10.14639/0392-100X-N2016
Objective. To study the frequency of canal switch in posterior canal benign paroxysmal positional vertigo (BPPV) treated by canalith repositioning manoeuver (CRP), quick liberatory rotation manoeuver (QLR) or Semont manoeuver (SM). Methods. Retrospective study on 1158 patients, 637 women and 521 men suffering from geotropic posterior canal BPPV treated by CRP, QLR, or SM, retested after 15 minutes and about seven days. Results. 1146 patients recovered from the acute phase; treatments failed in 12 patients treated with CRP. We observed 12 canal switches from posterior to lateral canal and 2 from posterior to anterior canal during or after CRP in 13/879 cases (1.5%) and after QLR in 1/158 (0.6%) with no significant difference between CRP vs SM and QLR. We did not consider slight positional downbeat nystagmus after the therapeutic manoeuvers as a sign of canal switch into the anterior canal, but as a sign of persistent small debris in the nonampullar arm of the posterior canal. Conclusions. Canal switch is rare for any manoeuver and it does not belong to the criteria to choose one manoeuver over another. Notably, due to the canal switching criteria, SM and QLR cannot be preferred over those with a more prolonged extension of the neck.
text/xml
1827-675X
2016
en
Luigi Califano
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
liberatory manoeuver
Canal switch: a possible complication of physical therapeutic manoeuvers for posterior canal benign paroxysmal positional vertigo
Text.Serial.Journal
https://www.actaitalica.it/
43
Vestibology
2023-02-27
2022-01-21
2023-02-28
2023-02-28
49-55
1
Luigi Califano
2023/02/27
10.14639/0392-100X-N2016
49
San Pio Hospital, Department of Audiology and Phoniatrics, Benevento, Italy
1827-675X
liberatory manoeuver
en
55
Canal switch: a possible complication of physical therapeutic manoeuvers for posterior canal benign paroxysmal positional vertigo
https://www.actaitalica.it/article/download/2016/918
43
ACTA OTORHINOLARYNGOLOGICA ITALICA 2023;43:49-55; doi: 10.14639/0392-100X-N2016




Vestibology


Canal switch: a possible complication of physical
therapeutic manoeuvers for posterior canal benign
paroxysmal positional vertigo
Lo switch canalare: possibile complicanza della terapia liberatoria per la VPPB
del canale posteriore
Leonardo Scotto di Santillo1, Luigi Califano2
1
 ASL 3 Genovese, S.S. Vestibology and Vestibular Rehabilitation, Genoa, Italy; 2 San Pio Hospital, Department of Audiology and
Phoniatrics, Benevento, Italy


SUMMARY
Objective. To study the frequency of canal switch in posterior canal benign paroxysmal
positional vertigo (BPPV) treated by canalith repositioning manoeuver (CRP), quick libera-
tory rotation manoeuver (QLR) or Semont manoeuver (SM).
Methods. Retrospective study on 1158 patients, 637 women and 521 men suffering from
geotropic posterior canal BPPV treated by CRP, QLR, or SM, retested after 15 minutes and
about seven days.
Results. 1146 patients recovered from the acute phase; treatments failed in 12 patients
treated with CRP. We observed 12 canal switches from posterior to lateral canal and 2
from posterior to anterior canal during or after CRP in 13/879 cases (1.5%) and after QLR
in 1/158 (0.6%) with no significant difference between CRP vs SM and QLR. We did not
consider slight positional downbeat nystagmus after the therapeutic manoeuvers as a sign
of canal switch into the anterior canal, but as a sign of persistent small debris in the non-
ampullar arm of the posterior canal.
Conclusions. Canal switch is rare for any manoeuver and it does not belong to the criteria
to choose one manoeuver over another. Notably, due to the canal switching criteria, SM and
QLR cannot be preferred over those with a more prolonged extension of the neck.                  Received: February 6, 2022
                                                                                                 Accepted: November 15, 2022
KEY WORDS: posterior canal BPPV, canalolithiasis, repositioning manoeuver, liberatory
manoeuver                                                                                        Correspondence
                                                                                                 Leonardo Scotto di Santillo
RIASSUNTO                                                                                        ASL 3 Genovese, S.S. Vestibology and Vestibu-
                                                                                                 lar Rehabilitation, via L.A. Vassallo 3/24, 16146
Obiettivo. Studiare la frequenza del fenomeno dello switch canalare come complicanza
                                                                                                 Genoa, Italy
delle manovre terapeutiche in fase acuta della BPPV da canalolitiasi posteriore geotropa.        E-mail: lescott@tin.it
Metodi. Studio retrospettivo includente 1158 pazienti, 637 donne e 521 uomini affetti da
BPPV da canalolitiasi posteriore in fase acuta trattati in sedi diverse con manovra di ripo-
sizionamento (CRP) (879 pazienti), Manovra di Rotazione Rapida Liberatoria (QLR) (158              How to cite this article: Scotto di Santillo L,
pazienti) o manovra di Semont (SM) (121 pazienti). Il retest è stato effettuato 15 minuti e        Califano L. Canal switch: a possible complica-
circa 7 giorni dopo l’esecuzione della manovra terapeutica.                                        tion of physical therapeutic manoeuvers for pos-
                                                                                                   terior canal benign paroxysmal positional ver-
Risultati. 1146 pazienti sono guariti dalla fase acuta, 12 pazienti hanno presentato per-
                                                                                                   tigo. Acta Otorhinolaryngol Ital 2023;43:49-55.
sistenza dei segni e sintomi dopo l’intera procedura terapeutica. Il canal switch è stato          https://doi.org/10.14639/0392-100X-N2016
osservato in 12 casi dal canale posteriore al canale laterale, in 2 casi dal canale posteriore
al canale anteriore, durante o dopo CRP in 13/879 casi (1,5%), dopo QLR in 1/1508 casi           © Società Italiana di Otorinolaringoiatria
(0,6%).                                                                                          e Chirurgia Cervico-Facciale
Conclusioni. Il rischio di switch canalare appare molto basso per tutte le manovre uti-
lizzate, tanto da non poter essere incluso tra i criteri di scelta di una manovra rispetto ad                   OPEN ACCESS
un’altra. In particolare, il basso rischio non fa preferire la SM o la QLR rispetto a quelle
                                                                                                 This is an open access article distributed in accordance with
con maggiore e più prolungata estensione del collo.                                              the CC-BY-NC-ND (Creative Commons Attribution-Non-
                                                                                                 Commercial-NoDerivatives 4.0 International) license. The
PAROLE CHIAVE: VPPB, canalolitiasi posteriore, manovre di riposizionamento, manovre
                                                                                                 article can be used by giving appropriate credit and mentio-
liberatorie                                                                                      ning the license, but only for non-commercial purposes and
                                                                                                 only in the original version. For further information: https://
                                                                                                 creativecommons.org/licenses/by-nc-nd/4.0/deed.en




                                                                                                                                                           49
L. Scotto di Santillo, L. Califano




Introduction                                                     In all manoeuvers, “liberating nystagmus”, either in the
                                                                 nose-down position or seated, is regarded as a favourable
Benign paroxysmal positional vertigo (BPPV) 1 is the             prognostic index 2,6,8.
most frequent balance disorder in all neuro-otological           A canal switch occurs when otoliths, during or after the
series. During the acute phase, its typical symptoms are         therapeutic manoeuver, instead of moving into the utricle,
brief episodes of recurrent vertigo occurring when the           migrate into another semicircular canal, or if they re-enter
head changes position in the critical plane.                     from the utricle into a canal other than the one affected
BPPV is thought to be due to either canalithiasis (free-float-   previously.
ing otoconia in the semicircular canals) or cupulolithiasis      Posterior canal-anterior canal, posterior canal-lateral ca-
(otoconia adherent to the ampullar cupula). Posterior canal      nal, and lateral canal-posterior canal switches have been
BPPV is most common (about 75-85%) and lateral canal             described 9-11, as well as the switch from the geotropic
BPPV is less frequent (about 20%); anterior canal BPPV           form of the posterior canal BPPV to the apogeotropic
is much less frequent (1-2%) because of the highest ana-         form of the same canal 12.
tomic position of the canal. The disease can recover spon-       Two experienced operators carried out this retrospective
taneously within a few days/weeks, otherwise the patient         study using similar operative procedures in two differ-
must be treated by a physical manoeuver. Drugs, except           ent hospitals, intending to assess the incidence of canal
for antiemetics when needed, are not considered relevant         switch in a large series of geotropic posterior canal BPPV
in clinical management. During any therapeutic procedure,        treated with CRP, QLR, or SM.
head movements and the affected canal must be coplanar
to each other for an optimal effect. The Canalith Reposi-
tioning Procedure (CRP) 2 is a safe and effective treatment      Patients and methods
for patients with posterior canal BPPV. With some minor          1158 patients, 637 women (55.1%) and 521 men (44.9%),
changes over the years 3, it is a four-step process. The pa-     suffering from geotropic posterior canal BPPV were en-
tient is quickly pushed back from the sitting position to        rolled in the study from January 2019 to December 2020,
the Dix-Hallpike (DH) position on the affected side; the         either at the S.S. Vestibology and Vestibular Rehabilita-
patient’s head is turned to the contralateral DH position        tion ASL 3 Genovese or the SSD of Audiology and Pho-
slowly and continuously, and then rotated with the nose          niatrics of the A.O.R.N. San Pio, Benevento, both in Italy.
45° downward. About two minutes afterward, the patient           Using infrared video goggles, in the sitting position we
returns seated, with the head slightly bent forward. During      searched for spontaneous nystagmus, gaze-evoked nys-
the manoeuver, otoconia are “guided” back to the utricle,        tagmus and Bowing-leaning nystagmus; in the supine po-
leaving the affected canal. Mastoid vibration, performed in      sition, we searched for positioning nystagmus from lateral
the original Epley’s manoeuver, is currently used only in        canal BPPV through the Pagnini-McClure supine head
some therapy-resistant cases. Infrared video goggles allow       roll test, and positioning nystagmus from posterior canal
observing nystagmus during the entire manoeuver and not          BPPV through the Dix-Hallpike test (DH-T). Diagnosis
just in its final positions (nose-down and sitting). Nystag-     of posterior canal BPPV rested on recognition of its typi-
mus maintaining the same direction during all the steps          cal paroxysmal upbeat and torsional geotropic nystagmus,
of the manoeuver is considered a good prognostic indica-         with a latency of up to 30 seconds – usually less than 10
tor (“liberating” or “loading” nystagmus); on the contrary,      seconds – and lasting less than one minute, according to
reversed nystagmus indicates an ampullopetal movement            the Diagnostic Criteria of the Barany Society 1.
of the otoconia, which means failure of the procedure. For       Immediately after diagnosis, we carried out a therapeutic
its favourable properties, CRP is widely applied in daily        manoeuver. In the case of neck problems, such as osteopo-
clinical practice 5. The quick liberatory rotation manoeu-       rosis, hernia, stiffness, or recent trauma, we preferred SM
ver (QLR), described by Califano in 2003 6, is a variant of      that least engages the neck in its execution; otherwise, we
CRP. It differs from CRP because the patient is translated       performed either CRP without premedication and mastoid
from the side of the positive DH to the contralateral 45°        vibration or QLR. During treatment, we searched for the
nose-down position in about one second.                          appearance of the “liberating” nystagmus as a sign of the
In the Semont manoeuver (SM) 7 the patient rapidly               ampullofugal shift of otoconia, congruous with the excita-
moves in the frontal plane, starting from the diagnostic         tion of the affected posterior semicircular canal. It has a
position (45° nose-up on the affected side) and reaching         favourable prognostic relevance. We re-tested all patients
the contralateral side with the nose 45°down in about one        after 15 minutes and about seven days after the manoeu-
second. After 2-3 minutes, the patient sits back-up.             ver. Negative DH-T and Supine head roll test were consid-



50
                                                                                                                       Canal switch from posterior canal BPPV




ered the recovery indicators of the acute phase. After three
unsuccessful manoeuvers, we used a different procedure:
SM if we previously used either CRP or QLR; CRP or
QLR if we had used SM. If two more manoeuvers did not
solve the acute phase, the patient performed the Brandt-
Daroff home protocol, a brain MRI was scheduled, and
treatment was classified as “failure”.
Because head hyperextension is maintained for a longer
time in CRP, whereas it is limited to the diagnostic phase
both in SM and QLR, we compared the frequency of the
canal switch in two groups: CRP vs QLR and SM.
Statistical analysis was performed with Graph Pad Soft-
ware using Fisher’s exact test to evaluate differences in
determining canal switch between CRP vs. QLR and SM.                                Figure 2. Timing of posterior-lateral canal switches.

Results
                                                                                    cases we detected nystagmus from ipsilateral lateral canal
Mean age of the study cohort was 59.3 years ± 12.76                                 BPPV at DH retest; in 4 patients we observed the switch
(range 19-96 years), without a significant difference be-                           at the follow-up visit after about seven days (Fig. 2).
tween genders. The right side was involved in 624 cases
                                                                                    Three patients underwent 3 manoeuvers; nine patients
(53.9%), and the left in 522 (45.1%); bilateral posterior
                                                                                    had been treated with either a single CRP (8 cases) or
canal BPPV was observed in 12 cases (1%). We treated
                                                                                    a single QLR (one case). Paroxysmal horizontal nystag-
879 patients primarily with CRP, 158 with QLR, and 121
                                                                                    mus evoked during DH-T prompted us to verify by the
with SM (Fig. 1), performing 1.7 ± 0.86 therapeutic ma-
                                                                                    Pagnini-McClure supine head roll test the involvement
noeuvers per canal (range 1-5). 1146 patients recovered
                                                                                    of the ipsilateral lateral canal. In 10 patients we found
from the acute phase; treatments failed in 12 patients
                                                                                    geotropic horizontal nystagmus of greater intensity on
primarily treated with CRP. Posterior canal-lateral canal
switches, characterised by paroxysmal nystagmus from                                the side previously affected by posterior canal BPPV; we
lateral canal BPPV, were observed in 12 patients (1.03%),                           treated these patients with Gufoni manoeuver. In 2 pa-
11 treated with CRP and one with QLR. In 3 patients the                             tients we observed the shift posterior canal-apogeotropic
switch occurred during the CRP while passing from the                               lateral canal, with horizontal apogeotropic nystagmus of
central position to the contralateral DH position; in 5                             similar intensity on both sides. Head-shaking in the su-
                                                                                    pine position converted them in the geotropic form, which
                                                                                    was successfully treated with the Gufoni manoeuver. At
                                                                                    the immediate retest, we observed two posterior canal-
                                                                                    anterior canal switches in patients treated with CRP, and
                                                                                    mild downbeat and torsional nystagmus compatible with
                                                                                    the apogeotropic variant of the affected posterior canal
                                                                                    BPPV in 53/1158 patients (4.6%). In this circumstance,
                                                                                    we avoided the immediate treatment, performing it at the
                                                                                    7-day follow-up visit if nystagmus persisted (8/53 cases,
                                                                                    15.1%).
                                                                                    Overall, we observed 14 canal switches (1.2%): 13 dur-
                                                                                    ing or after CRP (1.5%), one after QLR (0.6%), and none
                                                                                    after SM. (Fig. 3).
                                                                                    The statistical analysis was influenced both by the few
                                                                                    observed canal switches and the asymmetry of the groups;
 CRP: Canalith Repositioning Procedure; QLR: Quick Liberatory Rotation Manoeuver;   it did not show significant differences between the group
 SM: Semont Manoeuver.
                                                                                    treated with CRP vs. the group treated with either QLR or
Figure 1. Therapeutic manoeuvers primarily performed in our series.                 SM (p = 0.21).



                                                                                                                                                         51
L. Scotto di Santillo, L. Califano




                                                                                CRP: Canalith Repositioning Procedure; QLR: Quick Liberatory Rotation Manoeuver;
                                                                                SM: Semont manoeuver; LC: Lateral canal.



Figure 3. Posterior-lateral canal switch occurrence related to therapeutic manoeuvers.



Discussion                                                                      lar downbeat positional nystagmus evoked either in the
                                                                                anterior canal or the apogeotropic posterior canal BPPV.
Canal switch is a rare complication of therapeutic ma-                          An alternative hypothesis is the displacement of otoconia
noeuvers for posterior canal BPPV, already described                            above the utricular side of the cupula to a position that
by many authors. Otoconia can move from the posterior
                                                                                could provoke downbeat nystagmus 14. In a randomised
canal into either the lateral or the anterior canal during,
                                                                                trial, Yimtae et al. 15 reported the immediate shift poste-
immediately after a liberating manoeuver, or a few days
                                                                                rior canal-lateral canal BPPV in 2/29 cases (6.9%) treated
later.
                                                                                through CRP. The authors used up to five repetitions, pre-
Herdman et al. 13 described the switch from the posterior
                                                                                ceded by the immediate retest through the DH-T. They did
canal to the anterior canal in 2/85 cases treated with CRP
                                                                                not specify the time between each CRP and the retest that
(2.4%) and the switch from the posterior canal to the lat-
                                                                                could be a critical factor in the canal switches. Stenerson
eral canal in 3/85 cases observed three days after CRP had
                                                                                et al. 16 observed no canal switch in 607 cases of poste-
been performed (3.5%). The authors hypothesised that the
                                                                                rior canal BPPV treated through CRP, performing up to 4
entry into the lateral canal may occur in the supine posi-
                                                                                manoeuvers for each patient. The delay between CRP and
tion when the patient turns toward the affected side. They
                                                                                the retest was not indicated. White et al. 17 reported 15 pos-
did not exclude that the switch may occur during the ma-
                                                                                terior-lateral canal switches, not specified if geotropic or
noeuver, but the hypothesis was not supported by an im-
                                                                                apogeotropic, in 242 patients treated with CRP (6.2%). In
mediate retest. In our CRP series, we found the posterior-
                                                                                44 patients treated with CRP, Foster et al. 18 found 4 poste-
lateral switch in a much lower percentage (3/879: 0.34%).
                                                                                rior-lateral canal switches (geotropic form) (9.1%); in an-
For Herdman et al., the posterior-anterior canal switch
                                                                                other 4 cases (9.1%), they observed downbeat nystagmus,
would occur because of the direct passage of otoconia
                                                                                interpreted as due either to canal re-entry or otoconia per-
through the common crus. A personal interpretation that
                                                                                sistence in the non-ampullar arm of the affected posterior
also applies to the subsequent literature: downbeat nys-
                                                                                canal. The authors stated that the immediate reassessment
tagmus, considered the sign of the posterior-anterior canal
                                                                                through the DH-T performed less than two minutes after
switch, was actually caused by either the canal re-entry
                                                                                CRP could facilitate the canal switch; a 15-minute delay
or the persistence of small otoconial debris in the non-
                                                                                seemed sufficient to avoid it. Babic et al. 19 reported 41/162
ampullar arm of the posterior canal because of the simi-
                                                                                cases (25.3%) of either canal switch or canal re-entry: 39



52
                                                                                               Canal switch from posterior canal BPPV




from the posterior canal to the lateral canal, 24 in geotropic    delayed, i.e. observed at the follow-up visit, in 5 cases. The
form and 15 in apogeotropic form -lateral cupulolithiasis         re-entry frequency was inversely proportional to the time
according to the authors’ terminology, and 2 posterior ca-        of the immediate retest: no case was observed when the
nal re-entries. Switches did not occur during CRP but at the      retest was performed at least 5 minutes after the manoeu-
control through DH-T performed less than one minute after         ver. Similar to what reported by White 17, whose statements
CRP. The authors recommended a longer delay in recheck-           were accepted by Dispenza, patients who needed only one
ing patients. Their observation agrees with our data: our         manoeuver for resolution of the disease more frequently
low canal switch rate is probably also determined by the          showed an immediate canal re-entry, whereas delayed re-
15-minute delay between the therapeutic manoeuver and             entry was observed in patients who needed more than two
the retest. In 7/8 cases, either the switch or the canal re-en-   manoeuvers and who were sign-free at the first immediate
try occurred after a single successful CRP. Their hypothesis      control. The authors proposed a minimum time of 15 min-
was that large otoconial debris moved easily during the ma-       utes between the therapeutic manoeuver and retest. In this
noeuver, but could more easily cause canal re-entry. Lin 20       view, we did not consider downbeat positional nystagmus
highlighted that all canals, and not only the posterior ones,     evoked at the DH-retest as an expression of canal re-entry,
should be retested after CRP to recognise possible canal          but rather as a sign of small otoconial debris still present in
switches, since persistent symptoms would be caused by            the non-ampullar arm at the end of the manoeuver. Lacking
the secondary involvement of another canal in about 26%           in the oldest case-series a differential diagnosis between
of patients. The authors considered it necessary to maintain      anterior canal and apogeotropic posterior canal BPPV, we
a head extension of at least 30° below the horizontal plane       believe that in the past some of these forms could be inter-
during CRP. They also suggested that patients should not          preted wrongly as posterior-anterior canal switches.
be retested immediately after CRP, especially if no liberat-      Lee 24 reported 29/204 cases (2.4%) of posterior-lateral
ing nystagmus was detected. On the contrary, when we did          canal switch after CRP, 21 in geotropic form, 8 in apogeo-
not observe liberating nystagmus we think that it is pos-         tropic form. The authors performed a maximum of two
sible to immediately retest the patient since otoconia prob-      CRPs per session without reporting the time from CRP to
ably did not reach the utricle and, consequently, the risk of     the first control. Otoconia enter the common crus during
canal switch is almost null.                                      the manoeuver; if the neck is extended < 45° or the head
Park 21 reported posterior-anterior canal switches in             rotates > 45° in the final “nose-down” position 7 when
13/564 cases treated with CRP (2.3%). When the shift oc-          the patient returns to the sitting position, canaliths would
curred, the successful treatment of posterior canal BPPV          move from the common crus to the anterior canal.
required more manoeuvers than the cases without canal             We observed 14 canal switches in 1158 patients (1.2%):
switch (3.6 vs 1.6 manoeuvers), suggesting that canal             12 from the posterior to the lateral canal, 2 from the poste-
switch was a negative prognostic factor.                          rior to the anterior canal; no switch after SM (121 cases),
Anagnostou 22 observed posterior-lateral canal switch in          during or after CRP in 13/879 cases (1.5%), after QLR
4/51 cases treated with CRP (7.8%) and in none of 51 cases        in 1/158 cases (0.6%) (Fig. 3), without significant differ-
treated with SM. The prolonged position of the head in the        ences between CRP group vs. SM and QLR group.
extended position below the horizontal plane to a much            To avoid any undesirable effect, CRP should be performed
greater extent in CRP than SM would facilitate the entry          with accuracy, after adequate instructions to the patient.
of otoconial debris in the lateral canal across its utricular     She/he must not lift her/his head during the manoeuver;
opening, located next to the common crus exit. Switches           the return to the sitting position should be slow, keeping
occurred during CRP rather than at the retest, performed          the head bent forward by 20/30° and avoiding extension
between 2 and 5 hours later. If so, similar rates would be        movements that could compromise the success, causing
found even after SM. In our series, also, no patient treated      either the re-entry of otoconia into the affected canal or
with SM presented a canal switch. Shan 23 reported 2/135          the switch in the anterior or the lateral canal.
cases (1.5%) of posterior-lateral canal switch during a           Another relevant key point is the delay between each ma-
Computer-Controlled Repositioning Procedure. On the oth-          noeuver and retest through DH-T. We agree that a 15-min-
er hand, Dispenza et al. 12 observed weak positional down-        ute delay is sufficient to minimise the immediate canal
beat nystagmus at Dix-Hallpike retest due to ipsi-canalar         switch rate: in fact, we observed only 5 canal switches
reentry in 12/97 cases of posterior canal BPPV (12.4%)            at the 15-minute retest, all during or after CRP. The de-
treated either with SM or the so-called “hybrid” manoeu-          layed canal switches, posterior-lateral canal or posterior-
ver, corresponding to the QLR previously described by             anterior canal, could be caused by “casual” positions as-
Califano et al. 6. The re-entry was immediate in 7 cases and      sumed by patients during the lying-down position in the



                                                                                                                                 53
L. Scotto di Santillo, L. Califano




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                                                                                 2012;CD008675.          https://doi.org/10.1002/14651858.CD008675.
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The risk of canal switch is extremely low for any pro-                           of Otolaryngology-Head and Neck Surgery Foundation Clinical
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                                                                                 otohns.2008.08.022
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                                                                                 Califano L, Capparuccia PG, Di Maria D, et al. Treatment of be-
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                                                                                 Giannoni B, Marcelli V, Verdolin I, et al. Congruous torsional down
“nose-down” position, and the retest with DH-T at least                          beating nystagmus in the third position of the semont’s maneuver
after 15 minutes – can minimise the problem. At follow-                          in patients treated for canalithiasis of posterior semicircular canal
                                                                                 benign paroxysmal positional vertigo: its significance and prog-
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Conflict of interest statement                                              10
                                                                                 Epley JM. Human experience with canalith repositioning ma-
The authors declare no conflict of interest.                                     neuvers. Ann NY Acad Sci 2001;942:179-191. https://doi.
                                                                                 org/10.1111/j.1749-6632.2001.tb03744.x
Funding                                                                     11
                                                                                 Zanotti E,Yacovino DA. Benign paroxysmal positional vertigo: canal
This research did not receive any specific grant from                            switching affecting all canals during a single session. Otol Neurootol
                                                                                 2021;42:pe110. https://doi.org/10.1097/MAO.0000000000002853
funding agencies in the public, commercial, or not-for-                     12
                                                                                 Dispenza F, De Stefano A, Costantino C, et al. Canal switch and re-
profit sectors.                                                                  entry phenomenon in benign paroxysmal positional vertigo: differ-
                                                                                 ence between immediate and delayed occurrence. Acta Otolaryngol
Author contributions                                                             Ital 2015;35:116-120.
Both authors contributed equally to all the phases of the                   13
                                                                                 Herdman SJ, Tusa RJ. Complications of the canalith repositioning
                                                                                 procedure. Arch Otolaryngol Head Neck Surg 1996;122:281-286.
article (ideation, execution, design, analysis, drafting, revi-                  https://doi.org/10.1001/archotol.1996.01890150059011
sion).                                                                      14
                                                                                 Büki B. Benign paroxysmal positional vertigo. Toward new defi-
                                                                                 nitions. Otol Neurotol 2014;35:323-328. https://doi.org/10.1097/
Ethical consideration                                                            MAO.0000000000000197
As a retrospective observational study, it did not require                  15
                                                                                 Yimtae K, Srirompotong S, Srirompotong S, et al. A randomized trial
approval of Ethics Committee. This was done internally as                        of the canalith repositioning procedure. Laryngoscope 2003;113:828-
                                                                                 832. https://doi.org/10.1097/00005537-200305000-00011
part of our routine evaluation, so as to improve our qual-                  16
                                                                                 Steenerson RL, Gaye W, Cronin MHE, et al. Effectiveness of treat-
ity of care. The research was conducted ethically, with all                      ment techniques in 923 cases of benign paroxysmal positional ver-
study procedures being performed in accordance with the                          tigo. Laryngoscope 2005;115:226-231. https://doi.org/10.1097/01.
requirementsof the World Medical Association’s Declara-                          mlg.0000154723.55044.b5
tion of Helsinki.
                                                                            17
                                                                                 White J, Oas G. Diagnosis and management of lateral semicircu-
                                                                                 lar canal conversion during particle repositioning therapy. La-
                                                                                 ryngoscope        2005;115:1895-1897.       https://doi.org/10.1097/01.
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