RE: BENIGN PAROXYSMAL POSITIONAL VERTIGO: CANAL SWITCHING AFFECTING ALL CANALS DURING A SINGLE SESSION.

Abstract

To the Editor We read and watched with interest the video report “Benign paroxysmal positional vertigo (BPPV): canal switching (CS) affecting all canals during a single session” (1). The authors believed that they encountered a rare case of BPPV affecting sequentially all three canals in the right side including posterior canal (PC), superior canal (SC), and lateral canal (LC) due to CS during a single session. However, we have several concerns for this report. First, as shown in the video, the patient firstly underwent a right Dix-Hallpike maneuver (DHM) that showed a positional upward and torsional-beating nystagmus (pUBN) indicating a typical right PC canalithiasis (2), subsequently received a canalith repositioning maneuver (CRM) for PC-BPPV(3), and then obtained a repeat DHM to evaluate CRM efficacy, showing a positional downward and torsional-beating nystagmus(pDBN). Authors thought that the pDBN was consistent with the right SC canal-ithiasis, which was due to CS from PC to SC during the CRM. We think that the right SC canalithiasis due to CS should be insufficient to be identified, as more likely present of apogeotropic PC-BPPV (aPC-BPPV) (4–6). In term of spatial orientation of the semicircular canals, the right PC is in the same plane as contralateral (left) SC. According to Ewald’ first law that the eye movements evoked by stimulation of a individual canal align with the plane of that canal (7), in the right DHM, the right PC or the left SC rather than the right SC should be responsible for the induced pDBN. Moreover, if this pDBN might be induced by the right SC canalithiasis due to CS, it should be more likely provoked by contralateral (left) rather than ipsilateral (right) DHM, but contralat-eral DHM was not indicated in the report. In BPPV, pDBN with or without a torsional component is traditionally linked to AC-BPPV (8), however pDBN is not always because of SC-BPPV and also generated from aPC-BPPV variant (4–6). Differentiating aPC-BPPV from contralateral SC canalithiasis is challenging as both presenting with similar pDBN in the DHM on same side (4,9), although video head impulse test may be used for detecting the affected canal (9). In the patient, pre-existing contralateral (left) SC-BPPV was not indicated on the initial right DHM. Therefore, the pDBN on the second DHM should originate from ipsilateral (right) aPC-BPPV (6,10). aPC-BPPV as a rare variant of PC canalithiasis distinguishing from typical PC canalithiasis has been reported extensively, for which it is hypothesized that otoconia settling in the nonampullary arm of PC may result in pDBN (4–6,9–11). After CRM, a typical PC canalithiasis can change into aPC-BPPV (10). It was indicated that in the reported case, the aPC-BPPV was resulted from a transformation from the canalothiasis of ampullary arm of right PC (a typical PC canalothiasis with pUBN) to the canal-othiasis of nonampullary arm of same canal (an a typical PC canalothiasis with pDBN) during the CRM or consequent DHM (10,12). The transformation, or an ipsilateral PC switch, should be due to remaining of otoconia in the nonampullary arm of PC after CRM (10) or re-entering of otoconia, which were moved out from PC into the utricle by CRM, into the nonampullary arm of PC from the utricle during subsequent DHM (12–14). Second, the patient was diagnosed as having SC-BPPV due to CS during the first CRM based on the pDBN in following DHM, and immediately she was treated again with a CRM. Afterthen, diagnostic test suggested that the right LC canalithiasis occurred as presenting with a horizontal geotropic nystagmus (2,3). Authors believed that the LC canalolithiasis was also due to CS, a conversion from SC canalolithiasis. We think it indeed was CS, but it should be a conversion to LC canalolithiasis from aPC-BPPV rather than SC-BPPV. Third, as shown in the video, short interval time was set aside between repositioning and diagnostic maneuvers, which should be associated with the occurrence of CS or reentry in the reported case. Although repeated repositioning and diagnostic maneuvers within the same session is considered as a safe and effective approach to the management of BPPV, with a low risk of CS (15,16), enough interval between maneuvers should set aside to avoid the occurrence of CS or re-entry conditions (12–14). There is not yet a consensus on interval time between maneuvers (15), a study suggested that at least a 15-minitus interval time between maneuvers should be kept out, which may decrease the incidence of CS or re-entry (14). Xizheng Shan, M.D.Entong Wang, M.D., Ph.D. Department of Otolaryngology – Head and Neck Surgery, Beijing Electric Power Hospital, Beijing, China [email protected]