Discussion
Although SCC channel VOR gain values were shown in BPPV patients in the
study, demonstrating that SCC VOR gain values returned to normal after
medical treatment or canalith repositioning procedures could increase
the validity of this study for BPPV. In addition, vHIT protocol
performed after making a definite diagnosis with an examination and
medical history. Also, the clinician performing the vHIT test was a
member of the clinician group conducting the study protocol so this
increases the risk of bias since of unfavorable blindness.
The most common cause of vertigo is BPPV and is mostly caused by
posterior SCC in this study and as the literature indicates [1].
Although 40% of BPPV rates originating from lateral SCC have recently
been mentioned, this rate is around 20% in studies with a large number
of participants and there is no prevalence study in recent literature
[9, 10]. In some studies, the variability of these rates has been
attributed to the missed diagnosis of LSCC-induced BPPV due to the high
spontaneous recovery rates [11-13]. Clinically in this study, BPPV
was most commonly caused by posterior SCCs (PSCCs) (n=49, 66.2%), and
LSCCs involvement were detected in 20 (27.2%) patients. Pathological
VOR gain values are detected in 20 (27%) patients for PSCC and in 36
(48.6%) patients for LSCCs. The clinical findings in our study are
compatible with the literature, but according to the vHIT test results,
LSCCs participation is higher than the rates mentioned in the
literature.
Mahringer et al. [6]. found the sensitivity and specificity as 93%
and 72% in acute cases (n = 49, onset <5 days), 59% and 93%
in other cases (n= 123) for vHIT compared to clinical diagnosis. A total
of 42 (34%) patients with BPPV were included in this study, and vHIT
was found to be positive in 25.7% of BPPV patients in the acute phase.
The sensitivity and specificity for BPPV were not calculated separately
[6]. Guan et al. [14] reported that VOR gain values were
statistically significantly lower in the acute vertigo group (n= 96,
onset <7 days), which included 43 BPPV patients, compared to
normal participants (n=50). In this study, VOR gain values were found to
be significantly lower in the VN group compared to the acute vertigo
group. The sensitivity and specificity for BPPV were not calculated in
this study. Additionally, for VN, sensitivity and specificity were
reported as 87.9% and 94.8% among all patients [14]. In this study
sensitivity and specificity found to be 55.4% and 81.2% for all BPPV
patients. The results are lower than the rates reported in other
peripheral vestibular diseases in the literature. Recent literature does
not recommend vHIT testing for the diagnosis of BPPV patients, so there
are no detailed results specific to BPPV patients and comparative
analysis is difficult [5, 7]. The highest sensitivity rate was found
for LA and RA SCC (100%), while the highest specificity was calculated
for RL SCC (22.5%). However, the reliability of these results is low
due to the small number of cases for each SCC.
Blödow et al. [15] detected average VOR gain value as 0,96±0,08 on
the right and 0.97± 0,.09 on the left in VHIT. They accepted the VOR
gain below 0,79 as pathological for LSCC. The average VOR gain of
pathological LSCC was detected by 0.44± 0.20 in all patients (n=117).
This value was detected 0.43±0.20 in patients with vestibular neuritis
(52) and 0.60± 0.20 for Meniere’s disease (n= 22) [15]. In our
study, the average VOR gain value was 0,74 ±0,08 in BPPV, 0.65±0.11 in
VN (LSCC), and 0.66±0.05 in MD (p=0.253). Both accepted threshold and
deficient VOR gain for VN and MD similar in analogous studies
[16-18]. Miłoński et al. [19] found the rate of 2 or more SCC
involvement as 17.8% in 73 patients with no final diagnosis. Also,
these findings are consistent with the rates in our study, VOR gain
deficiency was detected in 15 (20.2 %) patients in one or more SCCs in
the BPPV group.
Clinical findings in this study coincide with the literature in patients
with peripheral vertigo, but the vHIT protocol is inconvenient for
differentiating patients with a diagnosis of BPPV or determining the
specific SCC involvement. Korsager et al. [20] reported abnormal
high gain values in vHIT caused by technical error as hand position,
head rotation speed of the operator, tightly or loosely fastened device,
distance from the wall, unsuitable calibration.
The inconvenience of vHIT test in the diagnosis of BPPV may be due to
the reasons listed above, but our final conclusion is parallel with the
literature [21]. VOR gains obtained vHIT protocol does not work for
BPPV. Also, the clinically detected responsible SCC does not accurately
represent by vHIT. In accordance with the literature, vHIT is a fast,
simple, and comfortable test in the differential diagnosis of peripheral
and central vertigo. The diagnostic value of vHIT in VN and DM has been
accepted in the literature. Also, vHIT seems an optimal option for
demonstrating peripheral vertigo in patients complaint of acute vertigo,
and when supported by clinical information and physical examination, can
assist the clinician in the definitive diagnosis.