10.14639/0392-100X-N2152
Objective. This study aims to evaluate the utility of the skull-vibration-induced nystagmus test (SVINT) in the selection of patients with Ménière’s disease (MD) for intratympanic injection of gentamicin. To date the indications for this treatment have been based only on subjective elements. Methods. A retrospective study was performed in 20 patients diagnosed with unilateral MD. SVINT were performed monthly and the evoked responses were evaluated. After 6 months, the results from patients who were candidates for gentamicin treatment (G group) were compared with those who did not need it (nG group). Correlation with Dizziness Handicap Inventory (DHI) score was evaluated. Results. 120 tests were performed. Positive SVINTs were identified in 52 cases (43.3%) and included excitatory nystagmus in 18 (34.7%), inhibitory nystagmus in 28 (53.8%), and atypical pattern in 6 cases (11.5%). A significant increase excitatory nystagmus was recorded in group G (p = 0.00001). Moreover, there was a significant increase in the DHI score in group G compared with the nG group (p &lt; 0.0001) and in patients with evoked excitatory nystagmus. Conclusions. The finding of excitatory nystagmus during SVINTs performed on several occasions in the follow-up prior to intratympanic injection of gentamicin strengthens this therapeutic choice.
text/xml
1827-675X
2152
en
Mario Faralli
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
intratympanic gentamicin injection
Skull-vibration-induced nystagmus test in patients who are candidates for intratympanic gentamicin injection
Text.Serial.Journal
https://www.actaitalica.it/
43
Vestibology
2023-04-26
2022-05-11
2023-04-27
2023-04-27
140-148
1
Mario Faralli
2023/04/26
10.14639/0392-100X-N2152
140
Department of Medicine and Surgery, Otorhinolaryngology Section, University of Perugia, Perugia, Italy
1827-675X
intratympanic gentamicin injection
en
148
Skull-vibration-induced nystagmus test in patients who are candidates for intratympanic gentamicin injection
https://www.actaitalica.it/article/download/2152/964
43
ACTA OTORHINOLARYNGOLOGICA ITALICA 2023;43:140-148; doi: 10.14639/0392-100X-N2152




Vestibology


Skull-vibration-induced nystagmus test in patients
who are candidates for intratympanic gentamicin
injection
Skull-vibration-induced nystagmus test in pazienti candidati a gentamicina intratimpanica
Giacomo Ciacca1, Alfredo Di Giovanni1, Luigi Califano2, Vito Enrico Pettorossi3, Giampietro Ricci1, Chiara Pelliccia3,
Mario Faralli1
1
 Department of Medicine and Surgery, Otorhinolaryngology Section, University of Perugia, Perugia, Italy; 2 Department of Audiology
and Phoniatrics, San Pio Hospital, Benevento, Italy; 3 Department of Medicine and Surgery, Human Physiology and Biochemistry
Section, University of Perugia, Perugia, Italy


SUMMARY
Objective. This study aims to evaluate the utility of the skull-vibration-induced nystagmus
test (SVINT) in the selection of patients with Ménière’s disease (MD) for intratympanic
injection of gentamicin. To date the indications for this treatment have been based only on
subjective elements.
Methods. A retrospective study was performed in 20 patients diagnosed with unilateral
MD. SVINT were performed monthly and the evoked responses were evaluated. After 6
months, the results from patients who were candidates for gentamicin treatment (G group)
were compared with those who did not need it (nG group). Correlation with Dizziness
Handicap Inventory (DHI) score was evaluated.
Results. 120 tests were performed. Positive SVINTs were identified in 52 cases (43.3%) and
included excitatory nystagmus in 18 (34.7%), inhibitory nystagmus in 28 (53.8%), and atypi-
cal pattern in 6 cases (11.5%). A significant increase excitatory nystagmus was recorded in
group G (p = 0.00001). Moreover, there was a significant increase in the DHI score in group G
compared with the nG group (p < 0.0001) and in patients with evoked excitatory nystagmus.
Conclusions. The finding of excitatory nystagmus during SVINTs performed on several                 Received: May 16, 2022
occasions in the follow-up prior to intratympanic injection of gentamicin strengthens this          Accepted: November 15, 2022
therapeutic choice.
                                                                                                    Correspondence
KEY WORDS: nystagmus, vestibular system, Ménière’s disease, skull-vibration-induced
                                                                                                    Giacomo Ciacca
nystagmus test, intratympanic gentamicin injection                                                  Department of Medicine and Surgery, Otorhinola-
                                                                                                    ryngology Section, University of Perugia, piazzale
RIASSUNTO                                                                                           Giorgio Menghini 1, 06129 Perugia, Italy
Obiettivi. Questo studio si prefigge di valutare l’utilità dello skull-vibration-induced            E-mail: ciacca.giacomo@gmail.com
nystagmus test (SVINT) nel selezionare, tra i pazienti affetti da malattia di Ménière (MD),
quelli candidabili a iniezione intratimpanica di gentamicina. A oggi l’indicazione a questo           How to cite this article: Ciacca G, Di Giovanni
trattamento si basa su criteri soggettivi.                                                            A, Califano L, et al. Skull-vibration-induced
Metodi. È stato eseguito uno studio retrospettivo in 20 pazienti con una prima diagnosi di MD         nystagmus test in patients who are candidates
unilaterale valutando le risposte oculomotorie evocate allo SVINT eseguito durante i controlli        for intratympanic gentamicin injection. Acta
mensili. Dopo 6 mesi sono state confrontate le risposte ottenute nei pazienti che sono stati can-     Otorhinolaryngol Ital 2023;43:140-148. https://
                                                                                                      doi.org/10.14639/0392-100X-N2152
didati a trattamento con gentamicina (G group) rispetto a quelle ottenute nei pazienti non can-
didati (nG group) indagando inoltre la correlazione con il Dizziness Handicap Inventory (DHI).
                                                                                                    © Società Italiana di Otorinolaringoiatria
Risultati. Il test è risultato positivo in 52 casi su 120 (43,3%) con nistagmo evocato di tipo      e Chirurgia Cervico-Facciale
eccitatorio in 18 (34,7%), inibitorio in 28 (53,8%) e atipico in 6 casi. La frequenza del
pattern eccitatorio è risultata maggiore nel G group rispetto al nG group (p = 0,00001),
                                                                                                                   OPEN ACCESS
inoltre questo pattern correlava con un punteggio DHI maggiore.
Conclusioni. La presenza, in più occasioni, di un nistagmo eccitatorio allo SVINT può               This is an open access article distributed in accordance with
                                                                                                    the CC-BY-NC-ND (Creative Commons Attribution-Non-
essere un criterio oggettivo a sostegno della scelta di trattare il paziente mediante iniezioni     Commercial-NoDerivatives 4.0 International) license. The
intratimpaniche di gentamicina.                                                                     article can be used by giving appropriate credit and mentio-
                                                                                                    ning the license, but only for non-commercial purposes and
PAROLE CHIAVE: nistagmo, sistema vestibolare, malattia di Ménière, skull-vibration-                 only in the original version. For further information: https://
induced nystagmus test, gentamicina intratimpanica                                                  creativecommons.org/licenses/by-nc-nd/4.0/deed.en




140
                                                    SVINT role in selection of patients with Ménière’s disease for intratympanic gentamicin injection




Introduction                                                            requires a short time for execution. For this reason, it can be
                                                                        used in the follow-up of patients undergoing intratympanic
Ménière’s disease (MD) is an inner ear disorder character-              gentamicin treatment where it is desirable to evaluate the
ised by episodes of spontaneous vertigo usually associated              extent of vestibular deafferentation. Conversely, the indica-
with unilateral fluctuating sensorineural hearing loss, tin-            tion for treatment with gentamicin in cases with poor ther-
nitus and aural fullness.                                               apeutic control of the disease is based exclusively on the
Cochlear symptoms can also occur between vertigo epi-                   symptoms reported by the patient. In fact, vestibular tests
sodes. The prevalence of MD is approximately 34-190                     predicting the candidates for this treatment have not been
per 100,000 1-3. The onset of symptoms ranges from the                  described in the literature. From the previously mentioned
third to the seventh decade of life with a slight female pre-           features, SVINT could, in theory, demonstrate its utility.
dominance. The aetiology of the disorder is not fully un-               The aim of this study was to establish a possible correla-
derstood, but increased endolymphatic volume (hydrops)                  tion between the oculomotor patterns evoked during SVINT,
is the commonly accepted pathophysiological mechanism.                  performed on several occasions during follow-up, and the
This finding is also supported by recently developed imag-              degree of disability reported by patients. Consequently,
ing techniques 4,5. MD is associated with various comor-                we wished to verify the usefulness of the test in selecting
bidities such as autoimmune disorders 6 and migraine 7. In              patients for treatment with intratympanic injection of gen-
2015, the Barany Society proposed the following diagnos-                tamicin. In this case, the hypothesis of an excitatory response
tic criteria for definite MD 8:                                         as an expression of a recurrent or persistent functional condi-
• two or more spontaneous episodes of vertigo each last-                tion, as opposed to deafferentation, could represent a condi-
    ing 20 minutes to 12 hours;                                         tion resulting in vertigo episodes and the patient’s disability.
• audiometrically documented low to medium frequency
    sensorineural hearing loss in one ear, defining the affect-
    ed ear, on at least one occasion before, during, or after           Materials and methods
    one of the episodes of vertigo;                                     A retrospective study was conducted on a population of 20
• fluctuating aural symptoms (hearing, tinnitus or full-                consecutive patients experiencing unilateral MD diagnosed
    ness) in the affected ear;                                          in the period from January 30, 2016 to March 6, 2021. All
• not better accounted for by another vestibular diagnosis.             patients met diagnostic criteria for definite MD according
Vestibular evaluation does not offer any contribution to                to the Barany Society 8. Patients who followed a personal
the diagnosis of the disease. Indeed, in the period between             protocol for monitoring the disease and accepting the thera-
episodes, there are often no changes in the results of con-             peutic option were included in the study. This protocol in-
ventional tests. In the more advanced stages of the disease,            cluded monthly clinical tests for 6 months after diagnosis
it is more likely to find hypofunctional aspects as an ex-              of the disease. All patients underwent the same therapy
pression of a progressive sensorineural deterioration on the            during the entire period and were invited to write a diary
vestibular side, similar to what occurs for cochlear func-              detailing the vertigo episodes that occurred. On the occa-
tion. Spontaneous nystagmus can be observed during epi-                 sion of each monthly control, in addition to a global au-
sodes and the related vestibular tests give rise to responses           diological and vestibular evaluation, including caloric and
that express a paretic (deficit) or irritative functional state.        video-Head Impulse test (vHIT), SVINTs were performed.
However, it is often possible to record opposing responses              At the end of the follow-up, the Dizziness Handicap Inven-
that express a functional dissociation in both the frequency            tory (DHI) was administered to each patient for subjective
(caloric vs video Head Impulse Test) and topographical do-              assessment of the degree of disability 14. Finally, patients
main (macular vs canal clinical signs) 9,10.                            were asked whether the therapeutic measures adopted were
The skull-vibration-induced nystagmus test (SVINT) is                   considered to be satisfactory. In those dissatisfied with clin-
one of the methods recently introduced in clinical practice             ical control, treatment with intratympanic gentamicin was
for the study of vestibular function 11. In a recent analysis, it       considered as an alternative treatment. In these patients, the
was the most sensitive vestibular test, provoking a consist-            treatment was reserved for those with sensorineural hearing
ent nystagmus beating on the healthy side in 58.7% of a                 loss with pure-tone audiometry > 50 dB and serviceable
large population of MD patients 12. Intratympanic injection             hearing in the contralateral ear. Vestibular impairment on
of gentamicin is widely used in the treatment of disabling              the unaffected side was excluded by a complete vestibular
unilateral MD. In this case, a profound vestibular deaffer-             evaluation. The results that emerged from each test, at the
entation is required to obtain subjective improvement dur-              planned control visits, were entered into a database from
ing treatment. A multifrequency vestibular study for this               which the data were extracted for statistical evaluation.
evaluation includes SVINT, head shaking test (HST) and                  Patients with clear migraine comorbidity were excluded
caloric test 13. SVINT, in particular, is easy to apply and             from the study, and received a different medical therapy.



                                                                                                                                               141
G. Ciacca et al.




A brain imaging study (MRI with or without gadolinium,          Results
angio MRI) was performed in all patients to exclude acous-
tic schwannoma or neurovascular conflicts and a high-res-       Of the 23 patients initially enrolled after diagnosis of MD,
                                                                three dropped out of follow-up. Of these, two presented
olution CT of the petrous bone for interruptions of the otic
                                                                with recurrent paroxysmal positional vertigo which re-
capsule. SVINT was performed at a frequency of 100 Hz
                                                                quired a different treatment and one patient was affected by
with an oscillation amplitude of 0.8 mm for each cycle. The
                                                                COVID-19. The remaining 20 patients were considered eli-
vibrator was applied and held firmly perpendicular to the
                                                                gible for the study as they completed the series of tests pro-
skin above the mastoid process, posterior to the auricle, at
                                                                vided and followed the proposed therapeutic indications.
the level of the external acoustic meatus. Three stimula-
                                                                In 8 patients (group G), the results after intratympanic in-
tions were performed on each mastoid lasting 5-10 seconds
                                                                jection of gentamicin were taken into consideration as the
each 15. Eye movements were studied with Frenzel video
                                                                results obtained from therapy were inconsistent. Treatment
glasses and visual fixation of both eyes was denied. The test
                                                                with gentamicin was proposed in six of these patients as
was considered positive when the same type of nystagmus
                                                                they had unilateral hearing loss and a normal contralateral
was evoked in all six tests. According to the evoked ocu-
                                                                vestibular function. All accepted the therapeutic measure.
lomotor response, the following patterns were considered:
                                                                On the other hand, the results from 12 patients were satis-
• normal pattern: no nystagmus evoked during SVINT;             factory and they did not require treatment with gentamicin
• pathological pattern: nystagmus evoked during SVINT.          (group nG).
As part of the pathological pattern, the following have been    A total of 120 SVINTs were performed monthly for 6
identified:                                                     months in the 20 patients recruited for this study (20 pa-
• inhibitory type: evoked nystagmus (purely or mainly           tients undergoing 6 monthly tests). A normal pattern
   horizontal) beating towards the unaffected (healthy)         emerged in 68 (56.7%) cases and a pathological response
   side;                                                        in 52 (43.3%), including 28 Inhibitory type, 18 Excitatory
• excitatory type: evoked nystagmus (purely or mainly           type and 6 Atypical type (Tab. I). The correlation between
   horizontal) beating towards the affected side;               SVINT and the results of caloric and vHIT are shown in
• atypical type: evoked nystagmus (not purely or mainly         Figures 1 and 2. The incidences of subtypes within the path-
   horizontal) with clear vertical and/or torsional compo-      ological oculomotor response were 53.8, 34.7 and 11.5%,
   nents.                                                       respectively, for the Inhibitory, Excitatory and Atypical
The global incidence of normal and pathological patterns        types. Among the 48 SVINTs performed in the 8 patients in
(Inhibitory, Excitatory and Atypical) was calculated in all     group G, a normal pattern was recorded in 20 cases (41.7%)
patients who completed the protocol. A comparative as-          and a pathological pattern in 28 (58.3%), of which there
sessment was made between the group of patients who             were 6 of the Inhibitory type (6/48:12.5%), 16 Excitatory
were candidates for treatment with intratympanic injection      type (16/48: 33.3%) and 6 Atypical (6/48: 12.5%). In the
of gentamicin (group G) and the group of patients not can-      72 SVINTs performed in the 12 patients in the nG group,
didates for this treatment (group nG). At the same time, the    a normal pattern was identified in 48 (66.7%) controls and
DHI scores that emerged in the two groups (G vs nG) were        a pathological pattern in 24 (33.3%), of which 22 were of
compared. Furthermore, the DHI scores and the number of         the Inhibitory type (22/72: 30.5%), 2 Excitatory type (2/72:
vertigo episodes were compared between the group of pa-         2.8%) and none of the Atypical type. A significant increase
tients with at least one pathological pattern of excitatory     (p = 0.00678) in the pathological oculomotor pattern (chi-
type (Exc group), which emerged in at least one of the tests    squared test) was therefore observed in the G group. Com-
performed, and those who never presented this type during       parison between oculomotor patterns in group G showed a
the protocol (nExc group). At each control, cases were con-     significant increase in the Excitatory type compared to that
sidered in whom at least one vertigo episode was reported       of the Inhibitory type (p = 0.00001). On the other hand, in
within the previous 3 days, or within the following 3 days,     patients belonging to the nG group, the oculomotor pattern
or within the previous and the following 3 days. In this way,   of Inhibitory type appeared to be significantly increased
the correlation of these cases with the oculomotor pattern      compared to that of Excitatory type (p = 0.0001). Over the
evoked at SVINT was assessed. The statistical evaluation        follow-up period, the mean number of vertigo attacks in
compared the percentages of the parameter under examina-        the Exc group was 15.6 ± 9.90, which was significantly
tion between groups using the chi-squared test. Compari-        higher (p = 0.0019) than in the nExc group (4.17 ± 2.69)
son of means (M) and standard deviations (SD) of the DHI        (Tab. II). At 39 controls (32.5%), patients reported at least
and the vertigo episodes were made using a t-test. The level    one vertigo episode within 3 days, before and/or after the
for a statistically significant difference between groups was   control itself. In particular, vertigo occurred in the 3 pre-
taken as p < 0.05.                                              vious days in 20 cases and in the 3 following days in 10



142
                                                                     SVINT role in selection of patients with Ménière’s disease for intratympanic gentamicin injection




Table I. Oculomotor patterns evoked in each of 20 patients in monthly clinical SVINTs for 6 months after diagnosis of Ménière’s disease.
 SVINT (month)
 Patient                  1°                       2°                       3°                       4°                       5°                       6°                  IIG
 1                    Inhibitory                Normal                   Normal                  Inhibitory                Normal                   Normal                 No
 2                    Inhibitory                Normal                  Inhibitory                Normal                   Normal                   Normal                 No
 3                     Normal                   Normal                   Normal                   Normal                  Excitatory               Excitatory              Yes
 4                     Normal                   Normal                  Inhibitory               Inhibitory                Normal                   Normal                 No
 5                     Normal                  Inhibitory                Normal                   Normal                  Inhibitory                Normal                 No
 6                     Normal                  Inhibitory               Inhibitory                Normal                   Normal                   Normal                 No
 7                    Excitatory               Inhibitory                Normal                   Normal                   Atypical                Excitatory              Yes
 8                    Inhibitory               Excitatory                Normal                   Normal                   Atypical                Excitatory              Yes
 9                    Inhibitory               Excitatory                Normal                  Inhibitory                Normal                   Normal                 No
 10                    Normal                   Normal                   Atypical                Excitatory                Normal                  Excitatory              Yes
 11                    Normal                  Inhibitory                Normal                   Normal                   Normal                  Inhibitory              No
 12                    Normal                   Normal                   Normal                   Normal                   Normal                  Inhibitory              No
 13                    Normal                  Inhibitory                Normal                   Normal                  Inhibitory                Normal                 No
 14                   Inhibitory                Normal                   Normal                   Normal                  Excitatory               Excitatory              Yes
 15                    Normal                   Normal                   Normal                  Inhibitory                Normal                  Inhibitory              No
 16                   Excitatory                Normal                   Normal                   Normal                  Excitatory                Atypical               Yes
 17                   Excitatory               Inhibitory               Inhibitory                Normal                   Normal                   Normal                 No
 18                   Inhibitory               Excitatory                Normal                   Normal                   Atypical                Excitatory              Yes
 19                    Normal                   Normal                  Excitatory                Atypical                Excitatory               Inhibitory              Yes
 20                   Inhibitory                Normal                  Inhibitory                Normal                   Normal                   Normal                 No
SVINT: skull-vibration-induced nystagmus test; IIG: intratympanic injection of gentamicin; Yes: Patients who were candidates for gentamicin injection; No: Patients who were not con-
sidered to be candidates for gentamicin injection.




Figure 1. Pathological response to SVINT, caloric and vHIT. The distribution of the pathological responses among the 20 recruited patients is illustrated on the
abscissa. The ordinate illustrates the number of pathological responses to vestibular tests at the six controls performed by each patient.


cases. In the remaining 9 cases, at least one vertigo episode                                at the control. A positive SVINT emerged in 29 (74.3%)
was recorded in both the previous and the following 3 days                                   of these 39 controls, of Inhibitory, Excitatory and Atypi-



                                                                                                                                                                              143
G. Ciacca et al.




Figure 2. Distribution of the oculomotor patterns within patients with pathological responses to SVINT (52), caloric (22) and vHIT (14) during the six controls
performed by each patient. As part of the pathological responses that emerged from the caloric test, only an Inhibitory type pattern was recorded (hypo-reflective
affected side). Conversely, an Excitatory pattern (VOR gain > 1) also emerges in the pathological responses to vHIT (hyperreflective affected side). Atypical nys-
tagmus evoked is an exclusive SVINT response.



cal type in 11, 12 and 6 cases, respectively. In the 11 cases                      Discussion
of Inhibitory type, vertigo episodes always occurred in the
                                                                                   Intratympanic injection of gentamicin is one of the treat-
3 days preceding the control and never in the following 3
                                                                                   ments commonly used in unilateral disabling MD. Intracta-
days (Tab. III). Statistical evaluation showed a significant
                                                                                   ble MD is defined when patients have more than one severe
increase in the incidence of positive SVINTs in the series
                                                                                   vertiginous episode per month with repetitive episodes for
of 39 controls performed closer to the vertigo episode com-
                                                                                   more than 6 months, despite conservative medical manage-
pared to those in which vertigo occurred outside the time
                                                                                   ment 16. On this basis, the temporal criterion adopted by
range considered (p < 0.00001). In particular, in the series
                                                                                   us in the follow-up of MD patients appears to be justified.
of controls closer to the vertigo episode, there was a signifi-                    Several studies highlight the favourable results obtained
cant increase in the incidence of Excitatory (p = 0.00078)                         following treatment with different types of local applica-
and Atypical (p = 0.00195) types compared to the series of                         tion, related to therapeutic control of the disease and pres-
controls in which vertigo occurred outside the considered                          ervation of hearing threshold 13,17-19. To date, the indication
time range. On the other hand, no significant difference                           for this treatment is based on subjective elements, in the
emerged between the incidence values of the Inhibitory                             absence of clinical markers resulting from conventional
type between the series of controls performed closer to the                        vestibular tests applied in clinical practice. However, com-
vertigo episode compared to the series in which vertigo oc-                        plete bilateral objective evaluation of vestibular function is
curred outside the considered time range (p = 0.7666). The                         always required, especially in the elderly, prior to admin-
overall mean DHI score in the patients enrolled in the study                       istering intratympanic gentamicin. This in order to avoid
was 41.8 ± 9.2 (55.5 ± 7.66 in the G group and 32.66 ± 7.58                        the possible outcome in bilateral vestibulopathy when the
in the nG group). A mean DHI score of 51.8 ± 8.7 was                               opposite side is hypo-reflective.
recorded in patients who presented at least one Excitatory                         On the other hand, SVINT is a useful tool to evaluate the
type response on one or more of the SVINTs performed.                              severity of the deafferentation after intratympanic gen-
The score was 29.2 ± 9.3 in the group of patients who never                        tamicin application. A preferential action, with a relative
presented Excitatory type responses on SVINT. Therefore,                           vestibulotoxic effect, has been demonstrated for gen-
there was a significant increase (p < 0.0001) in the DHI                           tamicin on irregular sensory cells of type I, which are more
score in group G (group G vs group nG) and in the Exc                              sensitive to high frequency vibratory stimuli 20. After one
group (Exc group vs nExc group).                                                   injection, Junet et al. observed a positive SVINT beating



144
                                                                        SVINT role in selection of patients with Ménière’s disease for intratympanic gentamicin injection




Table II. Number of vertigo episodes reported by the patient during the observation period and related to the groups examined. On the occasion of each control,
the pattern evoked at SVINT and the number of episodes occurring in the previous month are indicated.
 SVINT (mount)
 Patient              1°                    2°                     3°                     4°                    5°                  6° test            Group           Total crisis/
                                                                                                                                                     Exc-nExc/             IGG
                                                                                                                                                       G-nG            considered
 1                 5/(Inh)                3/(Nor)               3/(Nor)                0/(Inh)                1/(Nor)               0/(Nor)            nExc/nG            12 (No)
 2                 4/(Inh)                2/(Nor)               2/(Inh)                0/(Nor)                0/(Nor)               0/(Nor)            nExc/nG             8 (No)
 3                 4/(Nor)                2/(Nor)               2/(Nor)                1/(Nor)                4/(Exc)               3/(Exc)             Exc/G             16 (Yes)
 4                 2/(Nor)                1/(Nor)               3/(Inh)                1/(Inh)                1/(Nor)               0/(Nor)            nExc/nG             8 (No)
 5                 5/(Nor)                4/(Inh)               2/(Nor)                1/(Nor)                1/(Inh)               1/(Nor)            nExc/nG            14 (No)
 6                 4/(Nor)                4/(Inh)               1/(Inh)                0/(Nor)                0/(Nor)               1/(Nor)            nExc/nG            10 (No)
 7                 3/(Exc)                1/(Inh)               3/(Nor)                2/(Nor)                4/(Aty)               3/(Exc)             Exc/G             16 (Yes)
 8                 4/(Inh)                4/(Exc)               3/(Nor)                2/(Nor)                2/(Aty)               5/(Exc)             Exc/G             19 (Yes)
 9                 3/(Inh)                2/(Exc)               2/(Nor)                1/(Inh)                0/(Nor)               0/(Nor)             Exc/nG             8 (No)
 10                2/(Nor)                1/(Nor)               2/(Aty)                3/(Exc)                2/(Nor)               3/(Exc)              Exc/G            13 (Yes)
 11                3/(Nor)                1/(Inh)               3/(Nor)                0/(Nor)                1/(Nor)               0/(Inh)            nExc/nG             8 (No)
 12                5/(Nor)                2/(Nor)               1/(Nor)                0 (Nor)                1/(Nor)               0/(Inh)            nExc/nG             9 (No)
 13                3/(Nor)                2/(Inh)               3/(Nor)                1/(Nor)                0/(Inh)               1/(Nor)            nExc/nG            10 (No)
 14                2/(Inh)                3/(Nor)               2/(Nor)                2 /(Nor)               4/(Exc)               3/(Exc)              Exc/G            16 (Yes)
 15                4/(Nor)                5/(Nor)               2/(Nor)                1/(Inh)                1/(Nor)               1/(Inh)            nExc/nG            14 (No)
 16                6/(Exc)                4/(Nor)               3/(Nor)                3/(Nor)                4/(Exc)               3/(Aty)              Exc/G            23 (Yes)
 17                5/(Exc)                3/(Inh)               3/(Inh)                0/(Nor)                0/(Nor)               0/(Nor)             Exc/nG            11 (No)
 18                3/(Inh)                3/(Exc)               2/(Nor)                2/(Nor)                3/(Aty)               4/(Exc)              Exc/G            17 (Yes)
 19                2/(Nor)                1/(Nor)               4/(Exc)                2/(Aty)                4/(Exc)               4/(Inh)              Exc/G            17 (Yes)
 20                2/(Inh)                1/(Nor)               1/(Inh)                2/(Nor)                0/(Nor)               0/(Nor)            nExc/nG             6 (No)
Nor: normal type; Inh: inhibitory type; Exc: excitatory type; nExc: not excitatory type; Aty: atypical; G: gentamicin group; nG: no gentamicin group; SVINT: skull-vibration-induced nys-
tagmus test.



toward the unaffected side in 75% of patients treated for                                      Caloric tests in patients suffering from MD generally shows
disabling MD. After 7 injections, the same authors reported                                    impairment of the affected side in presence of a normal or
the same results in all of the patients examined 13. SVINT                                     slightly increased VOR. A recent paper attributed this to
represents a method that is easy to perform, rapid, inex-                                      the hydropic enlargement of the membranous labyrinth 24.
pensive, of unequivocal interpretation and above all, unlike                                   It is possible that the physical modification induced by hy-
the caloric test, well tolerated. As reported in the literature,                               drops could make the vestibule more sensitive to vibratory
SVINT is the most sensitive test to detect an imbalance in                                     stimulus and less responsive to caloric ones. This may ex-
the vestibular system during the intercritical period outside                                  plain the dissociation between calorics and SVINT and the
vertigo episodes 12. Our data are consistent with those re-                                    presence of the excitatory pattern. However, as SVINT is
ported in the literature.                                                                      the only test that evaluates the higher frequencies, it cannot
In a recent paper, SVINT was seen to be more sensitive                                         be excluded that excitatory pattern is the sign of a selec-
compared to vHIT, provoking a consistent nystagmus beat-                                       tive suffering of vestibular receptors. In the present work,
ing toward the unaffected side in 301 of 511 patients re-                                      the presence of this pattern seems to be associated with the
cruited (58.7%), apart from two cases in whom the nystag-                                      crisis as sign of an altered state of the labyrinth. This is con-
mus direction was toward the hydropic side 12. Hong et al.                                     sistent with the studies of Lee et al. that reported a higher
analysed 52 MD and observed a positive SVINT in 71% of                                         percentage of excitatory pattern when the tests were per-
patients; in many cases (27%), the evoked nystagmus was                                        formed close to a crisis 25, while Teggi et al., who evaluated
beating toward the lesion side 21. Dumas et al. described a                                    patients only during a vertigo free period, described nystag-
positive SVINT in 71% of patients with MD, mostly ob-                                          mus beating towards the affected side only in 1% of cases.
served in a period closer to the vertigo episode 22. Those au-                                 For these reasons, SVINT can be considered a simple aid to
thors also reported an excitatory nystagmus in 15.8% and a                                     monitor vestibular function in patients suffering from MD
frequent discordance with caloric and head shaking test 23.                                    and provide valid feedback on the response to therapy, even



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Table III. Vertigo episodes occurring within 3 days of the planned control (-3: 3 days before, +3: 3 days after, ± 3 days before and after). >±3: vertigo episodes
occurred outside the time range considered. The pattern evoked at SVINT on the occasion of each control is indicated.
 SVINT (mount)
 Patient                                  1°                       2°                        3°                  4°              5°                6° test
 1                                    -3 (Inh)                 >±3 (Nor)                  -3 (Nor)            >±3 (Inh)       >±3 (Nor)          >±3 (Nor)
 2                                    -3 (Inh)                 >±3 (Nor)                  -3 (Inh)            >±3 (Nor)       >±3 (Nor)          >±3 (Nor)
 3                                    -3 (Nor)                 >±3 (Nor)                 >±3 (Nor)            >±3 (Nor)       +3 (Exc)            -3 (Exc)
 4                                   >±3 (Nor)                 >±3 (Nor)                  -3 (Inh)            >±3 (Inh)       >±3 (Nor)          >±3 (Nor)
 5                                   ±3 (Nor)                   -3 (Inh)                 >±3 (Nor)            >±3 (Nor)       >±3 (Inh)          >±3 (Nor)
 6                                   +3 (Nor)                   -3 (Inh)                 >±3 (Inh)            >±3 (Nor)       >±3 (Nor)          >±3 (Nor)
 7                                   +3 (Exc)                  >±3 (Inh)                  -3 (Nor)            >±3 (Nor)       ±3 (Aty)           >±3 (Exc)
 8                                    -3 (Inh)                 ±3 (Exc)                  >±3 (Nor)            >±3 (Nor)       ±3 (Aty)            -3 (Exc)
 9                                   >±3 (Inh)                 >±3 (Exc)                 >±3 (Nor)            >±3 (Inh)       >±3 (Nor)          >±3 (Nor)
 10                                  >±3 (Nor)                 >±3 (Nor)                 +3 (Aty)             +3 (Exc)        >±3 (Nor)          >±3 (Exc)
 11                                  >±3 (Nor)                 >±3 (Inh)                  -3 (Nor)            >±3 (Nor)       >±3 (Nor)          >±3 (Inh)
 12                                   -3 (Nor)                 >±3 (Nor)                 >±3 (Nor)            >±3 (Nor)       >±3 (Nor)          >±3 (Inh)
 13                                  >±3 (Nor)                  -3 (Inh)                 >±3 (Nor)            >±3 (Nor)       >±3 (Par)          >±3 (Nor)
 14                                  >±3 (Inh)                 >±3 (Nor)                 >±3 (Nor)            >±3 (Nor)       ±3 (Exc)           >±3 (Exc)
 15                                   -3 (Nor)                 ±3 (Nor)                  >±3 (Nor)            >±3 (Inh)       >±3 (Nor)          >±3 (Inh)
 16                                  ±3 (Exc)                  >±3 (Nor)                 >±3 (Nor)            >±3 (Nor)       +3 (Exc)            -3 (Aty)
 17                                  ±3 (Exc)                   -3 (Inh)                  -3 (Inh)            >±3 (Nor)       >±3 (Nor)          >±3 (Nor)
 18                                  >±3 (Inh)                 >±3 (Exc)                 +3 (Nor)             >±3 (Nor)       +3 (Aty)           >±3 (Exc)
 19                                  >±3 (Nor)                 >±3 (Nor)                 ±3 (Exc)             +3 (Aty)        +3 (Exc)            -3 (Inh)
 20                                  >±3 (Inh)                 >±3 (Nor)                 >±3 (Inh)            >±3 (Nor)       >±3 (Nor)          >±3 (Nor)
Nor: normal type; Inh: inhibitory type; Exc: excitatory type; Aty: atypical type.
Bold type indicates vertigo episodes occurring within 3 days (before and /or after) of the planned control.



if it must always be integrated with a complete bilateral                                      oculomotor patterns in which treatment with intratympanic
vestibular evaluation.                                                                         gentamicin was not considered necessary would seem to
The aim of this study was to examine the usefulness of the                                     indicate a quiescent functional state favourable to the clini-
SVINT in providing objective data that can support the                                         cal course and, in general, there is a good response to the
decision to administer intratympanic gentamicin based on                                       therapeutic measures adopted. The hypothesis of a hyper-
anamnestic elements in those cases not responsive to medi-                                     functional state responsible for the symptoms of MD is
cal therapy. The main finding of our study is represented                                      also confirmed by DHI, which reveals a greater degree of
by the higher incidence of vestibular alterations, identified                                  subjective disability in these patients. The final dataset con-
by the SVINT during controls, in patients with MD who,                                         sidered in this study is related to the occurrence of atypical
at the end of the follow-up, needed intratympanic gen-                                         patterns induced by the SVINT and which, although not
tamicin injection. In particular, excitatory-type responses                                    frequent, require some speculative interpretation. The pres-
are more frequently expressed in these patients. In the irri-                                  ence of torsional and/or vertical components that replace or
tative phase, the disease may enhance the response of affer-                                   increase the horizontal component of the nystagmus, and
ent neurons 26 which causes an imbalance in neural activity                                    which are more frequently identifiable, could be explained
between the two vestibular nuclei and thus results in nys-                                     by a greater involvement of the endolymphatic hydrops in
tagmus beating toward the affected side 27. The finding of a                                   the posterior labyrinth with involvement of more ampullary
hyperfunctional state that persists even outside the episode                                   and/or macular receptors. In all six cases recorded in our
could represent a trigger for new episodes and, at the same                                    study, occurrence of this pattern during SVINTs carried out
time, favour a condition of chronic dizziness. In fact, this                                   in close temporal relationship with vertigo episodes makes
study shows that the finding of an excitatory pattern, dur-                                    this hypothesis more credible. The constant association
ing the pre-established controls, significantly increases the                                  with excitatory-type responses in the same patient, evoked
possibility of an imminent crisis in subsequent days. On the                                   during SVINTs performed at different times, seems to im-
other hand, the finding of a higher incidence of deficient                                     part an unfavourable prognostic significance for the Atypi-



146
                                                  SVINT role in selection of patients with Ménière’s disease for intratympanic gentamicin injection




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