10.14639/0392-100X-N1824
Objective. A mono-positional persistent, direction-fixed apogeotropic nystagmus (MPosApoNy) is very challenging for the neuro-otologist. MPosApoNy can be found in patients suffering from a partially compensated acute unilateral vestibulopathy; with a normal caloric test, one can speculate the presence of “trapped” otolithic debris located close to the ampulla of the horizontal semicircular canal. Methods. Among 957 patients suffering from vertigo and dizziness, we selected 53 cases of MPosApoNy. Results. In 28 patients, caloric test showed a canal paresis on the same side of the MPosApoNy. In the remaining 25 cases, MPosApoNy was the only clinical finding. We hypothesised the presence of horizonal canal lithiasis and patients were treated with a Gufoni manoeuvre, followed by a forced prolonged position. Conclusions. Performing bedside examination in a patient suffering from vertigo, the presence of MPosApoNy may be due to: a) facilitation of a subclinical nystagmus due to the mechanism of apogeotropic reinforcement; b) horizontal canal lithiasis with ‘trapped’ otoliths close to the ampulla. The disappearance of MPosApoNy following a repositioning manoeuvre or conversion in a typical form of canalolithiasis may represent the best method to confirm this hypothesis.
text/xml
1827-675X
1824
en
Augusto Pietro Casani
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
canalolithiasis
The clinical significance of direction-fixed mono-positional apogeotropic horizontal nystagmus: 
Text.Serial.Journal
https://www.actaitalica.it/
42
Vestibology
2022-06-30
2021-09-19
2022-07-26
2022-07-26
287-292
1
Augusto Pietro Casani
2022/06/30
10.14639/0392-100X-N1824
287
Department of Medicine and Surgery, ENT Section, Pisa University Hospital, Pisa, Italy
1827-675X
canalolithiasis
en
292
The clinical significance of direction-fixed mono-positional apogeotropic horizontal nystagmus: 
https://www.actaitalica.it/article/download/1824/834
42
ACTA OTORHINOLARYNGOLOGICA ITALICA 2022;42:287-292; doi: 10.14639/0392-100X-N1824




Vestibology


The clinical significance of direction-fixed
mono-positional apogeotropic horizontal nystagmus
Il significato clinico del nistagmo monoposizionale orizzontale apogeotropo
Mauro Gufoni, Augusto Pietro Casani
Department of Medicine and Surgery, ENT Section, Pisa University Hospital, Pisa, Italy


SUMMARY
Objective. A mono-positional persistent, direction-fixed apogeotropic nystagmus (MPosA-
poNy) is very challenging for the neuro-otologist. MPosApoNy can be found in patients
suffering from a partially compensated acute unilateral vestibulopathy; with a normal ca-
loric test, one can speculate the presence of “trapped” otolithic debris located close to the
ampulla of the horizontal semicircular canal.
Methods. Among 957 patients suffering from vertigo and dizziness, we selected 53 cases
of MPosApoNy.
Results. In 28 patients, caloric test showed a canal paresis on the same side of the MPosA-
poNy. In the remaining 25 cases, MPosApoNy was the only clinical finding. We hypoth-
esised the presence of horizonal canal lithiasis and patients were treated with a Gufoni
manoeuvre, followed by a forced prolonged position.
Conclusions. Performing bedside examination in a patient suffering from vertigo, the pres-
ence of MPosApoNy may be due to: a) facilitation of a subclinical nystagmus due to the
mechanism of apogeotropic reinforcement; b) horizontal canal lithiasis with ‘trapped’ oto-
liths close to the ampulla. The disappearance of MPosApoNy following a repositioning
manoeuvre or conversion in a typical form of canalolithiasis may represent the best method
to confirm this hypothesis.
KEY WORDS: benign paroxysmal positional vertigo, horizontal semicircular canal,
apogeotropic nystagmus, positional nystagmus, canalolithiasis                                    Received: September 19, 2021
                                                                                                 Accepted: March 25, 2022
RIASSUNTO
Obiettivo. Il riscontro di un nistagmo monoposizionale orizzontale apogeotropo (MPosA-           Correspondence
poNy) rappresenta una sfida diagnostica per il vestibologo. Tale nistagmo può indicare,          Augusto Pietro Casani
in presenza di un deficit al test calorico, una labirintopatia periferica non compensata. In     Department of Medicine and Surgery, ENT Section,
                                                                                                 Pisa University Hospital, via Paradisa 2, 56124
assenza di tale reperto, il MPosApoNy potrebbe essere riconducibile ad una forma atipica
                                                                                                 Pisa, Italy
di litiasi del canale semicircolare orizzontale (CSL).                                           Te. +39 050 997499
Metodi. Su 957 pazienti con vertigini, ne abbiamo selezionati 53 che presentavano MPosApoNy.     E-mail: augusto.casani@unipi.it
Risultati. In 28 pazienti il test calorico evidenziò un deficit ipsilaterale al MPosApoNy. Nei
rimanenti 25 in cui il test calorico risultò nella norma, si ipotizzò una litiasi del CSL con
otoliti intrappolati in prossimità dell’ampolla. Questi pazienti vennero trattati con manovra
di Gufoni e successiva posizione coatta.                                                           How to cite this article: Gufoni M, Casani
                                                                                                   AP. The clinical significance of direction-fixed
Conclusioni. Il riscontro di un MPosApoNy può riconoscere una duplice causa. Esso può
                                                                                                   mono-positional apogeotropic horizontal nystag-
essere l’espressione di un nistagmo subclinico esito di labirintopatia acuta monolaterale.         mus. Acta Otorhinolaryngol Ital 2022;42:287-
Tuttavia, la presenza di otoliti intrappolati in stretta vicinanza dell’ampolla ne può spie-       292. https://doi.org/10.14639/0392-100X-N1824
gare la genesi. In quest’ultimo caso, le manovre liberatorie, attraverso la risoluzione del
MPosApoNy o per la conversione in una forma tipica di canalolitiasi, possono confermarne         © Società Italiana di Otorinolaringoiatria
l’origine litiasica.                                                                             e Chirurgia Cervico-Facciale

PAROLE CHIAVE: vertigine parossistica posizionale benigna, canale semicircolare
                                                                                                                OPEN ACCESS
orizzontale, nistagmo apogeotropo, nistagmo posizionale, canalolitiasi
                                                                                                 This is an open access article distributed in accordance with
                                                                                                 the CC-BY-NC-ND (Creative Commons Attribution-Non-
Introduction                                                                                     Commercial-NoDerivatives 4.0 International) license. The
                                                                                                 article can be used by giving appropriate credit and mentio-
                                                                                                 ning the license, but only for non-commercial purposes and
Positional nystagmus is defined as a nystagmus triggered by and occurring                        only in the original version. For further information: https://
after a change in head position with respect to gravity 1. This nystagmus can                    creativecommons.org/licenses/by-nc-nd/4.0/deed.en




                                                                                                                                                         287
M. Gufoni, A.P. Casani




be transient (as in benign paroxysmal positional vertigo)        manoeuvers included lying down from sitting, head turning
or persistent: in the latter case the duration is long (gener-   to either side while supine (supine roll test), straight-head
ally > 1 minute) and the intensity is constant or slowly         hanging and Dix-Hallpike test. Caloric test was performed
decreases over time. The direction of persistent positional      according to a modified Fitzgerald–Hallpike technique.
nystagmus can be the same in both ear-down positions             The responses were recorded using an infrared eye-track-
(ipsiversive or unidirectional, fixed) or can change (con-       ing system (GN Otometrics, Taastrup, Denmark); canal pa-
traversive or bidirectional) 2. Occasionally, a persistent       resis (CP) was considered significant if > 25%. All patients
direction-fixed (ipsiversive) positional nystagmus can           underwent MRI investigation to rule out an involvement of
manifest only in one ear-down position. This behaviour           the central nervous system.
can be observed in patients suffering from acute unilateral
vestibulopathy in whom the spontaneous nystagmus con-            Results
tinues supine, but its intensity increases when the patient
lies on the affected side (affected ear down, homolateral        All 53 patients (32 males and 21 females age ranging from
excitation) and decreases on the opposite side (unaffected       20 to 84 years of age, mean 58 years) showed a persistent
ear up, contralateral inhibition) 3,4. As the vestibular tone    positional horizontal apogeotropic nystagmus in a single
imbalance causing spontaneous nystagmus progressively            position of the head (left or right side) during the supine
decreases (by means of the recovery of vestibular function       roll test and Dix-Hallpike test. In 21 patients there was an
or central vestibular compensation) until it disappears in       apogeotropic nystagmus on the left side, and in 32 patients
sitting position, when performing the positional test the        there was an apogeotropic nystagmus in the right side. In
nystagmus can appear only when the patient’s head is             28 of the 53 patients, caloric test showed a canal paresis
rotated to the affected side when supine (apogeotropic           on the same side of the apogeotropic persistent positional
reinforcement). This nystagmus will be positional, persis-       nystagmus; in all patients with canal paresis there was a
tent and present only on one side (mono-positional and           congruence between the side of reduced caloric response
apogeotropic) 5. Persistent positional nystagmus has also        and the side in which the positional nystagmus appeared.
been described (mostly bidirectional) in some central ves-       The head shaking test was positive with a peripheral pat-
tibular diseases such as vestibular migraine 6, more often       tern in 26 of 28 patients with canal paresis and in 4 patients
in association with other signs of central nervous system        with normal caloric test. In the remaining 25 cases, apo-
involvement. In some cases, a persistent ipsiversive po-         geotropic mono-positional nystagmus was the only clinical
sitional nystagmus (the nystagmus does not reverse its           and instrumental finding. In these cases, we hypothesised
direction with the supine roll test) may be attributed to        the presence of horizontal canal lithiasis and patients were
an atypical form of lateral canal benign paroxysmal posi-        treated with a Gufoni manoeuvre 8, followed by a forced
tional vertigo 7. In this paper, we retrospectively describe     prolonged position 9.
the characteristics of a population of patients suffering        After one session of treatment, 9 patients showed disap-
from vertigo showing a persistent horizontal apogeotropic        pearance of the positional nystagmus and in 5 cases a con-
mono-positional nystagmus.                                       version in a typical form of horizontal canal benign parox-
                                                                 ysmal positional vertigo (HC-BPPV, 4 apogeotropic and 1
Materials and methods                                            geotropic) occurred. In one case a canal switch towards an
                                                                 involvement of the posterior semicircular canal (PC-BPPV)
Among 957 patients admitted to our tertiary referral cen-        was evident. Five patients showed the disappearance of the
tre suffering from vertigo and dizziness in the period from      nystagmus after the second session of treatment and in two
January 2015 to December 2019, we selected 53 patients           cases a conversion in an apogeotropic form of HC-BPPV
showing a mono-positional apogeotropic horizontal nys-           was registered. The remaining 3 patients were instructed to
tagmus. The 53 patients came to our observation because          perform a series of home exercises consisting in four daily
of the onset of acute vertigo exacerbated or occurring after     sessions of head shaking test and barbecue manoeuvre. At
a change of head position in space relative to gravity. All      one-month follow-up, disappearance of the monopositional
patients, after careful assessment of clinical history, under-   persistence was evident (Fig. 1).
went a complete vestibular examination, consisting of the        Brain MRI showed normal results in all patients.
search for ocular alignment, spontaneous nystagmus, hori-
zontal and vertical gaze-holding nystagmus, head shaking
nystagmus, horizontal and vertical saccades, horizontal and
                                                                 Discussion
vertical smooth pursuit and head impulse test. Positional        We speculate that the presence of an apogeotropic posi-



288
                                                                                                         Mono-positional apogeotropic horizontal nystagmus




                                                                              latter, an apogeotropic mono-positional horizontal nystag-
                                                                              mus can be detected as the only expression of the imbal-
                                                                              ance of the two vestibular hemi-systems. In other terms,
                                                                              the position of the head reinforces the nystagmus, which
                                                                              becomes clinically evident. This condition can be easily
                                                                              confirmed by caloric tests, from which we expect a canal
                                                                              paresis, i.e. expression of the reduced function of one hori-
                                                                              zontal semicircular canal. Indeed, the results of the head
                                                                              shaking test were congruent (beating to the unaffected side)
                                                                              with the lesioned side in the majority of the 28 patients
                                                                              showing a canal paresis.
                                                                              The 25 cases in which the apogeotropic mono-positional
                                                                              horizontal nystagmus was not associated with canal paresis
                                                                              remain to be interpreted. An apogeotropic mono-positional
                                                                              nystagmus in the absence of signs of unilateral vestibular
                                                                              loss could be hypothetically considered as the consequence
                                                                              of a lateral canal lithiasis in which otolithic debris remain
                                                                              ‘trapped’ within the ampulla (Fig. 2). We can speculate that
                                                                              the dislocated otoliths are located close to the ampulla of
                                                                              the lateral semicircular canal (in our example on the right
                                                                              side) and are blocked in a cluster larger than the diameter of
                                                                              the channel (narrow part) and smaller than the diameter of
Figure 1. Summary of the results obtained with treatment in the 25 patients   the ampulla, with the result that the debris can move within
with monopositional apogeotropic horizontal nystagmus.                        the ampulla but cannot fall into the canal. If the patient as-
                                                                              sumes the right-side position when lying down, the debris
                                                                              must stop at the narrowest part of the canal. The movement
tional nystagmus in only one position may be due to two                       of the debris inside the ampulla is not able to generate a
pathological conditions:                                                      nystagmus 11; consequently, in the right side position no
1. an uncompensated unilateral vestibular loss;                               nystagmus can be elicited. When the patient turns the head
2. an atypical form of horizontal semicircular canal lithi-
   asis.
An apogeotropic mono-positional horizontal nystagmus
can be associated with a canal paresis, and in this case it
can be considered as the result of progressive improve-
ment of the imbalance between the two sides after unilat-
eral vestibular damage. A reduction of otolithic function on
the affected side might reinforce a spontaneous nystagmus
when the patient lies on the affected side3. In patients with
unilateral complete peripheral deafferentation, it is possi-
ble to observe an increase of the intensity of the spontane-
ous nystagmus when positioned on the affected side (the
nystagmus is apogeotropic) and a reduction of its intensity
when the patient lies on the healthy side (the nystagmus is
geotropic) 10. This phenomenon is related to asymmetric
                                                                              Figure 2. The apogeotropic monopositional nystagmus from ‘trapped’ oto-
macular activation due to unilateral macular damage. As                       lithic block. (A) The patient is in sitting position: the otolithic block is close to
vestibular compensation or spontaneous recovery progress,                     the right ampulla. (B) When the patient lies supine with the head rotated to the
the vestibular tone imbalance causing spontaneous nystag-                     right, the block does not provoke any cupular movement and no nystagmus is
mus progressively decreases; consequently, the nystagmus                      evident (the otolithic debris does not enter in the canal because of its dimen-
                                                                              sion (=).(C) When the patient lies supine with the head rotated to the left, the
can be seen only by moving the head (i.e., performing a                       movement of debris creates a persistent ampullopetal displacement of the cu-
Head Shaking Test) or performing the positional test. In the                  pula and a apogeotropic nystagmus appears (+).



                                                                                                                                                             289
M. Gufoni, A.P. Casani




to left side, the debris could induce an ampullopetal deflec-      • in the presence of a monopositional apogeotropic nystag-
tion of the cupula which provokes an excitatory nystagmus             mus, it is always advisable to complete the examination
directed to the right, and is apogeotropic because the pa-            with caloric tests. In the case of congruent dysreflexia, it
tient is positioned on the left side. The result is an apogeo-        is reasonable to interpret the nystagmus evoked as a fa-
tropic nystagmus evoked positioning the patient on the left           cilitated subclinical nystagmus. It is to be expected that,
side with no nystagmus in the opposite position. An origin            over time, the nystagmus tends to disappear along with
of the above-described positional nystagmus from a condi-             the improvement of the compensation and normalisation
tion of heavy/light cupula 12 seems to be less probable: usu-         of the directional preponderance;
ally this condition should cause a positional apogeotropic         • if the caloric test shows no canal paresis, an atypical
nystagmus when turning the head to the right side and to              form of HC-BPPV can be suspected. The hypothesis
the left side (bidirectional) when the patient lies in supine         is that the debris is in the horizontal canal on the side
position. The presence of otolithic deposits in atypical lo-          where no nystagmus is evoked. In case of modification
cations has already been described, namely the finding of             of the nystagmus after the manoeuvre (disappearance or
a paroxysmal nystagmus with fixed direction, apogeotrop-              conversion into a HC-BPPV or PC-BPPV), the diagno-
ic on the pathological side, and geotropic on the healthy             sis moves towards a form of ‘trapped’ ampullar lateral
side 7. The positional nystagmus recorded in our series of            canalolithiasis. We suggest performing the repositioning
patients differ from the latter because it appears in only one        manoeuvres even in the case of mild asymmetry of the
position of the head (right or left) when the patient lies su-        caloric response, especially if the patient reported a clin-
pine. Although a central origin of the apogeotropic posi-             ical history predominantly characterised by positional
tional nystagmus (monodirectional or bidirectional) cannot            vertigo. It is well known that the presence of a bulky
be excluded 13, our series of patients showed a normal brain          otoconial mass may be associated with mild hypofunc-
MRI. Our observations seem to suggest the possibility of a            tion of the HC.
very particular and not so common type of lithiasis of the         Finally, we must take in consideration that positional nys-
semicircular canal in which the debris are “trapped” close         tagmus (especially horizontal direction-changing apogeo-
to the ampulla, and unable to move into the narrow tract of        tropic or geotropic) may occur in up to 88% of healthy
the canal. This situation would be associated with a normal        subjects 20. Moreover, central nervous system involvement
caloric test, but a reduction of caloric response cannot be        could produce a positional nystagmus appearing mostly
ex ante excluded 14,15.                                            as downbeat nystagmus while prone or supine, or apogeo-
Based on this hypothesis, we tried to treat these patients us-     tropic or geotropic horizontal nystagmus when the head is
ing a combination of repositioning manoeuvres. The disap-          turned to either side while supine 13.
pearance of the apogeotropic mono-positional nystagmus             Our study has several limitations: firstly, not all patients
after performing one or two sessions of treatment, or its con-     were investigated using the video Head Impulse test, which
version in a feature compatible with a typical involvement of      could provide more information about the functionality of
the horizontal or posterior semicircular canal lithiasis, could    the two labyrinths at more physiological stimuli with re-
represent the confirmation of our hypothesis and could be the      spect to the caloric test; secondly, we do not have a control
best evidence for a differential diagnosis 16,17. In some cases,   group as in some normal subjects a positional nystagmus
the inefficacy of the repositioning manoeuvre could be due         can be detected. Furthermore, we assumed that modulation
to debris that has fallen into the short arm of the semicircular   of the spontaneous nystagmus due to a unilateral vestibu-
canal, as previously described 18. Recently, a high percentage     lar loss while performing the positional tests is related to
(38.7%) of patients suffering from Meniére’s disease showed        asymmetric macular activation due to the unilateral macu-
a monopositional apogeotropic nystagmus when turning the           lar damage; to confirm this hypothesis, a study of the utri-
head to the affected side. This observation could be related       cular and saccular function would be needed. Finally, we
to the comorbidity between Meniére’s disease and vestibular        did not perform cervical and ocular Vemps in all patients
migraine, conditions commonly characterised by the pres-           of our cohort. This could had prevented the discovery, al-
ence of a positional nystagmus 19. However, in our series          though very rare, of some type of positional nystagmus of
we excluded patients with clinical and instrumental findings       macular origin 21.
compatible with a definite diagnosis of Menière’s disease.
Based on the above-described observations, in a patient
complaining of vertigo and showing a monopositional apo-
                                                                   Conclusions
geotropic nystagmus, the diagnostic strategy could be set          When performing a bedside examination in a patient suf-
up as follows:                                                     fering from acute vertigo, the finding of apogeotropic mo-



290
                                                                                           Mono-positional apogeotropic horizontal nystagmus




nopositional nystagmus can be difficult to interpret. We          2
                                                                       Eggers SDZ, Bisdorff A, Von Brevern M, et al. Classification of ves-
                                                                       tibular signs and examination techniques: nystagmus and nystagmus-
suggest two possible diagnostic keys in order of clinical              like movements: consensus document of the Committee for the Inter-
frequency, as regards the differential diagnosis:                      national Classification of Vestibular Disorders of the Bárány Society.
1. facilitation of a subclinical nystagmus due to the mecha-           J Vestib Res 2019;29:57-87. https://doi.org/10.3233/VES-190658
   nism of apogeotropic reinforcement. In this case, it is        3
                                                                       Fluur E, Siegborn J. The otolith organs and the nystag-
                                                                       mus problem. Acta Otolaryngol 1973;76:438-442. https://doi.
   also possible to find a head shaking nystagmus directed             org/10.3109/00016487309121533
   in the same direction of the positional nystagmus, con-        4
                                                                       Wang H, Li Z, Zhang S, et al. Horizontal nystagmus is gravity-depend-
   gruent with the reduced activity of the HC as detected              ent in patients with vestibular neuritis. Am J Otolaryngol 2021;42:1-5.
   with the caloric test;                                              https://doi.org/10.1016/j.amjoto.2021.102967
2. HC-BPPV with ‘trapped’ otoliths close to the ampulla.
                                                                  5
                                                                       Roberts R, Gans R. Background, technique, interpretation, and use-
                                                                       fulness of positional/positioning testing. In: Jacobson G, Shepard N,
   The only method to confirm this hypothesis consists in              editors. Balance Function Assessment and Management. San Diego,
   performing a liberatory manoeuvre, assuming the side                CA: Plural Publishing Inc.; 2008. p.171-196
   where the nystagmus does not appear as the affected            6
                                                                       Young AS, Nham B, Bradshaw AP, et al. Clinical, ocu-
   side. The disappearance of this nystagmus or a conver-              lographic and vestibular test characteristics of vestibu-
                                                                       lar migraine. Cephalalgia 2021;41:1039-1052. https://doi.
   sion in a more common form of BPPV may represent the                org/10.1177%2F03331024211006042
   best method to confirm this hypothesis.                        7
                                                                       Califano L, Vassallo A, Melillo MG, et al. Direction- fixed paroxys-
                                                                       mal nystagmus lateral canal benign paroxysmal positioning vertigo
Acknowledgements                                                       (BPPV): another form of lateral canalolithiasis. Acta Otorhinolaryn-
                                                                       gol Ital 2013;33:254-260.
The authors thank Dr. Nicola Vernassa for the collection          8
                                                                       Casani AP, Nacci A, Dallan I, et al. Horizontal semicircular canal
and management of data.                                                benign paroxysmal positional vertigo: effectiveness of two different
                                                                       methods of treatment. Audiol Neurootol 2011;16:175-184. https://
                                                                       doi.org/10.1159/000317113
Conflict of interest statement
                                                                  9
                                                                       Mandalà M, Califano L, Casani AP, et al. Double-blind randomized
The authors declare no conflict of interest.                           trial on the efficacy of the forced prolonged position for treatment
                                                                       of lateral canal benign paroxysmal positional vertigo. Laryngoscope
Funding                                                                2021;131:e1296-1300. https://doi.org/10.1002/lary.28981
This research did not receive any specific grant from fund-       10
                                                                       Pagnini P, Vannucchi P, Nuti D. Il nistagmo spontaneo-posizionale:
                                                                       visione ortodossa o eterodossa? In: Atti X Giornata Italiana di Nistag-
ing agencies in the public, commercial, or not-for-profit              mografia Clinica. Milano: Formenti Ed 1990. p. 39
sectors.                                                          11
                                                                       Hain TC, Squires TM, Stone HA. Clinical implications of a mathe-
                                                                       matical model of benign paroxysmal positional vertigo. Ann NY Acad
Authors’ contributions                                                 Sci 2005;1039:384-394. https://doi.org/10.1196/annals.1325.036
MG: study concept and design, acquisition of data, analysis       12
                                                                       Tomanovic T, Bergenius J. Vestibular findings in patients with persis-
                                                                       tent geotropic positional nystagmus: the ‘light cupula’ phenomenon.
and interpretation of data, study supervision.                         Acta Otolaryngol 2014;134:904-914. https://doi.org/10.3109/000164
APC: study concept and design, analysis, and interpreta-               89.2014.928421
tion of data, drafting of the manuscript, study supervision.      13
                                                                       Choi JY, Kim JS. Central positional nystagmus: characteristics and
                                                                       model-based explanations. Prog Brain Res 2019;249:211-225. https://
                                                                       doi.org/10.1016/bs.pbr.2019.04.012
Ethical consideration                                             14
                                                                       Yetişer S, İnce D. Caloric analysis of patients with benign parox-
Ethical review and approval by the local Institutional Board           ysmal positional vertigo. J Int Adv Otol 2017;13:390-393. https://
(Comitato Etico Azienda Ospedaliero-Universitaria Pisana,              doi:10.5152/iao.2017.3312.
Pisa, Italy) were waived for this study. Due to its retrospec-    15
                                                                       Nuti D, Zee DS, Mandalà M. Benign paroxysmal positional vertigo:
tive nature, it was not considered as part of a research pro-          what we do and do not know. Semin Neurol 2020;40:49-58. https://
                                                                       doi.org/ 10.1055/s-0039-3402733
ject. Furthermore, the study does not include new invasive        16
                                                                       Casani AP, Dallan I, Berrettini S, et al. Therapeutic maneuvers in the
or experimental procedures or diagnostic protocol; all pa-             treatment of paroxysmal positional vertigo: can they indicate a central
tients underwent routinely performed tests only, according             genesis? Acta Otorhinolaryngol Ital 2002;22:66-73.
to national guidelines. Informed consent was obtained from        17
                                                                       Macdonald NK, Kaski D, Saman Y, et al. Central positional nystag-
                                                                       mus: a systematic literature review. Front Neurol 2017;8:141. https://
all participants and the study was performed in accordance             doi.org/10.3389/fneur.2017.0014
with the Declaration of Helsinki.                                 18
                                                                       Büki B, Mandalà M, Nuti D. Typical and atypical benign paroxys-
                                                                       mal positional vertigo: literature review and new theoretical con-
                                                                       siderations. J Vest Res 2014;24:415-423. https://doi.org/10.3233/
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