of HC canalolithiasis is transient, has latency of a few seconds, and is either weakened or lost after repetitive examination (fatigability). However, some cases show geotropic DCPN, which is not transient but is persistent without the latency or fatigability as observed in cupulolithiasis. Recently, persistent geotropic DCPN has been reported, which is thought to be due to light cupula of HC.[4-6]
In the present study, we report on 19 patients with light cupula who exhibited persistent geotropic DCPN. Characteristic nystagmus profiles are described, and the mechanism is discussed.
MATERIALS AND METHODS
Nineteen patients (5 males, 14 females; mean age, 55 years; range, 35–75 years) who exhibited geotropic DCPN with null plane were prospectively included in this study. All of the patients complained of positional vertigo and were examined at a tertiary referral hospital between January 2011 and June 2012. The study was approved by the institutional review board (KUH1110025). The medical history of each patient was thoroughly investigated, and neuro-otologic examination was performed. No cochlear symptoms including hearing loss or central nervous system disorder were found. None of the patients reported taking medicine that may influence vestibular function, including vestibular suppressant, at least 24 hours before the examination. Patient eye movement was examined at the various head positions and recorded using a goggle installed with infrared camera (Micromedical, Chatham, IL; SLMED, Seoul, Korea) by otolaryngologists at the clinic, and the diagnosis of light cupula was made. The horizontal nystagmus was then documented by means of a video-based system in some patients (CHARTR VNG; ICS Medical, Schaumburg, IL) to calculate the slow-phase velocity (SPV) of nystagmus. All the patients underwent the following sequence of positioning maneuvers: 1) the patient bows the head for 90 degrees in the sitting position, 2) the patient leans the head backward for 45 degrees in the sitting position, 3) the patient's head is turned to the right for 90 degrees in the supine position, 4) the patient's head is turned to the left for 90 degrees in the supine position, and 5) the patient's head is turned to the right or left about 20 degrees (15–25 degrees) in the supine position to find the null plane. The nystagmus was examined for more than 2 minutes at each position, and the head movement was paused for more than 1 minute in the sitting or supine position without any neck rotation between the positions. The diagnostic criteria for the light cupula were the presence of geotropic DCPN with long duration on supine head-roll test and the identification of a null plane. Brain magnetic resonance imaging was checked in five patients, and no lesion was found in the brain.
All of the patients complained of positional vertigo. Results of positional nystagmus and clinical profiles are shown in Table 1. The male-to-female ratio was 5:14. The persistent geotropic DCPN without latency was observed in all patients on supine head-rolling.
|Patient No.||Sex||Age, yr||Strong Side on Supine Head Rolla||Side of Null Planeb||Bow||Lean||No. of Recurrences||Medication||Symptom Duration, wk|
As for the HC-BPPV, intensity of nystagmus on head roll test may be helpful in determining the involved side by Ewald's second law in patients with light cupula (Fig. 1). Ewald's second law states that ampulopetal stimulation is stronger than ampulofugal inhibition in HC. We examined which side had stronger nystagmus on supine head roll test by comparing the maximal SPV of nystagmus on head-turning to the right with that on head-turning to the left. The stronger side was recognized in 13 patients (68%) and was on the right in 12 and on the left in one. However, in six patients, geotropic DCPN showed same SPV on right and left head roll tests.
A null plane at which the nystagmus disappears could be identified when the patient's head was slightly turned (usually 15–25 degrees) to either the right or left in the supine position (Fig. 2). All of 19 patients showed a null plane, which was on the right side in 13 and on the left side in six patients.
The bow and lean test has been reported to be useful for the determination of the affected ear in HC-BPPV. The patients were subjected to bowing (90 degrees) and leaning (45 degrees) in a sitting position; the side of light cupula is supposed to be same with the direction of “bowing nystagmus.” Bowing nystagmus was observed in 18 of 19 patients (95%), and 17 of them showed “leaning nystagmus.” Of the 17 patients showing both bowing and leaning nystagmus, 16 exhibited bowing and leaning nystagmus with opposite direction, and the direction of bowing nystagmus was the same as the side of the null plane. The bowing and leaning nystagmus were in the same direction in one patient, and the side of the null plane was opposite (patient 2). Schematic illustrations of a typical light cupula model are shown in Figure 1.
Among 19 patients, three patients had experienced one previous episode of positional vertigo, and one patient had experienced recurrent episodes of positional vertigo three times before. Most patients were prescribed with vestibular suppressants for the symptomatic relief. Positional vertigo and nystagmus were improved in 1 week or less in 14 of 19 patients (74%), whereas the signs and symptoms lasted for 3 or 4 weeks in two patients.
Then, we sought to investigate the incidence of light cupula among those who showed geotropic DCPN during the same period (between January 2011 and June 2012). The proportions of light cupula among all types of BPPV, those with DCPN, and those with geotropic DCPN were 4.9% (19 of 388), 9.4% (19 of 202), and 14.2% (19 of 134), respectively.
The theory of light cupula, which indicates cupula with lower specific gravity than the surrounding endolymph, was first introduced from the observation of positional alcohol nystagmus (PAN).[8, 9] After intake of alcohol, which has lower specific gravity than the endolymph, alcohol diffuses into the cupula earlier than the endolymph owing to its proximity to capillaries.[10, 11] This makes the cupula lighter than the surrounding endolymph, which results in the deflection of cupula and geotropic DCPN (early phase of PAN) according to the alignment between the axis of cupula and the direction of gravity.
Recently, the concept of light cupula has been introduced as a variant of HC-BPPV for the diagnosis of patients with positional vertigo.[4-6] The characteristics of nystagmus in these patients are as follows: 1) a null plane at which nystagmus ceases can be found when the patient's head is turned to the affected ear for 20 degrees (±5 degrees), 2) horizontal nystagmus towards the affected side in bowing (nose-down) position, 3) horizontal nystagmus towards the healthy side in leaning or supine position, and 4) persistent geotropic DCPN without latency when the patient's head is turned to the right or left in supine position.[4-6] Under normal conditions, the specific gravity of the endolymph is almost the same with that of cupula, and hair cells in the cupula are not activated or inhibited by the changes of head position with respect to gravity. However, if the cupula is lighter than the endolymph from any possible causes, the cupula may become gravity sensitive. The cupula of horizontal canal is tilted laterally in the sagittal plane (Fig. 1A). Considering the orientation of cupula in horizontal canal, a slight head rotation to one side in the supine position can align the axis of ipsilateral cupula along with the gravitational plane. Thus, the side of null plane always corresponds with the side of light cupula. At this null plane, if only one side is affected, the nystagmus disappears, and the direction of nystagmus is changed by further head rotation. On head roll test, the patients exhibit geotropic nystagmus that is more intense when the head is turned to the affected side (Ewald's second law) (Fig. 1C and 1D). The direction of nystagmus is ipsilesional in bowing and contralesional in leaning (or supine) (Fig. 1A and 1B). Differential diagnosis from the canalolithiasis type of HC-BPPV in which geotropic DCPN is also observed should be made. In this case, the nystagmus occurs with latency of several seconds and is transient, usually lasting less than 1 minute. Moreover, null plane is never found in the canalolithiasis.[12-14]
In the present study, all of the patients exhibited positional vertigo and persistent geotropic DCPN without latency. There were two patients showing persistent geotropic DCPN without latency who were not included in the diagnosis of light cupula. The null plane was thought to be at 0 degrees in these two patients because the nystagmus ceased in the supine position. These two patients were considered to have bilaterally symmetric light cupula. The observation that both the bowing and the leaning nystagmus were not shown in these two patients further supported this assumption. However, the mechanism by which both sides have bilaterally symmetric light cupula is still not clear. So, for clarity, we decided not to include these two patients in the present study according to our diagnostic criteria, as described. The stronger side of nystagmus on head roll test was identified in 13 of 19 patients (68%), and in one of these patients the side of stronger nystagmus and null plane were opposite. Bowing and leaning nystagmus were not observed in this patient, and the affected side could not be determined. From 19 patients, both bowing and leaning nystagmus were observed in 17 patients, and the direction of bowing and leaning was opposite in 16 of these 17 patients. In summary, the diagnosis of light cupula can be easily made from a symptom of positional vertigo and observation of persistent geotropic DCPN on head roll test, and the determination of the affected side can be made by interpreting the results of the side of null plane, strong side on the supine head roll, and bowing and leaning nystagmus. However, the affected side may not be easy to determine in some cases, as we saw in one patient in the present study (patient 14).
For our 19 patients, the male-to-female ratio was 5:14. The predominantly female incidence has been consistently observed in previous studies.[4-6] Of 18 patients whose affected side could be identifiable, 13 patients had light cupula on the right side, and five patients had it on the left side. If the specific gravity of the endolymph could be systemically influenced, a condition such as light cupula would be bilateral. In the present study, the affected side could be identified in most patients (18 of 19); this finding may be due to the possibility that we have different inner ear conditions, including the density of the cupula and/or the endolymph, just as we may have different binocular visual acuity. In cases in which the affected side could not be identified, bilateral involvement of the light cupula to the same extent could be considered as a possible cause. Right side predominance was also observed in a previous study. The patients did not receive any specific treatments such as canalith repositioning maneuver, and most patients (16 of 19) were given vestibular suppressant. The positional vertigo and nystagmus disappeared within 2 weeks in 17 of 19 patients, but the signs and symptoms continued for up to 3 or 4 weeks in two patients.
Among 134 patients who exhibited geotropic DCPN, 19 patients (14.2%, 19 of 134) were diagnosed with light cupula. This finding indicates that light cupula may not be a rare disease entity and may often be misdiagnosed as a canalolithias-type of HC-BPPV in some patients with geotropic DCPN. Considering that the treatment for canalolithiasis—canalith repositioning therapy—is unnecessary in the light cupula, differential diagnosis between light cupula and canalolithiasis is important. In case of light cupula, geotropic DCPN on supine head roll test is persistent without latency, and the direction of nystagmus changes at a null plane in a way that nystagmus directs to the right (or left) when the head is turned to the right (or left) from a null plane (Table 2).
|Light Cupula||HC Canalolithiasis|
The pathophysiology of light cupula still remains to be elucidated. Reversible sensorineural hearing loss was reported to concurrently accompany the light cupula, and the light cupula was followed by ipsilateral stellate ganglion block. Both the sensorineural hearing loss and stellate ganglion block are conditions that may be related to the reduction of blood flow to the inner ear, so the authors speculated that the inner ear hypoperfusion would affect the density or viscosity of the endolymph, resulting in the light cupula. Acute inner ear ischemia in an animal model has been reported to cause degeneration of strial marginal cells, which may disturb the endolymphatic homeostasis, leading to a possible change of specific gravity of endolymph. Inflammatory cells have been reported to be found in endolymphatic space in animal models of inflammation-mediated endolymphatic hydrops and utricular nerve section.[16, 17] If similar conditions of inflammation or injury occur in the human inner ear, the plasma with leukocytes in the endolymph may increase the specific gravity of the endolymph. Water-soluble macromolecules such as proteoglycans are found in the endolymph, and the concentration change of these macromolecules may lead to the alteration of specific gravity of the endolymph. Likewise, under certain conditions, the endolymph could possibly be lighter than the cupula. We speculate that a “heavy cupula” compared to the lighter endolymph could be a part of pathophysiology of apogeotropic DCPN for which otolith particles stuck in the cupula has been considered as a cause.
Although vertical and torsional components of nystagmus were observed in some patients, horizontal nystagmus was predominant in all of the patients. Taking into account the fact that the change of density of endolymph would not be confined to the HC, it is reasonable to assume that positional nystagmus would have vertical and torsional components. However, vertical and torsional components may be mixed and complex owing to the combination of activation or inhibition of vertical semicircular canals. Moreover, the exact alignment of the cupula in the vertical semicircular canals with respect to the gravity vector has not been clearly identified, although the location of cupula in the HC has been reported. Recently it has been proposed that vertical and torsional components originate from the horizontal canal.
Light cupula should be ruled out when the patient shows geotropic DCPN. In contrast with a canalolithiasis type of HC-BPPV, positional nystagmus in the light cupula is persistent and does not have latency. The affected side can be determined mainly by the null point, but it cannot always be clearly identified. The pathophysiology of light cupula is still not clear, and the treatment modality for this disease needs further investigation.