Clinical Characteristics of persistent geotropic horizontal direction-changing positional nystagmus: Experience in 189 participants

1 Introduction

Benign paroxysmal positional vertigo (BPPV) that characterized as episodic vertigo and nystagmus is caused by fragments of degenerating otoconia that move freely in the semicircular canal (canalolithiasis) or are attached to the cupula (cupulolithiasis) and thereby displace the cupula, producing asymmetric vestibular stimulation that leads to vertigo and nystagmus [7]. Lateral semicircular canal BPPV (LSC-BPPV) is the most common type of BPPV second to posterior semicircular canal BPPV (PSC-BPPV).

The subtypes of LSC-BPPV depend on the direction-changing positional nystagmus (DCPN) in the supine roll test (SRT) [24]. The geotropic variant due to canalolithiasis of the posterior part of the LSC shows a transient (< 1 min)geotropic horizontal DCPN, the apogeotropic variant due to canalithiasis of the anterior part of the LSC near the cupula shows a transient apogeotropic horizontal DCPN, and the apogeotropic variant due to cupulolithiasis or heavy cupula shows persistent (> 2 min) apogeotropic horizontal DCPN. However, persistent geotropic horizontal DCPN is thought to be caused by the lower specific gravity of the LSC cupula than its surrounding endolymph, namely, the light cupula. Previous studies [9, 27] have illustrated the clinical characteristics of the persistent geotropic horizontal DCPN: intractable barbecue roll maneuver, spontaneous resolution tendency (in one week), and ease of recurrence.

The etiology and mechanism of the persistent geotropic horizontal DCPN are still unclear. Several hypotheses have been proposed. The light debris cupulolithiasis hypothesis [4, 9] states that light particles attach to the lateral semicircular cupula and cause the cupula to move upward. However, the identification of light particles has not been reported thus far. The light cupula hypothesis is derived from the positional alcohol nystagmus (PAN) described by Aschan [1]. The heavy endolymph hypothesis assumes that the density or viscosity of endolymph rises due to peripheral hypofusion, labyrinth bleeding, inflammation, or hormone imbalance [5, 15]. Kim [13] proposed the density hypothesis, wherein the density discrepancy between the peri- and endolymph might account for the light cupula. However, none of these hypotheses can perfectly explain this phenomenon. Whether the persistent geotropic horizontal DCPN is a subtype of BPPV remains controversial.

The purpose of this study is to observe and summarize the distribution and clinical characteristics of participants with the persistent geotropic horizontal DCPN to further understand this phenomenon.

2 Methods

2.7 Definition of converted DCPN

We defined converted DCPN as the conversion of patterns of DCPN in the history, in the follow-up tests and in the recurrence compared to the first showing of PGHDCPN. We counted the converted DCPN involving different semicircular canals and the different affected sides.

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Fig. 1

Manifestations in follow-up tests.

In this study, the distribution data of the PGHDCPN were similar to those of BPPV reported previously. The mean age of the onset of PGHDCPN participants was 56 years, which was slightly older than previous studies reporting a mean age of 49.3 to 52.8 [22, 25] for BPPV. More than half of the PGHDCPN participants (52.3%) were older than 60, consistent with the age characteristics of BPPV. It was previously reported that BPPV had a peak age of onset in the sixth decade for idiopathic BPPV [3]. More women than men are affected by PGHDCPN (female-to-male ratio 2.4 : 1). The ratio is slightly higher than BPPV, reported as 1.5–2.2 : 1 [16]. The basis of the female preponderance in BPPV is not known but may be related to osteoporosis, migraine, or both [23]. The higher female ratio in PGHDCPN than BPPV indicated that osteoporosis might play a more important role in the PGHDCPN. Ichijo et al. [12] reported that BPPV predominantly affects the right labyrinth in both sexes. This preponderance is due to the laterality of the sleeping position. However, our study found that the side preponderance of the PGHDCPN was not as prominent as BPPV, which might be attributed to the fact that sleeping position is not always the same each night, and ordinary people turn over in bed many times per night.

Of the participants who came for the first-week follow-up test,60.6% were asymptomatic and showed non-observable nystagmus in positional test. Previous studies reported that the remission rates of PGHDCPN (light cupula) in the first-week follow-up were 42.9% [3] and 70.4% [22]. The etiology of spontaneous remission of PGHDCPN is due to the dissolve of the light debris or the compensation of the specific gravity of the endolymph. However, the remission rates at 1 week are variable maybe due to the different time of the symptoms prior to being treated.

Data on the recurrence rate of PGHDCPN are scarce. Seo [19] reported 33% based on 27 light cupula (PGHDCPN) cases, and Ichijo [11] reported 72.3% based on 34 light cupula cases. However, in our study, the recurrence rate of PGHDCPN was only 17.1%, which war much lower. Although we asked participants to revisit if they experienced a recurrence of vertigo, not all of them came. The reasons are multiple: some participants will not come back for the vertigo when they knew that the disease was not a big problem, or they might go to other hospital. Meanwhile, the observation time was not long enough. Therefore, we might have underestimated the recurrence rate. Previous studies reported that all types of BPPV and LSC-BPPV recurrence were 7% –56% [18] and 20% –38.5% [19], respectively. When compared to BPPV, we found that the recurrence of the PGHDCPN was lower but much closer to that of LSC-BPPV. Previous studies reported that sex did not impact BPPV recurrence [14, 22]. However, we found that more women than men experienced recurrence, and the sex ratio of PGHDCPN recurrence was nearly two times higher than the sex ratio of prevalence (4.5 : 1 vs. 2.4 : 1). Except for the osteoporosis and the migraine states above, the reason for the female preponderance in recurrence may also due to the higher rate of revisit for the women.

The patterns of DCPN in the history, in follow-up tests and in the recurrence were not always the same as the first showing PGHDCPN. Conversion of the patterns of DCPN had been reported previously. Ichijo [11] reported that 9/33 light cupula changed to cupulolithiasis or heavy cupula in recurrence. Shin [21] reported the conversion between persistent geotropic and apogeotropic DCPN in patients with sudden hearing loss and cupulopathy. He concluded that these two groups’ clinical characteristics during conversion were different. In our study, conversion of patterns of DCPN were observed in 28.0% of PGHDCPN participants. The mechanism of the conversion phenomenon is unclear. We speculated the followings to be the potential causes behind this phenomenon. 1.The otolith particles that attached to the cupula or in the LSCC subsequently change into light debris because of degeneration or decalcification. This might explain the conversion of TGHDCPN to PGHDCPN. 2 the light debris in the LSCC experienced increase of density due to concentration or gathering. This might explain the conversion of PGHDCPN to TGHDCPN or the conversion of PGHDCPN to PAHDCPN. So, we assumed that these two types of PGHDCPN with converted tendency might be a subtype of BPPV or in a stage of BPPV process. 3 a change in the specific gravity of the endolymph due to over-compensation. This might explain the conversion between PGHDCPN and PAHDCPN. As for the conversion between PGHDCPN and TTVDCPN (posterior/ anterior canalolithiasis) might not be the same diseases because the affected canals are different. We should observe for longer time to figure out this phenomenon. Furthermore, 24(12.1%) PGHDCPN participants still experienced PGHDCPN attack in the follow-up tests and the recurrences without BPPV history. We speculate this non-converted type of PGHDCPN might be an independent disease that is not related to BPPV. However, longer periods should be observed to ensure that the PGHDCPN patterns will not change. Meanwhile, we speculated that if the time interval between the DCPNs is relatively long and each DCPN occurs abruptly rather than gradually, the conversion phenomenon might also be explained by simple independent attack even if the affected side and semicircular canal is same.

The affected sides differed in the converted PGHDCPN participants. Of the 53 converted PGHDCPN participants, 28.3% (15/53) differed in the affected sides, In a strict sense, the different affected sides relapse may not be the same disease. However, it happens sometimes. The phenomenon was also seen in BPPV. Perez et al. [18] reported that 37% of BPPV recurrences affected the contralateral ear. Shigeno [20] showed that 17% of BPPV recurrences were on the opposite side. These phenomena indicate that these converted PGHDCPN participants have some constitution that produces pathological debris similar to the BPPV participants.

5 Limitations

Some limitations of our work should be underlined. First, this study was started from 2014. Due to the limited previous understanding of light cupula, we did not collect complete clinical information, such as detailed vertigo histories; take other vestibular function tests; or observe the episode duration or relationship of PGHDCPN to migraine, sudden sensorineural hearing loss (SSHL) and central vertigo. Second, many participants were lost to follow up. As a result, the recurrence rate was probably heavily underestimated.

6 Conclusion

PGHDCPN affected more women than men. PGHDCPN that manifested conversion to TGHDCPN or to PAHDCPN might be a subtype of BPPV or in a stage of BPPV process. However, the PGHDCPN without conversion might be an independent disease that is not related to BPPV.