10.14639/0392-100X-N1032
The most common form of posterior canal benign paroxysmal positional vertigo (BPPV) is characterised by positional, paroxysmal, upbeat nystagmus, with a torsional component beating towards the downward ear. Rarer variants have been reported, putatively due to either the position of otoconia in the canal or anatomic variations of the semicircular canals. The most frequent less common form is apogeotropic posterior canal BPPV, in which the positional nystagmus is downbeat and torsional apogeotropic. In this form, the main problems are differential diagnosis with central mimics of BPPV and identification of the affected canal and its side. The authors propose a new subtype of apogeotropic posterior canal BPPV hypothesising the localization of otoconia in the ampullary tract of the affected canal, which might explain the modality of the conversion in typical posterior canal BPPV which they observed in some of these cases. If nystagmus of the less common forms of posterior canal BPPV is explicable through purely peripheral mechanisms, these forms should no longer be defined as “atypical” but, in a less demanding way, as “less common” variants, which must be recognised by any expert otoneurologist.
text/xml
1827-675X
1032
en
Giuseppe Manna
https://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
posterior canal BPPV less common variants
Less common forms of posterior canal benign paroxysmal positional vertigo
Text.Serial.Journal
https://www.actaitalica.it/
41
Vestibology
2021-07-07
2021-01-12
2021-07-08
2021-07-08
255-262
1
Giuseppe Manna
2021/07/07
10.14639/0392-100X-N1032
255
San Pio Hospital, Department of Audiology and Phoniatrics, Benevento, Italy
1827-675X
posterior canal BPPV less common variants
262
Less common forms of posterior canal benign paroxysmal positional vertigo
https://www.actaitalica.it/article/download/1032/624
41
ACTA OTORHINOLARYNGOLOGICA ITALICA 2021;41:255-262; doi: 10.14639/0392-100X-N1032




Vestibology


Less common forms of posterior canal benign
paroxysmal positional vertigo
Forme meno comuni di vertigine parossistica benigna da posizionamento
Luigi Califano, Salvatore Mazzone, Francesca Salafia, Maria Grazia Melillo, Giuseppe Manna
San Pio Hospital, Department of Audiology and Phoniatrics, Benevento, Italy




SUMMARY
The most common form of posterior canal benign paroxysmal positional vertigo (BPPV)
is characterised by positional, paroxysmal, upbeat nystagmus, with a torsional component
beating towards the downward ear. Rarer variants have been reported, putatively due to
either the position of otoconia in the canal or anatomic variations of the semicircular ca-
nals. The most frequent less common form is apogeotropic posterior canal BPPV, in which
the positional nystagmus is downbeat and torsional apogeotropic. In this form, the main
problems are differential diagnosis with central mimics of BPPV and identification of the
affected canal and its side. The authors propose a new subtype of apogeotropic posterior
canal BPPV hypothesising the localization of otoconia in the ampullary tract of the affected
canal, which might explain the modality of the conversion in typical posterior canal BPPV
which they observed in some of these cases. If nystagmus of the less common forms of pos-
terior canal BPPV is explicable through purely peripheral mechanisms, these forms should
no longer be defined as “atypical” but, in a less demanding way, as “less common” variants,     Received: January 12, 2021
which must be recognised by any expert otoneurologist.                                          Accepted: February 27, 2021

KEY WORDS: posterior canal BPPV, canalolithiasis, apogeotropic posterior canal BPPV,            Correspondence
posterior canal BPPV less common variants                                                       Luigi Califano
                                                                                                San Pio Hospital, Department of Audiology and
                                                                                                Phoniatrics, Benevento, Italy
RIASSUNTO                                                                                       via A. Lepore 1, 82100 Benevento, Italy
La forma più comune di vertigine parossistica posizionale benigna (VPPB) del canale po-         Tel. +39 0824 57407. Fax +39 0824 57430
steriore è caratterizzata da nistagmo posizionale, parossistico, verticale in alto, con com-    E-mail: luigi.califano@tin.it
ponente torsionale verso l’orecchio posizionato più in basso. Varianti meno comuni sono
presumibilmente dovute alla posizione degli otoliti nel canale o a variazioni anatomiche        Funding
dei canali semicircolari. La forma rara più frequente è quella apogeotropa, in cui il ni-       None.
stagmo posizionale batte verso il basso e la componente torsionale batte in opposizione
all’orecchio malato. In questa forma, i problemi principali sono la diagnosi differenziale      Conflict of interest
con le forme centrali di vertigine posizionale e l’identificazione del canale e lato interes-   The Authors declare no conflict of interest.
sati.Gli autori propongono un nuovo sottotipo di VPPB apogeotropa del canale posteriore,
ipotizzando la localizzazione degli otoconi nel tratto ampollare del canale interessato, il       How to cite this article: Califano L, Mazzone S,
che potrebbe spiegare la modalità della conversione in forma tipica del canale posteriore         Salafia F, et al. Less common forms of posterior
osservata in alcuni di questi casi. Se il nistagmo delle forme meno comuni di VPPB del ca-        canal benign paroxysmal positional vertigo. Acta
nale posteriore è spiegabile attraverso meccanismi periferici, queste forme non dovrebbero        Otorhinolaryngol Ital 2021;41:255-262. https://
più essere definite come “atipiche” ma, in modo meno impegnativo, come varianti “meno             doi.org/10.14639/0392-100X-N1032
comuni” la cui conoscenza è richiesta all’Otoneurologo esperto.
                                                                                                © Società Italiana di Otorinolaringoiatria
PAROLE CHIAVE: VPPB da canalolitiasi posteriore, canalolitiasi, VPPB da canalolitiasi           e Chirurgia Cervico-Facciale
posteriore apogeotropa, varianti meno comuni di VPPB da canalolitiasi posteriore
                                                                                                               OPEN ACCESS

                                                                                                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
The topographical classification of benign paroxysmal positional vertigo (BP-                   only in the original version. For further information: https://
PV) is based on the position of otoconia in the semicircular canals, which can                  creativecommons.org/licenses/by-nc-nd/4.0/deed.en




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L. Califano et al.




hypothetically be inferred through the oculomotor respons-                       sits up from the Dix-Hallpike position on the affected side;
es observed during positioning tests and determined by the                       5. Posterior canal heavy cupula 8 caused either by otoconia
endolymphatic flow induced in the affected semicircular                          attached to the cupula -cupulolithiasis- or by a transitory
canal. According to Ewald’s laws, in the vertical canals,                        modified density ratio between the cupula and the sur-
ampullofugal flow is excitatory and ampullopetal flow is                         rounding endolymph. 6. Posterior canal light cupula 9-11,
inhibitory, whereas the opposite occurs in the lateral ca-                       characterised by a cupula with a specific gravity lower than
nals. Ampullary responses to endolymphatic flow cause the                        the endolymph. 7. Yetiser’s variant 12, characterised by a
activation/inhibition of the extra-ocular muscles, which are                     biphasic paroxysmal nystagmus, whose first phase presents
anatomically connected to the vestibular system through a                        a torsional component reversed respect to the side of stimu-
neural circuitry that mediates the vestibulo-oculomotor re-                      lation.
flex. Thus, the coordinated responses of extra-ocular mus-                       Our retrospective cohort study analysed the frequency
cles evoke nystagmus in predictable ways.                                        of the so-called atypical forms of posterior canal BPPV,
In the typical form of posterior canal BPPV (TPC), posi-                         their response to physical therapy and their evolution.
tioning test evokes paroxysmal nystagmus with fast phas-                         Data from the most frequent of them, the apogeotropic
es directed towards the upper ocular pole for the vertical                       form, the only one which was susceptible to numerical
component and towards the downward ear for the torsional                         analysis, were examined. We also considered its mode-
component (“geotropic” form) 1 (Fig. 1).                                         ling and the modalities of its possible conversion in TPC,
Less common clinical variants of posterior canal BPPV                            finally hypothesising a new possible subtype of this form.
have also been reported: 1. “Reversed posterior canal BP-                        We will also provide critical analysis of the rarest forms
PV”, 2,3 characterised by downbeat and torsional nystagmus                       of posterior canal BPPV.
beating towards the inferior ocular pole and the upward ear
(apogeotropic nystagmus); 2. “Short arm canalolithiasis”                         Patients and methods
in which otoconia are in the utricular arm of the posterior
ampulla 4; 3. Subjective BPPV and Type 2 BPPV 5,6 : during                       From January 2019 to February 2020 we observed 630
the positioning tests, some patients experience only subjec-                     cases of acute BPPV: 466 TPC, diagnosed and treated ac-
tive symptomatology without positional nystagmus (sub-                           cording to current diagnostic and therapeutic guidelines 1,
jective BPPV). In returning to the sitting position, they feel                   25 apogeotropic variant of posterior BPPV (APC) and 4
a short and intense dizzy sensation accompanied by a sense                       anterior canal BPPV (AC), for a total of 29 cases of posi-
of retropulsion, up to almost falling in some cases; 4. Sit-                     tional downbeat nystagmus (PDN), 5 cases ascribable to
ting Up Vertigo 7 , in which positional vertigo and position-                    Scocco’s variant, 2 cases ascribable to Yetiser’s variant and
ing nystagmus typical of TPC is evoked when the patient                          128 lateral canal BPPV. We used criteria set out in a previ-
                                                                                 ous paper 13 to distinguish between AC and APC, maintain-
                                                                                 ing their classification in three grades (Tabs. I, II). In the
                                                                                 same period, we observed 34 central PDNs that will not
                                                                                 be the object of our presentation. Another 25 cases were
                                                                                 ascribed to either “subjective BPPV” (10 cases) or “trunk
                                                                                 retropulsion in sitting up without observable nystagmus”
                                                                                 (15 cases). Patients underwent otomicroscopy, pure tone
                                                                                 audiometry and infrared videonystagmoscopy. Video head
                                                                                 impulse test (v-HIT) was performed in 205 patients. The
                                                                                 diagnosis of vertical canal BPPV was based on the Dix-
                                                                                 Hallpike test and head hanging positioning. After informed
                                                                                 consent, 466 TPC cases were treated through quick libera-
                                                                                 tory rotation manoeuver (QLR) 14, Epley manoeuver or Se-
                                                                                 mont manoeuver; 25 APC cases were treated either through
                                                                                 QLR or through Vannucchi manoeuver 15. Brain MRI was
                                                                                 planned in APC and AC “possible” forms. Scocco’s vari-
                                                                                 ant cases were treated through QLR, Epley manoeuver and
                                                                                 Brandt-Daroff protocol. Yetiser variant cases were treated
Figure 1. During the positioning test otoconia (blue circles) move ampullo-
phugally in typical posterior canal BPPV (on the left), move ampullopetally in   through QLR; “Subjective BPPV” cases were treated and
apogeotropic posterior canal BPPV (on the right).                                resolved through a liberatory manoeuver – QLR, Epley ma-



256
                                                                                                                         Less common forms of posterior canal BPPV




Table I. Anterior canal BPPV.
 a) Definite AC BPPV
 Presence of a positional vertical down-beating paroxysmal nystagmus evoked through the straight head-hanging positioning and sometimes through the Dix-
 Hallpike test
 In such positions, possible presence of a slight clockwise torsional component for the left AC or of a slight counterclockwise torsional component for the right
 AC
 Canal conversion in typical posterior canal BPPV during or immediately after (no more than two days) the therapeutic manoeuvre, characterised by a vertical
 up-beating nystagmus, clockwise for the left canal and counterclockwise for the right canal
 b) Probable AC BPPV
 As reported in Ia, but with a direct resolution of disease without canalar conversion in typical posterior canal BPPV
 c) Possible AC BPPV
 Persistence of symptoms after 5 cycles of therapeutic manoeuvres
 MRI does not show any neurological disease as a presumed cause of the nystagmus
 or
 Patient lost to follow-up before the resolution of the disease
AC: anterior canal; BPPV: benign paroxysmal positional vertigo; MRI: magnetic resonance imaging.



Table II. Apogeotropic posterior canal BPPV.
 a) Definite APC BPPV
 Presence of torsional apogeotropic nystagmus, evoked through the Dix-Hallpike test and sometimes through the straight head hanging positioning
 Presence of a vertical down-beating component in the same positioning tests
 Canalar conversion in typical posterior canal BPPV during or immediately after (no more than two days) the therapeutic manoeuvre, or suddenly during the
 prolonged maintenance of one of the head hanging positions (straight head hanging; “deep” Dix-Hallpike position) or during the maintenance of leaning
 position in sitting position
 b) Probable APC BPPV
 As reported in IIa, but with a direct resolution of disease without canalar conversion in typical posterior canal BPPV
 c) Possible APC BPPV
 Persistence of symptoms after 5 cycles of therapeutic manoeuvres
 MRI does not show any neurological disease as a presumed cause of the nystagmus
 or
 Patient lost to follow-up before the resolution of the disease
APC: apogeotropic posterior canal; BPPV: benign paroxysmal positional vertigo; MRI: magnetic resonance imaging.



noeuver or Semont manoeuver – performed starting from                                      Results
the side of the referred symptoms; “Trunk retropulsion
                                                                                           BPPV cases accounted for 24.8% of all vertiginous and
in sitting up without observable nystagmus” cases were
                                                                                           dizzy patients we observed in the same period, represent-
treated through a home protocol, derived from the original
                                                                                           ing the first cause of vertigo in our series. In our geographic
proposal by Büki et al. 5, based on the repetition of Dix-
                                                                                           area, BPPV incidence was 132/100,000 per year.
Hallpike positioning followed by the return in the sitting                                 APC represented 5.02% of the overall acute posterior ca-
position for 10 consecutive times, three times a day for                                   nal BPPV cases (25 out of 498 cases), much more frequent
seven consecutive days.                                                                    than AC (4 cases) (ratio APC/AC: 6.25/1). In 21/29 cases of
Our analysis focused mainly on the diagnosis, treatment                                    peripheral PDN, positional vertigo caused by movements in
and modelling of APC cases, the only “atypical” group                                      the pitch plane was the main symptom. Four patients report-
susceptible to numerical analysis. Statistical analysis was                                ed only sub-continuous dizziness and intolerance to move-
performed with descriptive statistics and confidence inter-                                ments. In the APC group, the mean age was 58.6 ± 10.34,
val of a mean, and unpaired T-test, with significance level                                the female/male ratio = 1.32, which was not significantly
set at 0.05, 95% confidence interval, using the Graph pad                                  different from the overall posterior canal BPPV population
Quick Calcs software.                                                                      (mean age 59.6 ± 7.45, female/male ratio = 1.36).
All procedures were in accordance with the ethical stand-                                  463/466 cases of TPC were resolved through QLR, or Ep-
ards of the Ethics Review Board and with the 1964 Hel-                                     ley manoeuver, or Semont manoeuver; the mean number
sinki declaration and its later amendments.                                                of liberatory manoeuvers needed to cure was 2.07 ± 0.79



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L. Califano et al.




(range 1-5), without significant differences between the           tagmus. In the past, such forms were “tout-court” defined
three manoeuvers.                                                  as atypical. Epley 16 considered atypical all forms of posi-
12 APC cases were treated through QLR, 6 cases through             tional vertigo whose evoked nystagmus did not respect the
Vannucchi manoeuver and 1 case through both QLR and Van-           usual patterns. Rarer variants of posterior canal BPPV do
nucchi manoeuver; 6 cases were converted in TPC through            exist and are sustained by various clinical observations 2-13.
the maintenance of a hyperextension position of the head, and      They are explained either by anomalous localisation of oto-
then treated through QLR (see later). The direct resolution        conia in different tracts of the affected posterior canal or by
of APC (one step therapy, “probable” grade) was obtained           anatomical anomalies or structural changes of semicircular
in 10/25 patients (40%), in 7 cases through QLR, in 3 cases        canals, such as stenosis and fibrosis, as high definition MRI
through Vannucchi manoeuver. The mean number of QLR in             and micro-CT three-dimensional reconstruction have sug-
the one-step therapy was 2.71 ± 0.95, which was significantly      gested 17,18. In the above-mentioned situations, movements
higher than in TPC (p = 0.03). APC converted in TPC (“defi-        of otoconia causing endolymphatic flows different from the
nite grade”) in 14/25 cases (56%): in 5 cases through QLR,         typical ampullofugal current occurring in TPC during po-
in 3 cases through Vannucchi manoeuver, in 6 cases suddenly        sitional tests are believed to occur: for example, ampullo-
and intensely during the prolonged maintenance of a forced         petal flow in APC, or ampullofugal flow in sitting-up in
head hyperextension position: head hanging position in 2           Scocco’s variant.
cases, Dix-Hallpike position on the affected side in 3 cases,      1. “Reversed posterior canal BPPV” is characterised by
leaning position in 1 case, sometimes without any dynamic          downbeat and torsional nystagmus beating towards the in-
movement, in a time ranging between 45 seconds and 5 min-          ferior ocular pole and the upward ear (apogeotropic nys-
utes, and sometimes after a facilitating technique, i.e. a rapid   tagmus). This form is associated with otoconia displaced in
bowing of the head followed by hyperextension in “deep”            the non-ampullary tract of the posterior canal 2,3,13. During
Dix-Hallpike or head hanging position. The mean number of          diagnostic tests, otoconia move away from the non-amp-
QLR and Vannucchi manoeuvers necessary to convert APC              ullary tract of the posterior canal and provoke an ampullo-
into TPC was 2.26 ± 0.81. One case (4%) with negative brain        petal endolymphatic flow in the affected canal (Fig. 1).
MRI failed the treatment (“possible” grade).                       This causes the inhibitory response of the ampullary recep-
All APC cases converted in TPC were then cured through             tor that evokes both the vertical downbeat vector and the
QLR (two-step therapy), by a mean number of manoeuvers             torsional component of the positional nystagmus. Vannuc-
of 2.46 ± 0.88, which was slightly significantly higher than       chi called this clinical scenario “apogeotropic posterior ca-
in TPC cases (p = 0.05).                                           nal BPPV” (APC) 3. In APC, nystagmus is usually evoked
Three AC cases were solved through Yacovino manoeuver,             in both Dix-Hallpike positions and head hanging position.
1 case was not resolved, and treated through Brandt-Daroff         It seldom reverses in returning to the sitting position. Nys-
home protocol.                                                     tagmus is caused by the activation of the same ocular mus-
In a 3-17 month follow-up, last evaluation in May 2020,            cles activated in contralateral anterior canal BPPV (AC),
2 patients of the peripheral PDN group relapsed in ipsilat-        ipsilateral superior rectus muscle and contralateral inferior
eral TPC, 1 in ipsilateral APC and 1 in ipsilateral geotropic      obliquus, so the differentiation between the two forms is
lateral canal BPPV. No patient showed signs and/or symp-           sometimes difficult 3,13.
toms of neurological disease.                                      Büki 6 provided another interesting explanation of at least
All the cases of both “subjective BPPV” and “trunk retropul-       some cases of PDN from posterior canalolithiasis. If de-
sion in sitting up without observable nystagmus” were char-        tached otoconia enter the common crus or if the patient lib-
acterised by a significant delay in diagnosis and treatment,       erates himself by turning over in bed, or if otoconia detach
in all cases more than 40 days from the onset of acute and         when the patient is standing, otoconia remain or return into
typical symptoms which have progressively disappeared.             the utriculum. Here, they may be re-located in the pericupu-
“Subjective BPPV” cases were resolved through 1.40 ± 0.52          lar short arm and fall on the posterior canal cupula which, in
therapeutic manoeuvers; “trunk retropulsion in sitting up          the upright position, is just below the utricular macula. The
without observable nystagmus” cases were resolved through          cupula of the posterior canal would adapt itself to the greater
one cycle of the above described home protocol.                    weight present on it, chronically deflecting itself downward.
                                                                   In these cases, in either the Dix-Hallpike position or the head
                                                                   hanging position, nystagmus may not be evoked. If evoked,
Discussion                                                         it is downbeat, slight, and long-lasting. This is determined
Some forms of presumed posterior canal BPPV are char-              both by the spatial orientation of the cupula, which is now a
acterised by nystagmus that is different from the TPC nys-         graviceptive organ and by its upward displacement.



258
                                                                                           Less common forms of posterior canal BPPV




The main problem when observing a PDN is its possible             Afterwards, due to gravitational force, otoconia slide back
origin from a central, particularly cerebellar, disease 19-21.    ampullofugally towards the narrow tract evoking a “coun-
In these cases, nystagmus is not provoked by otoconia in a        ter-positioning“ nystagmus analogous in its characteristics
semicircular canal but by impaired “central vestibular pro-       to the TPC nystagmus usually evoked in the ipsilateral Dix-
cessing of canal and otolith in addition, to prolonged veloc-     Hallpike position. This variant is often resistant to reposi-
ity storage in the cerebellar nodulus” 20. In central PDN,        tioning manoeuvres: in fact, the authors always resolved
further central ocular motor abnormalities are usually pre-       their cases through Brandt-Daroff home protocol.
sent. Other important criteria for the differential diagnosis     5. Yetiser 12 described a single case of paroxysmal nystag-
are the conversion of the peripheral PDN in TPC and/or its        mus evoked by the Dix-Hallpike test on the left side. Nys-
resolution through a liberatory manoeuvre. In all the other       tagmus was biphasic: after a short latency, its first phase
cases, brain MRI is mandatory.                                    was paroxysmal, upbeat and counterclockwise, immediate-
2. Oas 4 hypothesised the “short arm canalolithiasis” in          ly followed by a second phase, upbeat and clockwise, with
which otoconia are in the utricular arm of the posterior          lower intensity and longer duration. The author concluded
ampulla. After the paroxysmal phase of the positional nys-        that nystagmus would be caused by canalolithiasis of the
tagmus has ended, the short arm canalolithiasis provokes          non-ampullary arm of the left posterior canal. The second
a slight and persistent ipsidirectional torsional nystagmus;      phase of the nystagmus would be due to the ampullofugal
differently, in the typical form – long arm canalolithi-          reflux of the endolymph after the initially evoked ampullo-
asis – a transient reversed torsional nystagmus happens.          petal flow.
During the repositioning manoeuvre, instead, the short arm        6. Posterior canal heavy cupula 8. This condition would
canalolithiasis would be characterised by the reversal of the     be caused either by otoconia attached to the cupula – cu-
nystagmus. The author proposed an “ad hoc” therapeutic            pulolithiasis – or by a transitory modified density ratio
protocol for such a form.                                         between the cupula and the surrounding endolymph. The
3. Subjective BPPV and Type 2 BPPV 5,6. The authors ob-           second situation is typically observed in migraineurs with
served 200 consecutive patients from 3 to 5 months after          frequently recurrent spells of positional vertigo (migraine-
the onset of positioning vertigo, reporting a TPC in 19.5%.       related positional vertigo). The density of the endolymph
During the positioning tests, 43% of patients experienced         would be modified by metabolic changes due to migraine
only subjective symptomatology without positional nystag-         attacks, e.g, localised fluid diffusions from the labyrinth
mus (subjective BPPV). In returning to the sitting position,      microcirculation to the endolymph. Posterior cupulolithia-
they felt a short and intense dizzy sensation accompanied         sis and heavy cupula from pericupular light endolymph are
by a sense of retropulsion, up to almost falling in some cas-     just slightly different from canalolithiasis in the features of
es. In about 50% of these cases, patients reported abnormal       the evoked positional nystagmus: quick phase direction is
trunk oscillations which were objectively quantified by an        similarly geotropic, upbeat and rotatory towards the down-
“ad hoc” posturography in the sitting position. The authors       most ear, but the nystagmus has short or no latency, is less
called this form ”Type 2 BPPV”, caused by the presence of         paroxysmal, longer-lasting and less fatigable. Liberatory
free-floating otoconia in the utriculus near the posterior ca-    manoeuvres are not effective in heavy cupula from light
nal cupula. Otoconia produced neither significant cupular         endolymph; instead, physical therapy works better in cu-
displacement nor nystagmus in the Dix-Hallpike position-          pulolithiasis, and mastoid vibration can help to detach oto-
ing. When patients returned to the sitting position, otoconia     conia from the cupula. Because the evoked nystagmus is
floated in the short arm causing dizziness, sometimes with        the same as TPC, albeit longer-lasting and less paroxysmal,
compliant of retropulsion. The authors proposed repetitive        in our analysis we will not consider this form as “atypical”.
sits-up from the Dix-Hallpike position as liberatory ma-          7. Posterior canal light cupula 9-11. “Light cupula” is char-
noeuvre.                                                          acterised by a cupula with a specific gravity lower than the
4. Scocco et al. 7 described positional vertigo and position-     endolymph. It is described in the first phase of post alco-
ing nystagmus typical of TPC but evoked when the patient          hol nystagmus (positional direction-changing nystagmus).
sits up from the Dix-Hallpike position on the affected side       Ichimura et al. 16 reported a case of a 16-year-old boy with
(Sitting Up Vertigo). They often observed this variant after      rotatory positional vertigo visited on the next day after
a repositioning manoeuvre. Either a narrowing of the canal        symptoms onset. The authors observed persistent position-
in the periampullary arm or large-sized debris block otoco-       al down-beating and rotatory nystagmus with the fast phase
nia to move distally in the Dix-Hallpike positioning. When        beating towards the left ear both on the right head roll test
the patient returns quickly to the sitting position, during the   and the right Dix-Hallpike test. Symptoms and signs dis-
movement, otoconia move inertially towards the cupula.            appeared in five days without any treatment. The authors



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L. Califano et al.




proposed that nystagmus occurred because of light cupula          es: in 8/14 cases (57.1%) after a liberatory manoeuver; in
of the right posterior canal. Head roll test and Dix-Hallpike     6/14 cases (42.9%) suddenly and intensely during the pro-
test on the right side would cause the ampullopetal deflec-       longed maintenance of a forced head hyperextension posi-
tion of the right posterior canal cupula, provoking an in-        tion, sometimes without any dynamic movement applied
hibitory response with fast phases directed downward and          to patients’ heads, sometimes after a facilitating technique
towards the left ear. Either light debris attached to the cu-     (see above). Both the conversion in TPC and the direct
pula, such as blood cells 16, or the increase of the density of   resolution through a liberatory manoeuver are compatible
the pericupular endolymph could cause light cupula 17. Pos-       with otoconia dislodged in the non-ampullary arm of the
terior canal light cupula would be rarer than lateral canal       affected posterior semicircular canal. Instead, the critical
light cupula because light debris drops off easier into the       conversion through a prolonged still position does not ap-
ampulla of the lateral canal, which is in a higher position       pear compatible with non-ampullary arm canalolithiasis.
than the ampulla of the posterior canal.                          In fact, the sudden fall of otoconia from this zone would
Recently, Kim proposed another possible mechanism of              provoke an ampullopetal endolymphatic flow, therefore
light cupula caused by the difference in density between          evoking a downbeat and torsional apogeotropic nystagmus
perilymph and endolymph. “When the density of perilymph           once again. The observed nystagmus can only be justi-
becomes higher than that of endolymph by any cause, the           fied by an ampullofugal movement of otoconia from the
membranous canal containing endolymph becomes buoy-               periampullary zone to the most declivous part of the canal
ant within the perilymphatic space under the constant influ-      (Ewald’s II law). A putative anomalous slope of the corre-
ence of gravity” 22.                                              sponding canal tract would initially cause an ampullopetal
Apogeotropic posterior canal BPPV is considered the most
                                                                  endolymphatic flow in the diagnostic position (Fig. 2B). At
frequent posterior canal BPPV variant. It is also defined
                                                                  some point, either the prolonged maintenance of a forced
as reversed posterior canal BPPV because of the downbeat
                                                                  head hyperextension position or the facilitating technique
and torsional nystagmus towards the upward ear 2,3,13. The
                                                                  described above (Fig. 2C) could lead otoconia to move to-
two most accredited hypotheses are either otoconia in the
                                                                  wards the area of a canal counter-slope, determining their
non-ampullary arm of the canal or otoconia dislodged in
                                                                  ampullofugal sliding (Fig. 2D). Theoretically, nystagmus
the short arm, in the utricular side of the cupula.
                                                                  could also be caused by the exit of otoconia from the poste-
In a recent multicentre study through v-HIT, Castellucci
                                                                  rior canal (“liberatory” nystagmus). This circumstance was
et al. 23 demonstrated a decrease of the VOR gain of the
affected canal in 72.9% of 59 cases of PDN, either from           denied because TPC nystagmus was still present at the im-
APC or from AC, increasing up to 88.6% in the subgroup            mediate retest by the Dix-Hallpike positioning: this means
with persistent down beat nystagmus, either positional or         that otoconia, were still dislodged in the affected canal.
spontaneous. This datum was useful to distinguish between         The observed nystagmus suggested the existence of at least
APC and contralateral AC. The authors suggested a partial         two subgroups of APC: 1. otoconia are in the non-ampul-
jam of the affected canal as the mechanism of the disease.
A partial canal jam might determine impaired responses
for high-frequency stimuli, such as head impulses in v-
HIT, whereas low-frequency stimuli, such as the cupular
stimulus of the endolymph flow activated during the posi-
tional test, remain active (low-pass filter). Data reported by
Castellucci et al. 23 highlight the difference between APC              A                                        B
and TPC, in which the posterior canal VOR gain is not af-
fected 24.
As we pointed out in a previous paper 13, only the conver-
sion in TPC leads us to diagnose a definite APC. In that
study, we analysed the oculomotor patterns of peripheral
                                                                        C                                        D
PDN and observed that APC was more common than AC.
Our current clinical confirmed these data: APC represents
a rare but not exceptional observation – 5% of all posterior      Figure 2. Our new model for some forms of apogeotropic posterior canal
                                                                  BPPV. Otoconia (blue circle) are in the periampullary tract of the posterior ca-
canal BPPV – and it is much more frequent than AC – 25            nal (A). During the Dix-Hallpike test they move ampullopetally (B). A quick and
vs 4 cases (ratio APC/AC = 6.25).                                 limited bowing of the head (C) followed by head hyperextension cause otoconia
We observed the conversion of APC in TPC in 14/25 cas-            to move ampullophugally as in typical posterior canal BPPV (D).



260
                                                                                                 Less common forms of posterior canal BPPV




lary arm; 2. otoconia are in the periampullary zone of the         the conversion in TPC of the contralateral posterior canal,
canal.                                                             in theory not examined through the positioning test on the
During the diagnostic phase, in both cases otoconia move-          other side. Could the different orientation of the affected
ments provoke an ampullopetal, inhibitory endolymphatic            semicircular canal, that would make it more susceptible to
flow, but only the periampullary position of otoconia could        stimulation in contralateral positioning, be the hypothetical
explain the sudden appearance of TPC nystagmus through             anomaly causing this variant? It could, but it should be not-
a prolonged head hyperextension position. Otoconia in the          ed that, in both our cases, the affected canal was activated
non-ampullary tract, near the common crus, but also otoco-         on its proper side positioning, causing the disappearance of
nia on the utricular side of the cupula, which could explain,      a nearly anecdotal variant!
in some of our cases, the direct resolution of canalolithiasis     “Subjective BPPV” and “trunk retropulsion in sitting up
through liberatory manoeuvers.                                     without observable nystagmus” represented a not rare pos-
Compared to the position stated in our previous article 13,        sible evolution of non treated cases because of either the
we are in fact currently more inclined to consider Büki ‘s         delayed diagnosis or a not entirely resolutive therapy. The
model 5,6 to explain some of the cases with the direct resolu-     response to physical therapy was good.
tion of APC (“probable“ grade). In our opinion, this possi-
bility, however, is more plausible for long-lasting, untreat-
                                                                   Conclusions
ed or not successfully treated cases.
A slight and transitory downbeat apogeotropic positional           The interpretative schematism of posterior canal BPPV
nystagmus is sometimes observed immediately after the              and, in particular, the idea that all cases of positional down-
treatment of TPC. It is probably determined by otoconial           beat nystagmus are due to central neurological diseases,
debris still present in the extreme distal portion of the ca-      have been lost 19,20,21,26.
nal 25. This observation does not configure an autonomous          Less common subtypes of BPPV, hypothetically due to a
variant, but, instead, indirectly confirms the hypothesis that     non-standard position of otoconia in the affected canal, or
in APC otoconia could be dislodged in the non-ampullary            canal anomalies, or partial canal jam, are possible. Their
tract of the canal.                                                interpretations are suitable only if they agree with Ewald’s
Scocco 7 considered the periampullary position of otoconia         laws: if they do, the observed nystagmus pattern has to be
in his variant, as well. He hypothesised canal stenosis of the     considered compatible with peripheral mechanisms. There-
distal periampullary tract and/or large-sized debris which al-     fore, in a less demanding way, the less common posterior
low otoconia to move ampullophugally from the periampul-           canal BPPV types must be considered as “variant forms”
lary zone to the stenosis not through the Dix-Hallpike test but    and no longer defined as “atypical forms”.
returning to the sitting position. In our current series, we ob-   In the spirit of what Epley wrote 16, the more different a
served 5 similar cases. Our approach and their clinical evolu-     nystagmus is from the most common nystagmus observed
tion were the same that Scocco reported. Therefore, we agree       in that disease, the more likely other diseases could be its
with his model, which fully respects Ewald’s laws.                 cause. The less common variants of posterior canal BPPV
The model proposed by Yetiser 12 – non ampullary arm               require an in-depth clinical study to detect any signs of cer-
canalolithiasis to explain a demi-reversed form of left pos-       ebellar diseases. Careful neurotological examination may
terior canal BPPV – does not justify the dichotomy be-             limit the need for brain imaging to cases not converted into
tween the inversion of the torsional component, which was          a typical form and not resolved through the usual physical
apogeotropic rather than geotropic, and the persistence of         therapy, but this is achievable only if the knowledge of the
the vertical upbeat component. In fact, the apogeotropic di-       various possible types of posterior canal BPPV is an im-
rection of the torsional component is compatible with an           portant part of the cultural heritage of all otoneurologists.
ampullopetal flow, whereas the upbeat nystagmus is com-
patible with an ampullofugal flow. Another critical point is
                                                                   Acknowledgements
that the intensity of the nystagmus is stronger in its inhibi-
tory phase than in the excitatory one. Both points contrast        We thank Architect Genoveffa Errico for the original illus-
with Ewald’s laws.                                                 trations.
In our series, we observed two similar cases, characterised
by inversion of the torsional phase of the nystagmus for the       References
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