Dong-Han Lee; Chang-Hee Kim

doi:10.21790/rvs.2025.002

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Review Article
Persistent geotropic direction-changing positional nystagmus: a systematic review: Dong-Han Lee^1,2, Chang-Hee Kim^1,2; Research in Vestibular Science 2025;24(3):153-176.
DOI: https://doi.org/10.21790/rvs.2025.002
Published online: September 15, 2025

¹Department of Otorhinolaryngology-Head and Neck Surgery, Konkuk University Medical Center, Seoul, Korea

²Research Institute of Medical Science, Konkuk University School of Medicine, Seoul, Korea

Corresponding author: Chang-Hee Kim Department of Otorhinolaryngology-Head and Neck Surgery, Konkuk University Medical Center, Konkuk University School of Medicine, 120-1 Neungdong-ro, Gwangjin-gu, Seoul 05030, Korea. E-mail: changhee.kim@kuh.ac.kr

• Received: January 22, 2025 • Revised: June 7, 2025 • Accepted: June 10, 2025

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Abstract
INTRODUCTION
METHODS
MAIN TEXT
Treatments
CONCLUSIONS
ARTICLE INFORMATION
REFERENCES

Abstract

Persistent geotropic direction-changing positional nystagmus (DCPN) is a unique clinical phenomenon characterized by persistent nystagmus observed during the supine head roll test. Unlike other DCPNs caused by canalolithiasis or cupulolithiasis, this persistent geotropic form is not fully explained by conventional mechanisms. The “light cupula” hypothesis, introduced in the early 2000s, proposes that reduced cupula density relative to the surrounding endolymph is a key explanation for cases of peripheral origin. However, other mechanisms, such as heavier endolymph, light debris, utricular dysfunction, and perilymph-endolymph density difference have also been suggested. Persistent geotropic DCPN may also arise from central lesions, further complicating its diagnosis. This review examines persistent geotropic DCPN with a focus on the peripheral hypothesis, particularly the concept of the light cupula, exploring its origin, clinical characteristics, diagnostic approaches, proposed alternative mechanisms, and treatment. This review also explores cases of persistent geotropic DCPN linked to central lesions and coexisting conditions like vestibular migraine and Ménière disease, focusing on their distinctive characteristics as reported in the literature. The limited effectiveness of available treatments highlights the importance of advancing research to better understand and manage this condition.
Keywords: Benign paroxysmal positional vertigo; Dizziness; Positional nystagmus; Vestibular diseases; Semicircular canals

INTRODUCTION

Direction-changing positional nystagmus (DCPN), characterized by shifts in nystagmus direction with different head positions, is a key diagnostic feature of benign paroxysmal positional vertigo (BPPV) in the horizontal semicircular canal (HC). The supine head roll test, in which the patient lies supine with the head elevated approximately 30° to align the HC plane with the gravitational vector, is the primary diagnostic method. This test reveals two main nystagmus patterns: (1) geotropic, beating toward the ground when the head is turned to either side or (2) apogeotropic, beating away from the ground [1].

In HC canalolithiasis, free-floating otoconial debris within the canal is known to cause either geotropic or apogeotropic nystagmus, depending on the debris location. Debris in the posterior arm induces geotropic DCPN, while debris in the anterior arm leads to apogeotropic DCPN [2]. Following head movement, the displaced debris creates endolymphatic flow, deflecting the cupula and producing nystagmus after a brief latency period. This latency can be explained by the otoconia’s initial slow movement, gradual acceleration, and interaction with the canal wall [3]. This ‘transient’ nystagmus typically resolves within 30 seconds to 1 minute as the debris settles at the gravitational low point. However, it is noteworthy that when the healthy ear is down, debris in the anterior arm may settle near the canal side of the cupula, potentially leading to sustained ampullopetal deflection and persistent nystagmus [4]. In contrast, HC cupulolithiasis, caused by otoconial debris adhering to the cupula, leads to immediate nystagmus due to direct cupula deflection by gravity. This nystagmus is ‘persistent,’ apogeotropic, and lasts over 1 minute, with a shorter or negligible latency compared to canalolithiasis (Table 1).

However, there are cases of persistent geotropic DCPN observed during the supine head roll test that are not adequately explained by the mechanisms of canalolithiasis or cupulolithiasis. This distinctive pattern of nystagmus has led to the hypothesis of the “light cupula” phenomenon, where the HC cupula’s density becomes lower than the surrounding endolymph, causing persistent deflection against gravity. Light cupula is one hypothesized peripheral mechanism of persistent geotropic DCPN, but the two terms are not interchangeable. Persistent geotropic DCPN describes a clinical manifestation, whereas light cupula refers to a specific proposed mechanism. Furthermore, persistent geotropic DCPN can also arise from central lesions, complicating its diagnosis.

Given these complexities, clarifying the distinction between persistent geotropic DCPN and light cupula is essential for diagnostic accuracy and clear communication among clinicians and researchers. However, in the field of medicine, it is often observed for terms originally describing mechanisms to evolve into widely accepted labels for specific conditions. Considering the widespread use of “light cupula” to explain persistent geotropic DCPN of peripheral origin, this review adopts the term as a practical label for such cases, while recognizing it as one of several potential mechanisms. Similarly, persistent apogeotropic DCPN is often explained using the term ‘heavy cupula,’ a condition where the cupula’s density is higher than that of surrounding endolymph. Cupulolithiasis—otoconial particles attaching to the cupula—is one of the possible causes.

This review aims to provide a comprehensive understanding of persistent geotropic DCPN by examining the historical background, clinical characteristics, proposed mechanisms, diagnostic considerations, and treatment strategies of light cupula phenomenon, as well as cases arising from comorbid conditions and central lesions. This review is based in part on our previously published works: a Korean-language review article [5] and a prior English-language review [6]. In the present paper, we have updated and expanded the content to incorporate newly published evidence and provide a more comprehensive overview of the topic.

METHODS

This review examined studies on persistent geotropic DCPN and related conditions, such as light cupula and positional alcohol nystagmus (PAN), published from the 1950s to May 2025. A PubMed search was conducted using the keywords “persistent geotropic” (n=90), “light cupula” (n=86), and “positional alcohol nystagmus” (n=68), yielding a total of 244 articles. After removing 42 duplicates, 202 articles were screened by title and abstract. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for the study selection process. Inclusion criteria were: (1) relevance to persistent geotropic DCPN or related conditions, (2) human, animal, or experimental studies, (3) peer-reviewed full-text in English, and (4) original studies or reviews with analyzable data or meaningful insights. Exclusion criteria included non-English publications, unrelated topics, and unavailable full texts. Additional articles were included through reference searches. In a few cases where full-text access was not available, frequently cited studies from multiple prior publications in the field were selectively included based on their relevance and influence. Final citations were carefully selected to minimize redundancy and to highlight studies offering distinct clinical and pathophysiological insights. The selection process is summarized in the PRISMA flowchart (Fig. 1).

MAIN TEXT

Persistent Geotropic Direction-Changing Positional Nystagmus of Peripheral Origin: the Concept of ‘Light Cupula’

The concept of light cupula originated from studies on PAN, first described by Aschan et al. in 1956 [7]. Subsequent research by Money et al. in 1965 and 1974 [8,9] detailed the mechanism behind PAN. After alcohol consumption, ethanol (specific gravity, 0.79) diffuses more rapidly into the cupula than the endolymph, temporarily reducing its density and causing persistent geotropic DCPN (PAN-I) (Fig. 2). Conversely, as blood alcohol levels decline, ethanol is cleared faster from the cupula than the endolymph, making the cupula heavier and resulting in persistent apogeotropic DCPN (PAN-II). Aschan et al. [7] demonstrated in 1956 that PAN-I or PAN-II could persist for up to 6 hours.

In 2001, Shigeno et al. [10] introduced the concept of “light cupula”. In 2004, Hiruma and Numata [11] identified a neutral point in patients with persistent DCPN, where nystagmus disappeared when the head was turned 20° to 30° from the supine position and rotated 180° from that point. They suggested that this phenomenon could be adequately explained by the assumption of either a light or heavy cupula. In 2011 and 2013, Tomanovic and Bergenius [12,13] reported that the nystagmus patterns observed in hemilabyrinthectomized patients during PAN-I and PAN-II closely resembled those found in patients with light cupula and HC cupulolithiasis, respectively. Subsequent case reports of light and heavy cupulas by Kim et al. [14] in 2015 and Ichijo [15] in 2016 further expanded interest in the concept. Recently, Peng et al. [16] described 189 light cupula cases in 2023, and Qin et al. [17] added 85 cases in 2024, further providing valuable data on this phenomenon.

Clinical Features and Diagnosis of Patients with Light Cupula

Diagnostic approach: supine head roll test

The key symptom of light cupula is vertigo triggered by head position changes, with persistent geotropic DCPN during the supine head roll test serving as a characteristic diagnostic feature. This phenomenon is explained by the lower density of the cupula compared to the surrounding endolymph, causing continuous deflection of the cupula against gravity (Fig. 3). Conversely, a “heavy cupula,” with greater density than the endolymph, produces an opposite deflection. In HC cupulolithiasis, otoconial debris adheres to the cupula, creating a heavy cupula state. Both light and heavy cupula conditions result in persistent DCPN (geotropic and apogeotropic, respectively), characterized by shorter latency compared to transient DCPN and prolonged nystagmus lasting over 1 minute.

Therefore, although observing nystagmus for more than 1 minute during the supine head roll test is recommended, Okazaki et al. [18] reported in 2017 that a 30-second observation period was sufficient to distinguish persistent geotropic DCPN, achieving a sensitivity of 82% to 100% and a specificity of 81% to 100%, considering potential patient discomfort during the examination.

Null point

The null point, where vertigo and nystagmus disappear during head turning in the supine head roll test, was described by Bisdorff and Debatisse [19] in 2001 as part of their observations on HC cupulolithiasis. They also identified a null point in the pitch plane, further highlighting the gravity-sensitive nature of the HC and its alignment with the gravitational vector.

Similarly, in light cupula, the null point is a key clinical feature and serves as an important diagnostic indicator during the supine head roll test. Understanding the null point requires knowledge of the anatomical orientation of the HC and the cupula axis within the temporal bone. Historically, there have been misconceptions and revisions regarding this anatomy [12,20], but current understanding indicates that the anterior portion of the HC is inclined upward by approximately 30° relative to the horizontal plane. Additionally, the axis of the cupula aligns anteroposteriorly outward by about 20° to 30° relative to the sagittal plane, with the upper part of the cupula closely adhering to the canal wall (Fig. 4) [14,21-23]. When the head is rotated 20° to 30° toward the affected side during the supine head roll test, the cupula axis aligns parallel to the gravitational vector. This alignment eliminates cupula deflection, causing vertigo and nystagmus to cease at the null point, with nystagmus direction reversing on either side (Fig. 3). In this review, we adopt and describe the most widely accepted cupula axis as mentioned above. However, the anatomical orientation of the cupula axis still remains a topic of debate due to limited case data and insufficient knowledge about its variations [24,25]. For example, Curthoys et al. [26] suggested in 2009 that the cupula axis is nearly parallel to the median plane of the head. According to their speculations, deviations toward the ipsilateral anterior or posterior semicircular canals may fall within normal anatomical variations.

The null point has been reported across various ranges in different studies: 0°–30° (Tomanovic and Bergenius [25]), 20°–60° (Ichijo [27]), 5°–85° with a mean of 44.4°±20.5° (Ichijo [15]), 15°–58° with a mean of 25.4°±12.5° (Hiruma et al. [28]), 25.7°±9.3° (Tang et al. [29]), and interquartile range (IQR) of 22.5°–45° with a median 30° (Song et al. [30]). The wide range of reported null point angles appears too large to be explained solely by anatomical variations in the cupula axis. In 2016, Ichijo [15] found that the null point angle was larger in light cupula than in heavy cupula. He suggested that light debris may more commonly attach to the canal side of the HC cupula than to the utricular side, requiring additional head rotation beyond the position where the cupula axis aligns parallel to gravity to eliminate hair cell stimulation. Another possibility is that this null point angle variability is influenced by pathological conditions, such as increased endolymphatic fluid volume, which could alter the orientation of the cupula axis [25].

Considering the above discussions, determining the affected side based on the null point’s direction remains debatable [12,20,24,25,31]. In patients with light cupula accompanied by inner ear disorders, the affected side is likely to correspond to the side of the inner ear disorder. However, there have been reports indicating that the direction of the null point observed during the head roll test does not always align with the side of the inner ear disorder [24,32]. Nevertheless, most researchers accept the observed direction of the null point as a primary indicator of the affected side [1,14-16,27,33-42].

Although the PAN phenomenon inspired the concept of light cupula, it differs from unilateral light cupula when viewed from a null point perspective. In unilateral light or heavy cupula, the HC cupula on the unaffected side maintains a density equal to the surrounding endolymph and is unaffected by gravity. In contrast, PAN or bilaterally symmetric light cupula involves simultaneous density changes in the cupulae on both sides, making both subject to gravity. This symmetry is expected to cancel out gravitational effects in supine or prone positions, resulting in an absence of nystagmus (Fig. 2).

Bow and lean test

In 2015, Kim et al. [14] suggested the bow and lean test as an alternative method for assessing persistent DCPN (Fig. 4). In the upright sitting position, the HCs are inclined forward by approximately 30°. In patients with a light cupula, this inclination causes the affected-side cupula to bend ampullofugally, inducing nystagmus beating toward the contralesional side (Fig. 4F). Slightly bowing the head aligns the HC parallel to the ground, where the first null point is observed (Fig. 4E).

Leaning the head back in a sitting position mimics the supine head roll test position, aligning the HC plane parallel to gravity (Fig. 4C). In this position, turning the head side to side produces persistent geotropic DCPN in light cupula cases and persistent apogeotropic DCPN in heavy cupula cases (Fig. 4A, D). A second null point occurs when the head is slightly turned toward the affected side (Fig. 4B).

Similarly, in the bowing position, turning the head side to side generates persistent geotropic DCPN in light cupula cases and persistent apogeotropic DCPN in heavy cupula cases (Fig. 4I, G, J). A third null point is observed when the head is slightly turned toward the affected side while bowing (Fig. 4H).

Additionally, in light cupula cases, bowing the head induces nystagmus beating toward the affected side (Fig. 4I), while leaning the head backward produces nystagmus beating toward the unaffected side (Fig. 4C). In contrast, heavy cupula cases show the opposite pattern: bowing induces nystagmus beating toward the unaffected side, and leaning induces nystagmus beating toward the affected side.

Theoretical and observed nystagmus patterns in light and heavy cupula

Assuming a light or heavy cupula, persistent DCPN theoretically occurs in all positions except at the null points. For example, nystagmus may be observed in both upright sitting and supine positions, aiding in the diagnosis and determination of the affected side. In a patient with a right-sided light cupula, left-beating nystagmus is observed in the supine position (Fig. 3A), whereas right-beating nystagmus occurs when the head is bent forward in a sitting position (bowing position, Fig. 4I).

During the supine head roll test, nystagmus intensity is stronger when turning the head toward the affected side (Fig. 3C, F), as head rotation toward the affected ear induces ampullopetal deviation, generating an excitatory response and stronger nystagmus. Conversely, rotation toward the healthy side causes ampullofugal deflection, producing a weaker inhibitory response, following Ewald’s second law [1,43].

However, not all patients exhibit these theoretically expected patterns. While spontaneous nystagmus in the sitting position is indeed more common in light cupula than canalolithiasis, it is not always observed [41]. Qin et al. [17] reported that over 80% of light cupula patients showed nystagmus in supine, bowing, and leaning positions, but only about 60% showed spontaneous nystagmus.

Studies indicate that identifying the affected side by bow and lean nystagmus direction provides comparable accuracy to the null point method [17,35], whereas relying on stronger DCPN intensity yields lower accuracy rates (e.g., Kim et al. [1], 68%; Kim et al. [35], 100%; Seo et al. [37], 67%; Qin et al. [17], 64%; Kim et al. [24], 16%). Kim et al. [24] and Qin et al. [17] suggested that differing degrees of cupula deflection during the supine roll test complicate nystagmus intensity comparisons. For example, in a right-sided light cupula case, Ewald’s second law predicts that equal cupula deflections during rightward and leftward head rotations would produce stronger nystagmus during rightward rotation due to excitation. However, if the head rotation angles from the supine null position—θ1 for rightward and θ2 for leftward—are unequal, the resulting asymmetry in cupula deflection prevents a straightforward application of Ewald’s second law, leading to observed nystagmus that may deviate from theoretical predictions (Fig. 5). In 2015, Shin and Kim [44] also proposed several mechanisms to explain such discrepancies, including (1) incomplete head rotation to the affected side, (2) anatomical variations of the HC (e.g., excessive inclination of HC), (3) otolith organ influence on HC reflex via the velocity storage integrator, and (4) variations in the cupula’s anatomical orientation within the HC.

It is also possible that an insufficient density difference between the cupula and endolymph may allow detectable nystagmus only in positions that induce significant cupula deflection, or it may fail to produce noticeable intensity differences predicted by Ewald’s second law [25,45]. In this context, Hong et al. [41] reported lower slow-phase velocity (SPV) values in light cupula patients than in canalolithiasis cases during the supine roll test, suggesting a potential upper limit to SPV in persistent geotropic DCPN. However, conflicting results have also been reported in other studies [46]. Biomechanical effects, such as changes in the density and viscosity of the endolymph, can influence the intensity of nystagmus [47]. Additionally, affected-side caloric paresis, often observed in light cupula cases, may be associated with the intensity and occurrence of nystagmus [25,48]. Furthermore, anatomical or morphological changes in the cupula, as well as pathological process like increased endolymphatic fluid volume, might alter the orientation of the cupula axis, potentially resulting in nystagmus patterns that deviate from theoretical expectations [25]. Lastly, in positions where the cupula is deflected, central adaptation during sustained head positioning can cause nystagmus to attenuate, potentially leading to absence of nystagmus and confusion with the null point [45].

Latency and fatigability

It is generally accepted that nystagmus latency is shorter in cupulopathy than in canalolithiasis, with canalolithiasis typically exhibiting a latency of a few seconds [49]. However, even in canalolithiasis, large otoconial aggregates can settle faster than smaller particles, resulting in shorter nystagmus latency, similar to light cupula cases. Conversely, smaller particles or those with significant interaction with the canal wall may settle more slowly, leading to prolonged responses. These biomechanical differences in particle behavior highlight the variability in positional nystagmus characteristics [46,50]. Quantitative analysis of nystagmus latency and duration in patients with canalolithiasis and cupulopathy remains limited, with large-scale studies being particularly scarce. However, a 2019 study by Wang et al. [43] comparing HC canalolithiasis, HC-heavy cupula, and HC-light cupula reported no statistically significant differences in nystagmus onset latency among the three groups. Notably, the duration of nystagmus was markedly longer in HC-heavy and HC-light cupula compared to HC canalolithiasis, and the time to reach 63% of peak SPV (time constant) was also markedly longer in the cupulopathy groups (23.1–24.4 seconds vs. 5.4 seconds). Despite these temporal differences, peak SPV intensity did not differ significantly among the groups. These findings suggest that HC-heavy and HC-light cupula share similar temporal characteristics and likely stem from a common pathophysiological mechanism of cupulopathy, while differing substantially from canalolithiasis.

Quantitative analysis of nystagmus characteristics in canalolithiasis and cupulopathy faces several challenges during the supine head roll test. If nystagmus is already present in the supine position, turning the head toward the direction that intensifies the nystagmus may result in negligible latency. Conversely, turning the head toward the direction that reverses nystagmus may involve a pause before the direction changes, leading to longer latency. Furthermore, the gradual build-up of nystagmus complicates pinpointing the exact onset, adding ambiguity to latency determination.

In the context of paroxysmal positional nystagmus, fatigability is defined as a decrease in nystagmus with repeated positioning [51]. This phenomenon can be explained by the dispersion of clustered otoconial debris due to repeated head movements, rendering the debris less effective in inducing nystagmus. Fatigability of nystagmus is known as a characteristic of canalolithiasis, not cupulopathy. Some studies have reported the fatigability of nystagmus in light cupula cases [38,43]. However, these studies actually describe the gradual attenuation of nystagmus intensity after reaching its peak during a single positioning, which should not be misunderstood as true fatigability. While the crescendo-decrescendo pattern of nystagmus has long been described as a characteristic of canalolithiasis, the above-mentioned study described it in both canalolithiasis and cupulopathy; the difference is that the time constant is significantly longer in the latter. In cupulopathy, the gradual decline in intensity after the peak is thought to result from central adaptation within the vestibular system [43,52]. Further large-scale quantitative studies focusing on transient and persistent DCPN are necessary to better define nystagmus characteristics and explore underlying mechanisms.

Light cupula in vertical semicircular canals

Several studies have noted vertical and torsional components with horizontal nystagmus in light cupula patients, suggesting that vertical semicircular canals on the affected side may be involved [53,54]. According to a 2016 study by Kim et al. [32], among 28 patients with persistent geotropic DCPN associated with sudden sensorineural hearing loss (SSNHL), five showed positive responses on the Dix-Hallpike test, suggesting possible involvement of the vertical semicircular canals. In the same year, Ichimura and Otsuka [55] reported a case of posterior canal light cupula and speculated its rarity might be due to the difficulty of buoyant light debris sinking into the ampulla of the posterior canal, which is positioned lower in supine or sitting positions, if the light cupula mechanism involves light debris. Tomanovic and Büki [45] also demonstrated in 2016 that persistent vertical nystagmus, including upbeat and downbeat types, can be induced by symmetrical positioning in the pitch plane after alcohol ingestion, likely due to activation or inhibition of the vertical semicircular canals.

Additionally, Kim et al. [56] described in 2023 the presence of a null point in the pitch plane among patients showing persistent torsional-upbeating nystagmus during the Dix-Hallpike position, suggesting that cases previously considered as posterior canal cupulolithiasis may actually be due to a light cupula condition of ipsilateral posterior or contralateral anterior canal. These findings indicate that light cupula is not limited to the HCs. Accordingly, the Dix–Hallpike test should be considered essential in evaluating patients with suspected light cupula, especially when vertical or torsional nystagmus is present. Moreover, further studies are needed to clarify the anatomical orientation of the cupula axis within the vertical semicircular canals to better understand the presence or absence of vertical and torsional components in light cupula-associated nystagmus.

Audiometric and vestibular function tests

Pure tone audiometry

Hearing test results in light cupula patients have been reported in a few case studies, but analyses involving a large number of patients are limited. Tang et al. [29] reported in 2019 that no significant abnormalities were observed in the audiometric tests of nine patients with light cupula. In contrast, Si et al. [57] reported in 2021 ipsilateral hearing loss in three out of 30 patients with persistent geotropic DCPN.

Additionally, a study on SSNHL patients with positional nystagmus (n=44) revealed that 52% (23 of 44) exhibited persistent geotropic DCPN without abnormal findings on the Dix-Hallpike test. Among these, 13 (57%) had profound hearing loss, followed by high-tone hearing loss in five patients (22%) and flat-type hearing loss in five patients (22%); interestingly, no cases of low-tone hearing loss were observed [32]. These findings suggest a notable association between SSNHL and persistent geotropic DCPN, emphasizing the importance of evaluating auditory function in patients presenting with persistent geotropic DCPN.

Positional pure tone audiometry

In 2020, Lee et al. [34] hypothesized that in patients with light cupula, the tectorial membrane, known as the cochlear counterpart of the cupula, might also be influenced by head position in the gravity plane, given the circulation of endolymph within the endolymphatic membrane between the cochlea and vestibular organs. However, their study measuring pure tone audiometry thresholds in 12 unilateral light cupula patients across three head positions (upright, cochlear apex-up, and cochlear apex-down) showed no significant change in hearing thresholds according to head position. From these observations, they concluded the following: (1) the phenomenon of heavier endolymph is confined to the vestibular end organs, excluding the cochlea; (2) the light cupula phenomenon is more likely to result from a light debris rather than a heavier endolymph or lighter cupula; and (3) the effects of light cupula could be modulated by outer hair cells, which perform fine-tuning within the cochlea, even in the presence of a lighter tectorial membrane or heavier endolymph.

Caloric test and video head impulse test

Caloric paresis in light cupula cases is reported to occur in 20%–65% of patients, primarily on the affected side. In 2024, Qin et al. [17] reported that, among 70 patients who underwent caloric testing, 37 (52.9%) showed abnormal canal paresis (CP, >25%), and 31 (44.3%) had abnormalities on the lesion side. Similarly, Si et al. [57] found in 2021 abnormal CP in 13 of 30 patients (43.3%), with 8 (26.7%) showing lesion-side abnormalities. In 2014, Tomanovic and Bergenius [25] observed lesion-side abnormalities in 13 of 20 patients (65%; CP ≥20%). In smaller cohorts, Ichijo [27] identified lesion-side abnormalities (CP >25%) in three of 14 patients (21.4%) in 2016, while Tang et al. [29] reported lesion-side abnormalities in two of 10 patients (20%) in 2019.

In a 2016 study by Kim et al. [32], among 22 patients with persistent geotropic DCPN and SSNHL, 14 (64%) had abnormal CP (≥25%) and 13 (57%) showed positive results on the horizontal head impulse test. Notably, one patient had contralesional CP, possibly due to excitation of vestibular function on the affected side.

Although caloric paresis is frequently observed in BPPV [58], it appears more frequently in light cupula. In a 2025 study by Bae et al. [59], 61.8% of patients (21 of 34) with persistent geotropic DCPN showed abnormal CP (≥25%), compared to 22.5% (9 of 40) in persistent apogeotropic and 11.1% (3 of 27) in transient geotropic types (p=0.001 and p<0.001). The persistent geotropic DCPN group also had the highest median CP value (26.0%), compared to 14.5% in persistent apogeotropic and 7.0% in transient geotropic group. Additionally, 52.9% of patients (18 of 34) in the persistent geotropic group showed lesion-side caloric paresis.

In contrast to the findings of Kim et al. [32] in 2016, all patients—including those with persistent geotropic DCPN—in the 2025 study of Bae et al. [59] showed normal video head impulse test (vHIT) results. This discrepancy may stem from the exclusion of patients with acute sensorineural hearing loss in Bae et al.’s study [59], whereas Kim et al.’s cohort [32] included individuals with underlying cochlear injury. Such injury may have been associated with more widespread vestibular involvement, leading to a higher rate of vHIT abnormalities. The strict exclusion criteria (e.g., excluding patients with migraine and acute sensorineural hearing loss) and same-day caloric testing at the time of positional nystagmus observation in the study of Bae et al. [59] provide valuable insights, though caution is needed when comparing with studies using different protocols. Interestingly, Song et al. [30] studied 51 patients with light cupula in 2024 using similar criteria and reported a higher incidence of corrective saccades in the affected HC despite normal vHIT gain. Although Bae et al. [59] stated that catch-up saccades of vHIT were evaluated, the absence of detailed results limits direct comparison and highlights the need for further investigation. While sporadic vHIT abnormalities have been reported in BPPV, they are not known to correlate clearly with the affected semicircular canal [30]. Compared to the HC cupulolithiasis group, the light cupula group showed a significantly higher vHIT abnormality rate, suggesting fundamental pathophysiological differences between the two conditions [30]. Notably, even with normal gain, frequent corrective saccades may indicate subtle vestibulo-ocular reflex (VOR) pathway impairment and reduced dynamic visual acuity. This may be attributed to a reduction in the density of crista ampullaris, leading to decreased response to high-frequency VOR stimulation.

There is speculation that CP in light cupula may result from central inhibition during vestibular compensation, where the cerebellum suppresses the vestibular nucleus, rather than from direct sensory organ damage [60]. Additionally, morphological changes in the cupula and altered endolymph dynamics have also been proposed as contributing factors, although the exact mechanism remains unclear [25,48]. The 2025 study by Bae et al. [59] provides valuable data for further discussion on these mechanisms. In follow-up testing, CP values are often normalized after the resolution of positional nystagmus, suggesting a transient dysfunction possibly caused by reversible changes in cupula properties or endolymph composition rather than permanent vestibular injury. The authors hypothesized that the cupula buoyancy could offset the thermal buoyancy of the endolymph during warm irrigation. They also speculated that pre-existing CP might predispose individuals to persistent geotropic DCPN, or conversely, that the condition itself may result in persistent CP through sensory epithelium injury or cupula degeneration. Moreover, as thoughtfully discussed by the authors, changes in the thermal expansion coefficient of the endolymph may affect convection efficiency, and alterations in its viscosity could theoretically influence vHIT gain; however, the consistently normal vHIT findings observed in all patients do not support the latter explanation. Further investigation is needed to clarify the underlying mechanisms.

Vestibular evoked myogenic potential

Studies examining vestibular evoked myogenic potential (VEMP) outcomes in light cupula patients are limited [25,32,57]. In 2021, Si et al. [57] reported abnormal cervical VEMP (cVEMP) results in six out of 30 patients with light cupula. In a 2014 study of Tomanovic and Bergenius [25], pathological findings were observed in cVEMP in two out of 13 patients and in ocular VEMP in five out of nine patients, suggesting that the lower branch of the vestibular nerve and/or the saccule may not be the primary lesion sites. Another study mentioning VEMP responses in a subset of light cupula cases with SSNHL found no measurable responses on the affected side, likely suggesting otolith organ dysfunction [32].

Subjective visual horizontal and subjective visual vertical

In 2014, Tomanovic and Bergenius [25] reported that approximately 60% of patients (10 of 17) with light cupula exhibited subjective visual horizontal abnormalities, with tilting to the affected side, indicating otolithic dysfunction.

In contrast, a 2014 study by Kim et al. [61] involving 17 patients with simultaneous SSNHL and persistent geotropic DCPN found that 29% (5 of 17) of patients showed abnormal static subjective visual vertical (SVV), with tilting predominantly toward the contralesional side (80%, 4 of 5).

According to the study by Shigeno [62] in 2023, which measured static SVV in patients with DCPN involving horizontal canal, the severity of otolithic dysfunction varied among DCPN subtypes, with the most pronounced utricular dysfunction observed in light cupula cases. The order of dysfunction severity was as follows: light cupula > cupulolithiasis > geotropic and apogeotropic canalolithiasis, suggesting differing levels of utricular involvement by DCPN subtype.

Diagnostic criteria

Based on the features outlined above, the diagnosis of unilateral light cupula of the HC can be made using the following key criteria: (1) persistent geotropic DCPN lasting over one minute during the supine head roll test, with minimal latency and no fatigability on repetition; (2) identifiable null point corresponding to the affected side; (3) absence of central nervous system abnormalities [1,15,17,36,63,64].

To accurately diagnose light cupula, it is essential to satisfy all of these criteria, as nystagmus duration alone may not be sufficient. In cases of canalolithiasis, for example, the relatively short duration of nystagmus is thought to result not from hair cell fatigue but from the time required for otoconial debris to settle at the lowest gravitational point [38]. If a large number of otoconial debris are present or if a stenosis exists within the canal, this duration may be prolonged beyond one minute due to an ‘hourglass effect’ caused by the slowed flow of otoconial debris. Differentiating light cupula from central disorders is crucial, as prolonged geotropic DCPN can also be observed in central conditions [65]. However, the persistent absence of neurologic signs and eventual complete remission strongly support a benign, peripheral etiology. As understanding evolves, diagnostic criteria may be further refined.

Epidemiological patterns and natural course

In 2014, Kim et al. [1] reported that among 388 patients with BPPV observed over approximately 1.5 years, the incidence of light cupula was 4.9%. Within DCPN cases, the incidence was 9.4%, and among geotropic DCPN cases specifically, it reached 14.2%. Additionally, the natural course of light cupula appears to be longer than that of HC BPPV. In 2018, Kim et al. [66] tracked 65 patients with persistent geotropic DCPN and found no significant difference in the time required for nystagmus resolution or symptom improvement between the treated (n=35) and untreated (n=30) groups. The average duration from diagnosis to nystagmus resolution was around 8 days, notably longer than the typical natural course reported for HC BPPV, which is 4.7±3.9 days for canalolithiasis and 4.4±5.0 days for cupulolithiasis [66,67]. Bae et al. [59] also reported in 2025 a median disease duration (from symptom onset to nystagmus resolution) of 23.0 days (IQR, 41.0) in patients with persistent geotropic DCPN, which was significantly longer than that observed in persistent apogeotropic (8.0 days; IQR, 27.0) or transient geotropic DCPN (9.0 days; IQR, 35.0) (p=0.005). According to studies, 60%–70% of patients show improvement after 1 week, with nearly 90% showing recovery within a month [16,37]. Considering its recent recognition and limited knowledge, light cupula may be underdiagnosed or misclassified as other BPPV types, highlighting the need for further research to better understand its prevalence and characteristics.

Right-to-left ratio

Studies report varying right-to-left lesion involvement ratios in light cupula cases: Kim et al. [1] found a 13:6 ratio in 19 patients; Ichijo [15], 22:11 in 33 patients; Ban et al. [64], 16:14 in 30 patients, Seo et al. [37], 17:10 in 27 patients; Hong et al. [41], 29:20 in 49 patients; Yetiser and Ince [46], 8:10 in 18 patients; Peng et al. [16], 97:92 in 189 patients; Qin et al. [17], 47:38 in 85 patients; and Song et al. [30], 25:26 in 51 patients. At first glance, these data suggest a possibility of right-side predominance. In 2004, von Brevern et al. [68] reported that BPPV affects the right labyrinth 1.41 times more frequently than the left. They speculated that this trend could be due to the common habit of sleeping on the right side, which may reduce discomfort from perceiving heartbeats on the left [68,69]. A 2022 study by Shigeno et al. [70] found that patients with light cupula more often slept on the affected-ear-down side, supporting a possible link between sleep posture and lesion side. However, no significant right-left dominance was observed (48 right, 45 left), suggesting other factors may be involved. Further research is required to confirm whether right-side predominance exists in light cupula cases and to explore its mechanisms.

Light cupula cases involving both HCs symmetrically might theoretically mimic PAN-I, where nystagmus disappears in supine or prone positions, complicating the identification of a clear null point on either side. Although such simultaneous bilateral cases are rarely reported [1,71], they might be underreported due to diagnostic challenges and subtle clinical presentations. In other words, the frequent observation of apparently unilateral cases may not necessarily reflect truly one-sided pathology. Bilateral involvement may be more common than recognized, but with subtle asymmetry in cupula density or deflection between sides. Such asymmetry could cause a lateral shift in the null point, resulting in a clinical presentation that appears unilateral. From this perspective, the variability in observed null point angles might not solely reflect the anatomical orientation of a unilateral cupula axis, but also the degree of asymmetry in bilateral involvement. Moreover, current diagnostic criteria that require a clearly identifiable null point on one side may contribute to the underrecognition of bilateral cases. Future studies comparing null point angles and their variability between patients with and without unilateral inner ear pathology could provide further insight into this possibility. Additionally, there are documented cases of recurrent light cupula affecting each side alternately over time [16,44].

Female-to-male ratio

Furthermore, light cupula has been consistently reported as more common in women than men. The female-to-male ratios across studies are: Kim et al. [1], 14:5 in 19 patients (mean age, 55 years; range, 35–75 years); Tomanovic and Bergenius [25], 13:7 in 20 patients (mean age, 53 years; range, 21–83 years); Ichijo [15], 23:10 in 33 patients (mean age, 60.9 years); Ban et al. [64], 20:10 in 30 patients (mean age, 54±13.8 years; range, 30–74 years); Seo et al. [37], 14:13 in 27 patients (aged 36–80 years); Hong et al. [41], 32:17 in 49 patients (mean age, 50±13.1 years; range, 26–76 years); Kim et al. [24], 17:8 in 25 patients (mean age, 54.1 years); Si et al. [57], 19:11 in 30 patients (mean age, 51±14.9 years); Yetiser and Ince [46], 8:10 in 18 patients (mean age, 48.5±9.41 years); Peng et al. [16], 134:55 in 189 patients (mean age, 56±14.7 years); Qin et al. [17], 68:17 in 85 patients (mean age, 61±11.9 years; range, 14–81 years); Song et al. [30], 42:9 in 51 patients (mean age, 55.4±13.9 years); Chang et al. [72], 22:11 in 33 patients (mean age, 65.4 years; range, 44–83 years); and Bae et al. [59], 26:8 in 34 patients (median age, 57.5 years; IQR, 18.8 years). BPPV is also widely observed to have a higher incidence in females than in males [73]. Several factors, including hormonal influences, age, osteoporosis, migraines, and head trauma, are thought to contribute to BPPV occurrence [74-76]. As will be discussed in the following section, if the light cupula phenomenon arises through mechanisms distinct from those of traditional BPPV, further investigation may be necessary to fully explain its higher prevalence in women.

Recurrence rate

The recurrence rate of light cupula cases appears higher than that of canalolithiasis or cupulolithiasis [39], with studies reporting varied rates, including 33% in 27 cases [37], 72.3% in 34 cases [39], 33% in 18 cases [46], and 17% in 189 cases [16]. These differences may be influenced by patients’ perceptions of severity and follow-up protocols. As a related finding, more than one recurrence has been observed in some patients [39], and recurrence rates are reported to be higher in women [1]. According to Ichijo’s 2020 findings [39], patients with light cupula exhibited a high recurrence of the same subtype, leading to the speculation that these patients may have a predisposition to produce light debris.

Proposed Mechanisms for Persistent Geotropic Direction-Changing Positional Nystagmus of Peripheral Origin

The exact etiology of light cupula is unclear, but vestibular system involvement is widely suspected [29,77]. The following hypotheses have been suggested to explain this phenomenon.

Lighter cupula theory

The lighter cupula theory proposes that light cupula results from a reduced density of the cupula compared to the surrounding endolymph within the semicircular canal. This mechanism is linked to PAN-I [8]. For example, in right-sided light cupula, positioning the right ear downward generates buoyancy acting on the cupula due to its lower density relative to the endolymph. This buoyancy deflects the stereocilia toward the kinocilium, causing excitation of the right HC. Conversely, positioning the left ear downward results in an inhibitory response as the buoyancy deflects the stereocilia away from the kinocilium, leading to geotropic nystagmus in both positions (Fig. 3).

Experimental evidence supports this theory. In 1974, Money and Myles [9] demonstrated that ingesting heavy water (deuterium oxide) induced heavy cupula conditions. Similarly, Shigeno et al. [78] replicated in 1989 persistent geotropic or apogeotropic DCPN in animal models by injecting low- or high-density solutions into the middle ear. Histological findings showed eosinophilic material near the round window membrane and the cupula, suggesting that the material diffused through the round window into the inner ear and altered the cupula’s density. In 1965, Money et al. [8] examined whether PAN occurred after alcohol administration in cats with specific semicircular canals removed by labyrinthectomy or inactivated by plugging. When the head was positioned upward or downward, alcohol-induced effects on the paired canals were symmetrical, thereby canceling out excitation or inhibition and preventing PAN. However, unilateral removal or inhibition of a semicircular canal resulted in horizontal PAN. When both HCs were inhibited, horizontal PAN was absent, but vertical and torsional components were still observed. In a 2011 study, Tomanovic and Bergenius [12] found that PAN did not occur in patients with bilateral labyrinthectomy, whereas unilateral labyrinthectomy induced PAN resembling a unilateral light cupula. Additionally, it has been suggested that sulfated proteoglycans found in the endolymphatic sac are synthesized in the cupula and released into the endolymph. In 2006, Bergenius and Tomanovic [20] hypothesized that disturbances in the homeostasis of these molecules could alter the relative density to the endolymph. In 2015, Seo et al. [79] reported a case of a patient with SSNHL and persistent geotropic DCPN lasting over 6 months, treated with HC plugging surgery. They suggested that intractable light cupula might result from irreversible morphological changes, such as cupula enlargement, which reduced its density while maintaining constant mass. Animal studies have shown the shrinkage of the cupula with gentamicin injection and enlargement of the cupula after disruption of the membranous labyrinth [48,80].

However, regarding the mechanism underlying the PAN phenomenon, which forms the basis of the lighter cupula theory, several issues arise that need clarification. While alcohol is known to cross the blood-brain barrier, it remains uncertain whether it can also cross the blood-perilymph barrier. Additionally, considering that the endolymphatic and perilymphatic spaces are strictly separated by tight junctions and structural barriers, and that the cupula is isolated from the apical surface of hair cells by the endolymph-filled subcupular space, it is necessary to explain how alcohol could diffuse directly into the cupula without first passing through the endolymph [33].

Heavier endolymph theory

This theory assumes that endolymph density may increase due to acute inner ear injury, such as from labyrinth hemorrhage, hypoperfusion, or inflammation [1]. Additionally, water-soluble macromolecules like proteoglycans in the endolymph may accumulate due to impaired endolymphatic sac function, leading to an increase in its specific gravity [1,81]. In 2011, Hiruma et al. [63] reported cases of patients who developed light cupula syndrome after a stellate ganglion block, suggesting that increased vertebral artery blood flow following the procedure might lead to inner ear hypoperfusion, causing changes in the density or viscosity of inner ear fluid. In 2014, Kim et al. [61] observed persistent geotropic DCPN in some patients with sudden hearing loss and vertigo, proposing that damage to the blood-labyrinth barrier could allow plasma proteins to leak into inner ear fluid, potentially raising the density of endolymph. In 2017, Choi et al. [71] reported a case of a 41-year-old patient with persistent geotropic DCPN following aseptic meningitis and elevated CSF protein levels, suggesting that the increased CSF protein may have altered perilymph composition, thereby supporting the “heavier endolymph” theory. Experimental studies have demonstrated changes in perilymph and endolymph composition following intravenous glycerol or intracisternal albumin or doxorubicin injections [82-84]. This hypothesis has been further supported by cases showing a transition between geotropic and apogeotropic DCPN over time, which was thought to result from overcompensation in endolymphatic homeostasis [53].

There are two primary criticisms regarding the ‘heavier endolymph’ theory: (1) the rapid onset of symptoms and short clinical course cannot be fully explained by changes in the specific gravity of the endolymph, and (2) in most cases of light cupula, only the HC is affected. However, in cases where light cupula is associated with conditions like sudden hearing loss [61] or meningitis [71], vertigo typically occurs hours to days after the onset of these symptoms, suggesting that the increase in vestibular endolymph density requires time. Furthermore, vertigo or nystagmus in light cupula cases generally resolves within 8 days to 2 weeks [1,66], significantly longer than the natural course of untreated HC canalolithiasis or cupulolithiasis [67].

Regarding the second criticism, since endolymphatic fluid circulates throughout the inner ear, connecting the three semicircular canals and otolith organs, it is reasonable to question why this phenomenon predominantly affects the HCs rather than all semicircular canals under ‘heavier endolymph’ condition. Similarly, the hypothesis that lighter or heavier cupula results from the diffusion of low- or high-density solutions into the cupula requires an explanation for its selective involvement of the HCs rather than the vertical ones [9]. While a recent case reported a light cupula involvement in all three semicircular canals on the affected side [54], most cases focus primarily on the HC. One speculation is that the predominance of horizontal nystagmus may result from the cancellation of vertical and torsional nystagmus components due to simultaneous excitation and inhibition of the vertical semicircular canals [1,54].

Another noteworthy perspective regarding vertical components of nystagmus in persistent geotropic DCPN suggests their potential origin from the HC itself [1,85]. Considering that eye movements occur in a plane parallel to the stimulated canal, the HC’s orientation at an 18.8° angle to the Reid horizontal plane suggests that when the HC is stimulated, the resulting eye movement axis is not perfectly perpendicular to the Reid horizontal plane. Consequently, it is natural for the induced nystagmus to include torsional components. Therefore, vertical components do not necessarily indicate vertical semicircular canal involvement, requiring caution in interpretation.

Meanwhile, the exact arrangement of the cupula within the vertical semicircular canals relative to gravity remains unclear and warrants further research. An animal study by Money et al. [8] in 1965 found that when bilateral HCs were inactivated, horizontal PAN was absent, while vertical and torsional components persisted. Based on these findings, Hiruma and Numata [11] speculated in 2004 that the vertical and torsional components of nystagmus in light cupula cases may be masked or hidden.

Light debris theory

The light debris theory hypothesizes that particles lighter than endolymph attach to the cupula of the HC, rendering the cupula lighter [15,20,77,85,86]. This theory is consistent with the predominance of horizontal nystagmus in light cupula cases, the sudden onset of positional vertigo, unilateral involvement, and the gradual improvement of symptoms over time. The theory also accounts for potential differences in clinical characteristics based on whether the light debris attaches to the utricular or canal side of the cupula. Proposed candidates for light debris include (1) degenerated inflammatory cells that swell and become lighter in the endolymph or (2) substances formed through chemical reactions involving otoconial debris [39,63,85,87-89].

In 2016, Ichijo [15] demonstrated that the null point angle is greater in light cupulas than in heavy cupulas, suggesting that light debris more frequently attaches to the canal side of the cupula. Additionally, the conversion of persistent apogeotropic to geotropic DCPN could be explained by the expansion and lightening of attached otoconial particles. Conversely, an increase in the density of attached light debris could raise the specific gravity of the cupula, potentially leading to the condition of a heavy cupula [53,90]. However, the hypothesis faces challenges, as treatments aimed at dislodging light debris have been largely unsuccessful [25,66], and the presence of light debris has yet to be conclusively confirmed. With regard to these criticisms, Ichijo’s explanation [91] (2017), based on animal studies showing that the cupula surface is sticky [3,92], is worth considering. He suggested that light debris is more difficult to overcome the adhesive force and detach compared to heavy debris [91].

Utricular dysfunction theory

In 2004, Hiruma et al. [11] identified persistent geotropic DCPN in patients with peripheral auditory-vestibular disorders and suggested utricular macula dysfunction as a potential underlying mechanism. However, this hypothesis has been challenged, as utricular macula dysfunction alone appears insufficient to explain such nystagmus [20].

In 2012, Imai et al. [93] described a unique case where a patient sequentially exhibited four types of nystagmus: posterior canal canalolithiasis, geotropic nystagmus with a long-time constant, HC cupulolithiasis, and HC canalolithiasis. They attributed these sequential changes to the migration of otoconial debris within the semicircular canals and suggested that geotropic nystagmus with a long time constant may result from denatured cupula or utricular imbalance caused by debris detachment, supporting the otolith imbalance hypothesis. However, this theory has limitations, as it does not explain the cessation of nystagmus in a neutral position, and no evidence directly links utricular dysfunction to horizontal eye movements [60]. In 2023, Ichijo and Teramoto [94] hypothesized that pathologic debris would remain in the utricle immediately after successful canalith repositioning in BPPV patients. To test this, they tilted the patients’ heads in various directions, aiming to directly stimulate the utricle with the debris. However, none of the patients exhibited nystagmus or dizziness, leading to the conclusion that otolith organ stimulation alone does not induce nystagmus.

Density difference between perilymph and endolymph

In 2019, Kim and Pham [95] proposed that density differences between the perilymph and endolymph might contribute to the light cupula phenomenon. They suggested that when the density of perilymph exceeds that of the endolymph, endolymphatic space within the semicircular canal experiences buoyancy from the surrounding perilymph under gravity. This buoyancy deforms the thin, flexible endolymphatic membrane, displaces endolymph, and deflects the cupula, leading to the characteristic persistent geotropic DCPN [95,96].

This hypothesis is based on the likelihood that changes in perilymph density precede those in the endolymph, as the perilymphatic space is more directly influenced by inner ear capillaries through the blood-labyrinth barrier. In contrast, the endolymphatic space is strictly isolated from the perilymphatic space by the endolymphatic membrane, which is reinforced by tight junctions. Two mechanisms have been proposed to explain the increase in perilymph density: the osmotic hypothesis, where increased plasma osmolality—such as in cases of water deficit, hormone imbalance, diabetes mellitus, uremia, and neurologic catastrophes—drives water from perilymph to blood, and the plasma protein leakage hypothesis, where blood-labyrinth barrier dysfunction allows proteins like serum albumin to enter the perilymph, raising its density.

Summary of proposed mechanisms and their explanatory scope

In brief, the first three theories attribute persistent geotropic DCPN to a relatively lighter cupula compared to the surrounding endolymph, while the latter two propose alternative mechanisms unrelated to cupula density. None of the current explanations fully explains all clinical features (Table 2). Thus, the concept of a “light cupula” represents only one potential explanation for persistent geotropic DCPN, and its use as a specific diagnostic label remains controversial. While “persistent geotropic DCPN” is an observational term, “light cupula” refers to a specific pathophysiological hypothesis, and the two do not fully overlap in meaning. Furthermore, these mechanisms may not be mutually exclusive, with elements of each potentially contributing to persistent geotropic DCPN.

Table 2 [9,12,15,16,20,25,33,37-39,42,43,55,60,62,66,71,82-85,90,94-102] summarizes these peripheral mechanisms and evaluates their explanatory scope across several clinical features. The evaluations reflect the authors’ perspectives based on the discussion in the currently available literature and may be interpreted differently by other researchers. For instance, we find a lack of case reports or studies adequately supporting the utricular dysfunction theory. Although some literature reports significant differences in SVV values in light cupula cases compared to other BPPV subtypes, this does not constitute direct evidence that utricular dysfunction alone causes the observed nystagmus. Future developments, such as new explanations or supporting studies within existing theoretical frameworks, may lead to revisions of these assessments; additional research is needed to clarify these mechanisms and explore alternative explanations yet to be discovered.

Persistent Geotropic Direction-Changing Positional Nystagmus Observed in Comorbid Conditions and Central Lesions

Vestibular migraine

Many patients with vestibular migraine experience positional vertigo, with persistent geotropic DCPN being a frequently observed pattern. In 2004, von Brevern et al. [103] described cases of vestibular migraine presenting with persistent geotropic DCPN, persistent apogeotropic DCPN, and transient pure torsional nystagmus during acute episodes. In 2010, Polensek and Tusa [104] examined 26 patients during acute vestibular migraine and found that positional nystagmus could be provoked in all symptomatic cases when visual fixation was blocked. The nystagmus was typically sustained, of low velocity (2°–7°/sec), and showed no latency, with horizontal directionality being the most common. These findings suggest that central positional nystagmus, often presenting as persistent DCPN, is a frequent and characteristic feature of vestibular migraine attacks. In 2014, Lechner et al. [105] reported persistent geotropic DCPN in five of 13 patients with acute vestibular migraine, showing symmetric and low-velocity responses during the supine head roll test, in contrast to the crescendo-decrescendo pattern of HC canalolithiasis.

In 2014, Tomanovic and Bergenius [25] found that 40% (eight of 20) of patients with sudden vestibular dysfunction and persistent geotropic DCPN had a history of migraine and met the diagnostic criteria for vestibular migraine, with 65% of these patients being women. More recently, Chang et al. [72] analyzed 56 patients with persistent geotropic or apogeotropic nystagmus and found that over half met the diagnostic criteria for vestibular migraine (30.4%, 17 of 56) or probable vestibular migraine (26.8%, 15 of 56) in 2025. Notably, more than 65% of these patients (21 of 32) exhibited typical light or heavy cupula patterns, supporting a migraine-related mechanism for positional nystagmus.

Proposed mechanisms for positional nystagmus in vestibular migraine include both central and peripheral pathways. Central pathways include dysfunction of inhibitory GABAergic connections from the vestibulocerebellum to the vestibular nuclei [103], and peripheral pathways include labyrinthine alterations due to vasospasm or neurogenic vasodilation with plasma extravasation [104]. Trigeminovascular activation may also contribute to migraine-related inner ear dysfunction by inducing fluid extravasation [72,106]. Additionally, modulation of vestibular afferents by neurotransmitters released during migraine attacks, as well as transient ischemia of the inner ear or brainstem due to vasospasm, have been proposed [107]. Ion channel dysfunction, as seen in other paroxysmal neurologic disorders, may also play a role in vestibular migraine by affecting both inner ear structures and central vestibular pathways [107]. Some of these mechanisms may alter the specific gravity of the endolymph or cupula, leading to light or heavy cupula phenomena. Growing evidence supports the pathophysiological association between migraine and positional vertigo, including associated nystagmus [42], but the precise interplay between central and peripheral processes remains unclear. Further exploration is required to deepen our understanding.

Central lesions

Persistent geotropic DCPN can occur in central lesions, complicating differential diagnosis. In 2014, Lee et al. [108] reported two cases initially misdiagnosed as HC canalolithiasis but later identified as cerebellar glioma and lateral medullary infarct. That same year, Yang and Oh [109] also described a case associated with human immunodeficiency virus encephalopathy, presenting with asymmetrical nystagmus but without spontaneous or bow and lean test nystagmus. They suggested that central persistent geotropic DCPN could result from human immunodeficiency virus (HIV)-related damage to the otolith organs, vestibular nuclei, or cerebellum, affecting graviceptive input and otolith organ-related ocular reflexes. Direct viral effects, opportunistic infections, and myelinic degeneration in the central vestibular system were proposed as contributing factors, with geotropic paroxysmal positional nystagmus potentially serving as an early manifestation of HIV-related central vestibular dysfunction.

The cerebellar nodulus and uvula, known as integrators of otolith signals, have been speculated to produce inappropriate feedback signals when disrupted, falsely indicating head rotation in the absence of movement [110]. This could explain sustained, latency-free horizontal nystagmus during the supine head roll test. Lesions in the cerebellar floculus, in particular, have been suggested as a potential cause of persistent geotropic horizontal DCPN [111]. In 2015, Kim et al. [14] suggested that, because head rolling during bowing and leaning stimulates the otolith organs in contradictory ways, it is unlikely for null points to be identified on the same side during both maneuvers in patients with cerebellar lesions.

In 2018, Choi et al. [112] found that 12% of patients with persistent geotropic DCPN had central lesions, identifying the cerebellar tonsil as the most likely site responsible. They also noted that null points could appear in central cases, though not always on the lesion side. Separately, Imai et al. [77] observed in 2015 that the time constant of SPV in persistent geotropic DCPN closely resembles that of persistent apogeotropic DCPN, the latter thought to result from a heavy cupula. They proposed that persistent geotropic DCPN may conversely arise from a light cupula of peripheral origin.

Given the anatomical axis of the HC cupula, null points are considered a key feature of HC cupulopathy [14]. In 2018, Choi et al. [112] further observed that stronger and more asymmetric nystagmus in persistent geotropic DCPN is more indicative of a peripheral origin. Overall, although central lesions can underlie some cases of persistent geotropic DCPN, such occurrences appear to be rare. Therefore, when null points align with the lesion side and neurological findings are absent, peripheral cupulopathy is a reasonable diagnosis for persistent geotropic DCPN [1,11,14,63,85].

Other comorbid conditions

In 1957, Aschan and Stahle [113] reported persistent geotropic DCPN in three of 21 Ménière disease patients during acute vertigo, speculating that the mechanism might be similar to PAN. A more recent case (2018) of a woman with congenital nystagmus and Ménière disease showed persistent DCPN with alternating “light” and “heavy cupula” patterns and two null points, providing partial support for the hypothesis that changes in endolymph density may contribute to persistent DCPN in Ménière disease [114]. In addition, a 2021 report by Noh et al. [115] described two patients who exhibited very weak but persistent geotropic or apogeotropic DCPN within hours after a Ménière attack, suggesting a transient alteration in chemical composition or electrolyte balance in the inner ear fluid as a possible mechanism. The absence of headache in both cases argues against coexisting vestibular migraine.

Persistent geotropic DCPN has also been documented in patients with SSNHL [20,32,61,63,79,90], acute otitis media with serous labyrinthitis [96,116,117], and Ramsay Hunt syndrome [118]. Meanwhile, in cases of SSNHL with vertigo, high signal intensity on three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging in the cochlea and vestibule has been reported, potentially associated with elevated endolymphatic protein levels, minor hemorrhage, or cellular disruption within the inner ear [101,119]. These findings support the hypothesis that the persistent geotropic DCPN occasionally observed in such patients may result from changes in endolymph composition.

In 2017, Choi et al. [71] reported a case of light cupula associated with meningitis, suggesting that elevated cerebrospinal fluid protein may have increased endolymph density. Although meningitis itself does not directly involve the brain parenchyma or brainstem, its complications can mimic central lesions. However, the absence of neurological signs and unremarkable brain imaging led the authors to diagnose the condition as light cupula, a peripheral vestibular phenomenon.

In 2018, Choi et al. [120] reported a case of persistent geotropic DCPN after middle ear surgery, suggesting that the condition resulted from alterations in inner ear fluids caused by the penetration of toxic substances, such as antibiotics or blood, into the inner ear or by disruption of the inner ear membrane during stapes mobilization.

In patients with light cupula accompanied by ipsilateral inner ear disorders, identifying null points may be challenging, and transitions from geotropic to apogeotropic nystagmus appear to occur more frequently compared to typical cases of light cupula [53,116]. Several studies have documented transitions between persistent geotropic and apogeotropic DCPN, offering insights into the mechanism of light cupula. In 2015, Shin et al. [53] reported a case of SSNHL with persistent geotropic DCPN that transitioned to persistent apogeotropic DCPN. They suggested that an initial light cupula, caused by increased endolymphatic density, transformed into a heavy cupula due to the attachment of otoconial debris. Similarly, in transitions from apogeotropic to geotropic DCPN, swollen otoconial debris may reduce its density, reversing the nystagmus direction. Alternatively, this phenomenon might result from the overcompensation of endolymphatic homeostasis [53].

Treatments

Although no definitive treatments for persistent geotropic DCPN have been established, various methods have been attempted, offering potential insights into the underlying mechanisms of light cupula. Studies on traditional maneuvers have reported extremely low success rates [29,57,63,64]. For instance, the barbecue roll maneuver, commonly used for transient geotropic DCPN, has shown no effectiveness (0% success rate) for persistent geotropic DCPN [64]. Its efficacy remained low whether the lesion side was determined by the null plane or by the side with stronger nystagmus [31]. In contrast, the Gufoni maneuver achieved a 60% immediate success rate in apogeotropic DCPN cases, likely involving HC cupulolithiasis and anterior arm canalolithiasis, both assuming otoconial debris as the underlying cause [2]. This stark disparity in success rates highlights fundamental differences in their underlying mechanisms.

In 2018, Kim and Hong [66] introduced a modified repositioning maneuver for light cupula, involving mastoid oscillation to dislodge light debris from the cupula and redirect it against gravity into the utricle. Despite this targeted approach, the maneuver was ineffective in treating persistent geotropic DCPN. These findings suggest that persistent geotropic DCPN may not be caused by light debris attached to the cupula but rather by other mechanisms, such as a lighter cupula or heavier endolymph. The lack of efficacy of repositioning maneuvers in light cupula cases underscores the need for further investigation into its distinct pathophysiology.

In 2016, Cha et al. [121] reported a case of light cupula in which positional vertigo resolved immediately after transcutaneous vagus nerve stimulation (tVNS), though the mechanism remained unclear and nystagmus later recurred. The authors hypothesized that tVNS might modulate the vestibulosympathetic pathway through a top-down mechanism, helping to normalize HC hyperexcitability and correct autonomic imbalance.

Intratympanic steroid injections are commonly used to manage certain inner ear conditions, including SSNHL, tinnitus, and Ménière disease. These injections are believed to reach the perilymph, where they may help reduce inner ear inflammation, improve blood circulation, and restore balance between endolymph and perilymph densities. In 2018, Park et al. [36] explored the therapeutic potential of these injections to alleviate dizziness in light cupula patients. Although they observed some symptom improvement and a reversal of nystagmus in certain cases, the overall effect was not statistically significant.

While positional nystagmus in light cupula typically resolves spontaneously within 2 weeks, cases accompanied by SSNHL may exhibit nystagmus persisting for several months or longer [79,90]. Intractable cases may require surgical intervention, such as semicircular canal plugging, to treat persistent positional nystagmus [79]. Considering that light cupula often has a prolonged course and may coexist with other inner ear conditions, early diagnosis is crucial to avoid unnecessary repositioning maneuvers. In patients with a history of Ménière disease, vestibular migraine, SSNHL, or central nervous system disorders, light cupula should be considered as part of the clinical presentation. In such cases, both symptom relief and targeted treatment of the comorbid condition are essential. Given the potential association between light cupula and vestibular migraine, treatment strategies for vestibular migraine—such as lifestyle modifications and prophylactic medications—may help promote symptom resolution or reduce recurrence in selected patients [72].

CONCLUSIONS

This review recognizes persistent geotropic DCPN as a clinical phenomenon that can arise from both peripheral and central origins. The concept of “light cupula” has emerged as a key hypothesis to explain many cases of peripheral origin. However, alternative mechanisms have also been proposed. None of these hypotheses fully account for all observed clinical features, suggesting that persistent geotropic DCPN may arise from case-specific distinct mechanisms or yet undiscovered explanations.

Distinguishing peripheral persistent geotropic DCPN from central causes remains a critical challenge. Accurate differentiation requires careful observation of key features, such as nystagmus patterns, null points, and the identification of central signs. This differentiation is essential to avoid misdiagnosis and guide appropriate treatment strategies.

Persistent geotropic DCPN associated with other otologic comorbidities or central lesions often relies on case reports for insights. These reports provide valuable information for clinicians to minimize misclassification, reduce unnecessary repositioning maneuvers and additional tests, and offer appropriate treatment and prognostic guidance.

The lack of comprehensive guidelines addressing persistent geotropic DCPN underscores the need for further research. Future efforts should focus on elucidating the underlying mechanisms, refining diagnostic criteria, and identifying effective management strategies. Enhanced understanding of persistent geotropic DCPN will ultimately improve clinical outcomes and the quality of care for affected patients.

ARTICLE INFORMATION

Funding/Support

This work was supported by Konkuk University Medical Center Research Grant 2024.

Conflicts of Interest

No potential conflict of interest relevant to this article was reported.

Availability of Data and Materials

The datasets are not publicly available but are available from the corresponding author upon reasonable request.

Authors’ Contributions

Conceptualization, Project administration: CHK; Data curation, Formal analysis, Methodology, Visualization: DHL, CHK; Writing–original draft: DHL, CHK; Writing–review and editing: DHL, CHK.

All authors read and approved the final manuscript.

Fig. 1.

Search flowchart for article selection in this review.

Fig. 2.

Persistent geotropic direction-changing positional nystagmus in positional alcohol nystagmus (PAN-I).

Fig. 3.

Persistent geotropic direction-changing positional nystagmus and null points in right-sided light cupula patient.

Fig. 4.

Bow and lean test and three null points in right-sided light cupula patient.

Fig. 5.

Asymmetric cupula deflection during supine head roll test and its impact on nystagmus intensity.

Table 1.

Differential diagnosis of HC disorders presenting with DCPN

Variable	HC canalolithiasis (posterior arm)	HC canalolithiasis (anterior arm)	HC cupulolithiasis (heavy cupula)	Light cupula
Duration	Transient	Transient or persistent^a)	Persistent	Persistent
DCPN	Geotropic	Apogeotropic	Apogeotropic	Geotropic
Null point	–	–	+	+
Latency	+	+	–	–
Fatigability	+	+	–	–

HC, horizontal semicircular canal; DCPN, direction-changing positional nystagmus.

^a)In HC canalolithiasis of anterior arm, nystagmus may persist for more than 1 minute when the healthy ear is down.

Table 2.

Suggested peripheral mechanisms and their explanatory scope for persistent geotropic direction-changing positional nystagmus

Clinical feature	Suggested mechanism
Clinical feature	Lighter cupula	Heavy endolymph	Light debris	Utricular dysfunction	Perilymp-endolymph density difference
Horizontal semicircular canal prevalence	X [71]	X [33,39,43,60,71,97]	O [33,39,55,97]	△	X [95]
Supported by cases or studies?	O [9,12,98-100]	O [71,82-84,101,102]	X [16]	X [20,60,62,94]	△ [95,96]
Explains rapid onset and short course?	△ [37]	△ [37,39,60,85,97]	O [37,39,97]	△	△ [95]
Supports heavy-light cupula conversion?	O [16]	O [16]	O [16,90]	△	O [96]
Explains repositioning failure?	O [42,66]	O [42,66]	X [25,66,97]	O	O [96]
Explains null point and its variation?	△ [12]	△ [12,38]	O [15]	X [60]	X [38]

O, consistent or supported; X, not consistent or not supported; △, debatable or indeterminate.

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Persistent geotropic direction-changing positional nystagmus: a systematic review

Res Vestib Sci. 2025;24(3):153-176. Published online September 15, 2025

DOI: https://doi.org/10.21790/rvs.2025.002

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Persistent geotropic direction-changing positional nystagmus: a systematic review

Fig. 1. Search flowchart for article selection in this review.

Fig. 2. Persistent geotropic direction-changing positional nystagmus in positional alcohol nystagmus (PAN-I).

Fig. 3. Persistent geotropic direction-changing positional nystagmus and null points in right-sided light cupula patient.

Fig. 4. Bow and lean test and three null points in right-sided light cupula patient.

Fig. 5. Asymmetric cupula deflection during supine head roll test and its impact on nystagmus intensity.

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

Persistent geotropic direction-changing positional nystagmus: a systematic review

Variable	HC canalolithiasis (posterior arm)	HC canalolithiasis (anterior arm)	HC cupulolithiasis (heavy cupula)	Light cupula
Duration	Transient	Transient or persistent^a)	Persistent	Persistent
DCPN	Geotropic	Apogeotropic	Apogeotropic	Geotropic
Null point	–	–	+	+
Latency	+	+	–	–
Fatigability	+	+	–	–

Clinical feature	Suggested mechanism
Clinical feature	Lighter cupula	Heavy endolymph	Light debris	Utricular dysfunction	Perilymp-endolymph density difference
Horizontal semicircular canal prevalence	X [71]	X [33,39,43,60,71,97]	O [33,39,55,97]	△	X [95]
Supported by cases or studies?	O [9,12,98-100]	O [71,82-84,101,102]	X [16]	X [20,60,62,94]	△ [95,96]
Explains rapid onset and short course?	△ [37]	△ [37,39,60,85,97]	O [37,39,97]	△	△ [95]
Supports heavy-light cupula conversion?	O [16]	O [16]	O [16,90]	△	O [96]
Explains repositioning failure?	O [42,66]	O [42,66]	X [25,66,97]	O	O [96]
Explains null point and its variation?	△ [12]	△ [12,38]	O [15]	X [60]	X [38]

Table 1. Differential diagnosis of HC disorders presenting with DCPN

HC, horizontal semicircular canal; DCPN, direction-changing positional nystagmus.

In HC canalolithiasis of anterior arm, nystagmus may persist for more than 1 minute when the healthy ear is down.

Table 2. Suggested peripheral mechanisms and their explanatory scope for persistent geotropic direction-changing positional nystagmus

O, consistent or supported; X, not consistent or not supported; △, debatable or indeterminate.