Serum otolin-1 level is specific to benign paroxysmal positional vertigo
Article information
Abstract
Objectives
When we see patients with a history of positional vertigo (PV), many patients are diagnosed with benign paroxysmal PV (BPPV) by performing a typical history and nystagmus during a positioning maneuver. Recent studies reported that Otolin-1 can be detected in serum and that its levels significantly increase with age and BPPV. Herein, we tried to study the relationship between serum otolin-1 level and the other clinical aspects in patients with PV.
Methods
We measured the serum levels of otolin-1 in 117 BPPV patients (82 females; age range, 43–92 years; mean age±standard deviation [SD], 68.5±10.5 years), referred to as the BPPV group; and nine patients (seven females; age range, 61–79 years; mean age±SD, 66.9±5.9 years) with PV not compatible with BPPV, referred to as another PV group. All the BPPV patients were treated with an appropriate canal repositioning maneuver followed by blood sampling within 1 week.
Results
The serum levels of otolin-1 were higher in the BPPV group than in another PV group (mean±SD, 350.1±319.1 pg/mL vs. 183.6±134.1 pg/mL, respectively; p=0.037). However, there were no differences in both laboratory findings (serum vitamin D, C-telopeptide of type collagen, and bone mineral density) and clinical findings (age, sex, vertigo duration, ear disease, ear symptom, migraine, motion sickness, trauma, and previous BPPV) between these two groups.
Conclusions
Serum otolin-1 level could help predict the current existence of BPPV in patients with PV. However, further validation studies are needed.
INTRODUCTION
Otolin-1, a protein found in the inner ear, plays a crucial role in otolith (“ear stones” of fishes) and otoconia formation (“ear dust” of higher vertebrates), which are essential for balance [1]. The protein’s C1q-like domain, particularly, is important for its stability and function, with calcium ions influencing its structure and stability in this process [1]. This domain is also involved in forming trimers and higher-order complexes necessary for otolith morphogenesis [2]. National mutations in the gC1q domain of otolin-1 can negatively impact its stability and function, potentially leading to balance disorders [3]. Research has consistently shown a significant increase in serum otolin-1 levels in patients with benign paroxysmal positional vertigo (BPPV) compared to healthy controls [4-7]. Otolin-1 has also been found to increase blood levels with age, particularly in individuals over 65 years old [8]. This increase in otolin-1 might have been linked to age-related otoconia degeneration and a higher prevalence of BPPV in older individuals. Therefore, serum otolin-1 levels have been proposed as a potential biomarker for BPPV episodes [4,5]. However, the relationship between otolin-1 and vitamin D, associated with BPPV, is not statistically significant [4]. Before otologic serological biomarkers, such as otolin-1, can be adopted into clinical practice, their characteristics must be defined in various situations. Our study aims to identify serum otolin-1 in BPPV and other positional vertigo and to determine differences in BPPV subtypes. The main focus is to determine whether otolin-1 levels can be used as a marker for differential diagnosis by comparing the otolin-1 levels between two groups with similar clinical symptoms.
METHODS
Ethics Statement
The study was approved by the Institutional Review Board of Chungnam National University Hospital (No. CNUH 2021-07-070). All participants provided written informed consent before participation.
Study Population and Data Collection
This retrospective study utilized data from the dizziness clinic of Chungnam National University Hospital. The serum samples were collected from 2012 to 2021 and are stored in the human bank of the Hospital. These samples come from patients evaluated at the dizziness clinic and neurology department. Out of the total samples, 126 were identified from patients with positional vertigo. This subgroup was selected for further analysis. Most patients (n=117, 92.9%) were diagnosed with BPPV. The other positional vertigo group (n=9) consisted of seven patients who initially presented with positional vertigo but had resolved BPPV with no nystagmus or vertigo at the time of examination, one patient with left vestibulopathy, and one patient with probable Menière’s disease.
Clinical Findings
This includes data such as age, sex, duration of vertigo, any associated ear disease, ear symptoms, history of migraine, motion sickness, trauma, and previous episodes of BPPV.
Laboratory Findings
Assays include serum vitamin D levels, the c-telopeptide of type collagen (CTX; a marker of bone resorption), and bone mineral density measurements.
Measurement of Serum Otolin-1 Levels
The blood samples were stored at –80 ℃ to preserve biological integrity. Serum otolin-1 concentrations were quantified using an enzyme-linked immunosorbent assay. To establish a standard curve, otolin-1 standards were serially diluted to create a range of known concentrations (0, 200, 400, 600, 800, 1,000, and 1,200 pg/mL). Each standard was assayed in triplicate. Absorbance was measured at 450 nm using a spectrophotometer. The standard curve was plotted with the absorbance values on the y-axis against the concentrations on the x-axis. The relationship between otolin-1 concentration and absorbance was determined by linear regression, yielding the equation y=0.0014x–0.0467 with a coefficient of determination (R2) of 0.9931, indicating an excellent linear fit.
Measurement of Serum Vitamin D
Blood sampling was conducted on the day of the patient’s visit with symptoms whenever possible. For BPPV cases, the tests were performed no later than 7 days after the canalith repositioning maneuver. Serum samples were kept at 2 to 8 ℃. If the test was not run within 24 hours, samples were stored at –20 ℃. The serum level of 25-OH vitamin D was measured using 125I-radioimmunoassay based on patented monoclonal antibodies (DIAsource ImmunoAssays).
Statistical Analysis
Statistical analyses included the chi-square tests or Fisher exact tests for dichotomous variables, the Mann-Whitney U-test and the Kruskal-Wallis test for continuous variables to compare the groups. All tests were performed using IBM SPSS Statistics (ver. 26, IBM Corp.), and a p-value of <0.05 was considered significant.
RESULTS
Populations
Our study analyzed a cohort of 126 patients diagnosed with positional vertigo. Most patients (n=117, 92.9%) were diagnosed with BPPV. Among those diagnosed with BPPV, two subtypes were predominant: BPPV of the posterior canal (BPPV-PC) and the horizontal canal (BPPV-HC). Specifically, 74 patients (58.7%) had BPPV-PC, while 41 (32.6%) exhibited BPPV-HC. A smaller number of patients had other types of BPPV, accounting for two cases (1.6%). Further subclassification of the BPPV-HC subtype revealed 22 geotropic and 19 cases of apogeotropic positional nystagmus. Additionally, the study identified a rare occurrence of mixed canal involvement in one patient (1 mixed, HC+PC), indicating simultaneous BPPV-HC and BPPV-PC. Apart from BPPV, our cohort included nine patients (7.1%) diagnosed with other types of positional vertigo, which did not conform to the typical BPPV patterns (Fig. 1).
Flowchart of study. BPPV, benign paroxysmal positional vertigo; BPPV-PC, BPPV of the posterior canal; BPPV-HC, BPPC of the horizontal canal. GEO, geotropic; APO, apogeotropic; AC, anterior canal.
Clinical Characteristics of BPPV and Other Positional Vertigo
In this study, we compared the clinical and laboratory characteristics of patients diagnosed with BPPV and those diagnosed with other types of positional vertigo. The analysis involved 117 patients with BPPV and nine patients with other positional vertigo types. The mean age was similar between the BPPV group (68.5±10.5 years) and the other positional vertigo group (69.4±8.9 years), with no significant difference in age distribution (p>0.05). Both groups reported similar duration of vertigo symptoms (BPPV, 19.8±34.2 days; others, 19.7±12.9 days; p>0.05). There were no significant differences in the prevalence of previous ear disease, ear symptoms, migraine, motion sickness, or trauma between the groups. The percentage of patients with a history of BPPV was significantly higher in the BPPV groups (48.7%) compared to the other group (22.2%), although the statistical significance was not noted (p>0.05) (Table 1).
Comparison between patients with BPPV and other PV
Laboratory Findings between BPPV and Other Positional Vertigo
The BPPV group exhibited significantly higher levels of otolin-1 (350±319.1 pg/mL) than the other group (183.6±134.1 pg/mL, p=0.036) (Table 2, Fig. 2A). Average serum vitamin D levels were slightly higher in the BPPV group (20.0±11.6 ng/mL) compared to the other positional vertigo group (16.8±5.9 ng/mL). Still, this difference was not statically significant (p>0.05) (Table 2, Fig. 2B). T-scores for lumber spine and femur and CTX levels did not show significant differences between the groups (Table 2). However, there was no correlation between vitamin D and otolin-1 in serum.
Laboratory findings between patients with BPPV and other PV
(A) The serum otolin-1 is higher in benign paroxysmal positional vertigo (BPPV) than in other positional vertigo (PV), and the serum 25-hydroxy vitamin D is comparable between the two groups (B).
Clinical and Laboratory Comparison between BPPV of the Posterior Canal and BPPV of the Horizontal Canal
This study conducted a detailed comparison between two subtypes of BPPV: BPPV-PC and BPPV-HC.
There were no significant differences in age, sex, medical histories, and bone mineral density. The BPPV-PC group experienced a significantly longer duration of vertigo (25.5±42.4 days) than the BPPV-HC group (10.8±10.2 days), with a p-value of 0.009 (Table 3). Mean levels of 25(OH)-vitamin D and otolin-1 were similar between the BPPV-PC (20.1±11.1 ng/mL, 324.1±264.3 pg/mL) and BPPV-HC (19.7±12.7 ng/mL, 408.6±400.2 pg/mL) groups with no significant differences (p>0.05) (Table 4).
Clinical comparison between BPPV-PC and BPPV-HC
Laboratory findings between BPPV-PC and BPPV-HC
DISCUSSION
Our study uniquely focused on comparing serum otolin-1 levels between patients with BPPV and those with other forms of positional vertigo rather than healthy controls. We found that the mean serum otolin-1 levels were significantly higher in the BPPV group compared to the other positional vertigo group (350.1±319.1 pg/mL vs. 183.6±134.1 pg/mL; p=0.037). This indicates that elevated otolin-1 levels may be specific to BPPV rather than a general feature of all positional vertigo disorders. Previous studies have consistently shown that serum otolin-1 levels are higher in BPPV patients than in healthy individuals, suggesting otolin-1 potential as a potential biomarker for BPPV diagnosis [5,6]. In addition, by comparing BPPV patients with those having other types of positional vertigo, our study highlights that the elevated levels of otolin-1 may be specific to BPPV rather than a general feature of all positional vertigo disorders. In addition to otolin-1, vitamin D has been investigated as another biomarker for BPPV. This approach offers a more nuanced understanding of otolin-1 as a biomarker. The significant difference in otolin-1 levels between BPPV and other positional vertigo suggests that otolin-1 may help diagnose BPPV and differentiate it from other vertiginous conditions. This specificity is crucial for clinical practice, as it aids in more accurate diagnosis and tailored management strategies. When specific nystagmus is observed during symptomatic episodes of BPPV, it can be easily diagnosed through bedside examination. However, BPPV has the highest recurrence rate among vertigo conditions, and many patients do not receive an accurate diagnosis when they visit the clinic with symptoms. To overcome this, telemedicine can be utilized for diagnosis and treatment [9]. Additionally, introducing biomarker-specific BPPV could significantly aid in the current paradigm shift in BPPV management.
Our study also explored the relationship between vitamin D levels and BPPV. Several studies have shown that low serum vitamin D levels are associated with an increased risk of developing BPPV and its recurrence [10,11]. However, our study did not find a significant difference in vitamin D levels between BPPV and other positional vertigo. The absence of a significant difference in vitamin D levels between BPPV and other positional vertigo in comparison to healthy controls in previous studies may be attributed to the use of different comparison groups. Likewise, the mean 25-hydroxyvitamin D level was similar between the BPPV and central positional vertigo, and the proportions of patients with vitamin D insufficiency and deficiency did not differ significantly in the previous study [12]. While previous studies compared BPPV patients to healthy controls, our study compared BPPV to other positional vertigo patients, which might explain the observed discrepancies in vitamin D levels. Otolin-1 is a glycoprotein involved in the formation and maintenance of otoconia (calcium carbonate crystals) in the inner ear. Low vitamin D may disrupt calcium regulation, potentially contributing to otoconia degeneration and increased otolin-1 release. However, the specific relationship between serum vitamin D and otolin-1 remains unclear and requires further investigation [4,13].
Apart from otolin-1, other biomarkers have been investigated for their potential role in diagnosing vestibulopathy. These include neuron-specific enolate (NSE), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and S100B protein [14-16]. S100B protein and NSE have been studied as biomarkers to differentiate central vertigo from peripheral vertigo [14,16]. NLR and PLR were high in acute unilateral vestibulopathy, and their usefulness as prognostic markers remains unclear [15]. However, their applicability in positional vertigo requires further validation.
Our study also compared serum otolin-1 levels between different BPPV subtypes, specifically BPPV-PC and BPPV-HC. We found no significant differences in otolin-1 levels between these subtypes (Table 4). This suggests that while otolin-1 levels are elevated in BPPV patients, the levels do not vary significantly between different BPPV subtypes.
Despite the significant findings, this study has several limitations. Because the sample size for the other positional vertigo is smaller than that for the BPPV group, we employed robust statistical methods to ensure the validity of our comparisons. Specifically, we used the nonparametric test, which is less sensitive to differences in sample size. However, the sample size, particularly for the group with other types of positional vertigo, was relatively small, which may affect the generalizability of the results. Additionally, the study was conducted in a single clinical setting, potentially limiting the broader applicability of the findings. Future studies with larger and more diverse populations are needed to validate these results. Furthermore, while we measured serum otolin-1 levels at a single time point, longitudinal studies are required to understand the dynamics of otolin-1 levels over time and their correlation with disease progression and regression [5].
Notes
Funding/Support
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2024-00358977).
Conflicts of Interest
No potential conflict of interest relevant to this article was reported.
Availability of Data and Materials
All data generated or analyzed during this study are included in this published article. For other data, these may be requested through the corresponding author.
Authors' Contributions
Conceptualization, Supervision: JSH; Data curation, Funding acquisition, Methodology: KH; Formal analysis: KH, JSH; Investigation: KH, KEJ, KE, JSH; Writing–Original Draft: KH, JSH; Writing–Review & Editing: All authors.
All authors read and approved the final manuscript.