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.