Sensorineural hearing loss and CT abnormalities in otosclerosis: Insights from otopathological specimens

Highlights

• •Otosclerosis is linked to a high rate of Sensorineural Hearing Loss (SNHL).
• •The prevalence of SNHL we found is higher than earlier reported.
• •Many otosclerosis cases with sensorineural loss may go undiagnosed, hindering care.
• •Our study offers insights to support further research in diagnosis and treatment.

Abstract

Objective

To identify audiometric profiles of otosclerosis patients and present Computed Tomography (CT) findings with their otopathological correlates using human temporal bone specimens.

Methods

We analyzed sequential patients diagnosed with otosclerosis at a university hospital. Each patient underwent hearing evaluations and CT scans. We assessed the type and severity of hearing loss and the presence and location of otosclerotic foci. Audiometric results and CT images were compared. Additionally, representative otopathological specimens from the Paparella Otopathology & Pathogenesis Laboratory were examined to understand the impact of otosclerotic foci on cochlear and inner ear structures.

Results

The study included 40 patients (25 female, 15 male; mean age 50.9 years, range 24–72). Most patients were white (62.5%), with others being black (35%) or Asian (2.5%). Symptoms typically began at age 36.4 years, with an average disease duration of 14.3 years. Audiometric analysis of 71 ears (excluding 9 previously operated) showed mixed hearing loss in 64.78%, sensorineural loss in 23.94%, conductive loss in 2.81%, and normal hearing in 8.45%. Our data revealed a significantly higher prevalence of sensorineural hearing loss among patients with otosclerosis compared to previous reports. This disparity may be due to our higher diagnostic rate, as CT scans were used for patients with unexplained sensorineural hearing loss, and the longer disease course related to delayed specialist access caused by structural issues in the Brazilian health system. Relevant CT findings are presented and compared with similar otopathology specimens.

Conclusions

Our study highlights a higher prevalence of mixed and sensorineural hearing loss in patients with otosclerosis than previously reported, suggesting that otosclerosis may be associated with more significant auditory impairment than commonly recognized. However, given the limitations of our retrospective design and the potential influence of co-morbidities, these findings should be interpreted with caution.

Level of evidence

2.

Introduction

Otosclerosis is a condition characterized by abnormal bone remodeling in the otic capsule.¹ It affects, in the United States only, over 3 million people.² Typically, the otic capsule experiences minimal to no bone remodeling over a person's lifetime.¹ However, various molecular, genetic, and environmental factors can disrupt the processes that usually prevent such remodeling.2, 3 This disruption can lead to abnormal bone resorption and new bone formation.⁴ Consequently, the altered bone architecture may cause hearing loss either through the fixation of the stapes or by direct invasion of the cochlear endosteum.⁵

Otosclerosis is well-known for causing conductive hearing loss by either narrowing the oval window, creating extrinsic fixation, or directly fixing the stapes footplate.1, 5 However, recent evidence indicates that otosclerosis can also lead to sensorineural hearing loss, especially when otosclerotic foci invade the cochlear endosteum.4, 6 Although once considered rare, recent studies have shown that up to a third of patients with otosclerosis may develop clinically significant sensorineural hearing loss, which exceeds what would be expected from normal aging alone.7, 8 The otopathological correlates of sensorineural hearing loss due to otosclerosis include the invasion of the cochlear endosteum by otosclerotic foci, with or without noticeable changes in cochlear architecture. Other pathological changes may include hyalinization of the spiral ligament, atrophy of the stria vascularis, and loss of cellular structure in the Organ of Corti.¹ Although the exact molecular mechanisms underlying the occurrence of these pathologic changes, the hyalinization of the spiral ligament is thought to result from increased expression of TGF-beta due to the local inflammatory process.⁴ Additionally, the loss of cochlear hair cells is likely associated with abnormal ion concentrations in the endolymph, which occur secondary to changes in the lateral wall.⁴

Although otosclerosis has been extensively studied, reports on the true prevalence of mixed or pure sensorineural hearing loss secondary to otosclerosis are limited. For cases of pure sensorineural hearing loss, a high level of suspicion is needed to consider otosclerosis as a differential diagnosis, given that less than 1% of all otosclerosis cases result in pure sensorineural hearing loss.4, 5 In this context, our outpatient clinic is uniquely positioned to investigate such cases. Patients with sensorineural hearing loss of unclear origin undergo Computed Tomography (CT) of the temporal bones to evaluate less common causes of hearing loss (e.g., bony inner ear malformations). Our team, consisting of experienced otologists and radiologists, is well-equipped to conduct these investigations. Therefore, the aim of our study is to identify the audiometric profiles of patients with otosclerosis at a tertiary hospital and to present significant CT findings along with their otopathological correlates using human temporal bone specimens.

Methods

Patient selection

From the otology outpatient clinic of a university hospital, all patients diagnosed with otosclerosis between February 2020 and December 2021 were sequentially selected. The study was approved by the institutional ethics review board of our institution (nº 0035/2020).

Patients with otosclerosis were included based on clinical, audiologic, and imaging criteria, specifically audiometric tests indicating conductive, mixed, or sensorineural hearing loss. Ears who undergone stapes surgery were excluded from the analysis. All patients underwent CT imaging of the temporal bone. According to our clinical practice protocols, CT scans were ordered either to confirm the diagnosis, for pre-surgical planning, or to aid in differential diagnosis. Standard audiometry was performed on all selected patients to classify the type of hearing loss. Race was self-reported by participants during data collection.

Inclusion criteria were defined as patients diagnosed with unilateral or bilateral otosclerosis based on clinical, audiological, or imaging findings. Exclusion criteria included: sensorineural hearing loss attributable to causes other than otosclerosis; absence of otosclerotic foci on the CT scan; contraindications to the proposed imaging exams; and patients who had undergone previous ear surgeries, except for ventilation tube placement or stapedotomy.

CT scan analysis

We evaluated several aspects of the temporal bone using axial, coronal, and sagital CT images, including: a) Otosclerotic focus location; b) Fenestral focus (oval window): presence or absence of a fenestral focus; involvement of the cochlear endosteum; c) Thickness of the stapes footplate: total or partial obliteration, and anterior or posterior thickening; d) Round window: partial or obliterative otosclerotic focus.

The analysis of CT scans was conducted by two otolaryngologists (Otolaryngologist #1 and Otolaryngologist #2) and a radiologist specializing in head and neck imaging (Radiologist #3). Agreement between their evaluations was statistically analyzed. For patients who had previously undergone stapedotomy with a metallic prosthesis, we assessed whether any resulting CT artifact obscured anatomical landmarks. If such artifacts hindered the measurement of specific landmarks, those landmarks were not evaluated in the affected ear.

Most of the images (87.5%) were obtained using the Multislice Phillips CT scanners BRILLIANCE™, 64-channel, first generation (v2.6.2.22004-02/24/2013). Some patients already had previous recent exams on DVDs that were brought to the appointment (12.5%); for these patients, CT scans were not repeated to avoid unnecessary exposure to radiation. Images were acquired with high resolution parameters, and readings with a Window Width (WW) 4000 and Window Level (WL) of 500 and thickness of 0.3 to 0.6 mm. Exams were evaluated using the Radiant DICOM viewer 2020.2 (64-bit) program, using axial, coronal, and sagittal slices. Screen resolution at 1366 × 768 pixels.

Otopathological specimens

From the Paparella Otopathology & Pathogenesis Laboratory at the University of Minnesota, we selected human temporal bones from donors with otosclerosis. From the database of over 260 cases of otosclerosis, we carefully selected specimens that presented with similar otosclerotic foci as ones from the CT scans from the donors we included in our study. The temporal bones had been previously harvested during autopsy, fixed in 10% formalin, decalcified using EDTA, embedded in celloidin, and then sectioned at the horizontal plane at a 20 μm thickness. Every 10th section was stained in hematoxylin and eosin, mounted in glass slides, and stored in an archive. Studies using our archival collection of human temporal bones are considered exempt from institutional review board (ID: STUDY00003249).

Statistical analysis

We analyzed the data for our study, focusing on several key variables, including age, sex, type of hearing loss, and degree of hearing loss. The data was presented in terms of frequency for categorical variables and as averages for continuous variables. The interobserver agreement analysis for categorical variables was performed using Cohen's Kappa, and for the continuous variable ‘niche size”, the intraclass correlation coefficient was used, with the following interpretation: < 0 No agreement; 0‒0.20 Poor agreement; 0.21‒0.40 Fair agreement; 0.41‒0.60 Moderate agreement; 0.61‒0.80 Substantial agreement; and 0.81–1 Almost perfect agreement. All tests were two-tailed, and p-values < 0.05 were considered statistically significant. The statistical analyses were conducted using SPSS software (IBM Corp. SPSS Statistics for Windows, version 24.0. Armonk, NY).

Results

Clinical profile

The study included 40 patients with otosclerosis (female, n = 25, 62.5%; male, n = 15, 37.5%). The average age of the patients was 50.9 years, with a standard deviation of 12.3 years, and ages ranged from 24 to 72 years. Most patients identified as white (62.5%); other racial categories included black (35%) and Asian (2.5%) (Table 1).

Table 1.

Clinical profile of our population of patients with otosclerosis.

Variables	n = 40
Age	50.9 ± 12,3
Sex
Female	25 (62.5%)
Male	15 (37.5%)
Race
White	25 (62.5%)
Black	13 (35%)
Asian	1 (2.5%)
Initial symptoms
Age of onset (years)	36.4 ± 13,0
Duration of disease (years)	14.57 ± 12,46
Vertigo	0 (0%)
Dizziness	4 (10%)
Disequilibrium	2 (5.0%)
Tinnitus	22 (55%)
Hearing loss	26 (65%)
Comorbidities that associated with the onset of disease
Gestation	6 (15%)
Infection	3 (7.5%)
Measles	11 (28%)
Other	1 (2.5%)
Prior history
Family history of hearing loss
Yes	18 (46%)
No	21 (54%)
Hypertension	14 (35%)
Diabetes mellitus	10 (25%)
Hypothyroidism	5 (12%)
Dyslipidemia	5 (12%)
Other	5 (12%)

The average age at which symptoms first appeared was 36.4 years, and the average duration of the disease was 14.3 years (Table 1). At the onset of otosclerosis, 26 patients (65%) experienced hearing loss, 22 patients (55%) reported tinnitus, and 6 patients (15%) had symptoms of imbalance and dizziness. Factors associated with the onset of symptoms included pregnancy for 6 patients (15%), an otological infection for 3 patients (7.5%), and other factors for 1 patient (2.5%). Additionally, 11 patients (28%) had a history of measles, none of which reported any hearing loss prior to the onset of the progressive hearing loss that associated with otosclerosis. Nearly half of the patients, 18 (46%), had a positive family history of otosclerosis. Other relevant medical history included hypertension in 14 patients (35%), diabetes mellitus in 10 patients (25%), hypothyroidism in 5 patients (12%), and dyslipidemia in 5 patients (12%).

Regarding treatments for otosclerosis, none of the patients used sodium fluoride. However, 22 patients (55%) had used bisphosphonates, specifically sodium alendronate. Of these, one-third used the medication for 3 months, 8 patients (36%) used it for 6 months, 5 patients (23%) used it for more than 1 year, and 1 patient (4.5%) used it for 1 year. Seven patients (18%) had previously undergone stapedotomy or stapedectomy (Table 2).

Table 2.

Treatment and physical examination.

Treatment
Drug treatment
Bisphosphonates	22 (55%)
None	18 (45%)
Time under medication
3 months	8 (36%)
6 months	8 (36%)
1 year	1 (4.5%)
>1 year	5 (23%)
Physical examination
Otoscopy
Normal	24 (60%)
Abnormal	16 (40%)
Tympanic membrane retraction
None	25 (62%)
Grade I	none(38%)

Regarding the physical examination of the patients (Table 2), 24 patients (60%) had normal otoscopic findings, while 16 patients (40%) showed abnormalities. Among these, one case had opacity, one case had tympanosclerosis with retraction in both ears, and one case had a monomeric tympanic membrane. Tympanic membrane retraction was observed in 15 patients (38%), all of whom had the mildest form of retraction, classified as Grade I.

Each ear was analyzed separately for type and degree of hearing loss. Seventy-one ears were deemed eligible for audiometric evaluation, as nine ears had already been operated on and had to be excluded. The majority of the ears had mixed hearing loss, with 46 ears (64.78%). Sensorineural hearing loss was observed in 17 ears (23.94%), and conductive hearing loss was present in 2 ears (2.81%). Six ears (8.45%) had normal hearing (subclinical foci).

Regarding the degree of hearing loss, 21 ears (29.57%) had moderate hearing loss, 20 ears (28.16%) had moderately severe hearing loss, 9 ears (12.67%) had mild hearing loss, 8 ears (11.26%) had severe hearing loss, 5 ears (7.04%) had complete hearing loss, and 2 ears (2.81%) had profound hearing loss. These data are presented in Table 3.

Table 3.

Audiometric profile.

Type of hearing loss	n = 71
Normal thresholds	6 (8.45%)
Conductive	2 (2.81%)
Mixed	46 (64.78%)
Sensorineural	17 (23.94%)
Degree of hearing loss
Normal thresholds	6 (8.45%)
Mild	9 (12.67%)
Moderate	21 (29.57%)
Moderate to severe	20 (28.16%)
Severe	8 (11.26%)
Profound	2 (2.81%)
Complete	5 (7.04%)

Table 4 describes the location and characteristics of the otosclerotic foci as seen in CT scans and a comparative analysis between examiners. Most patients presented with bilateral otosclerosis foci. Involvement of the oval window and stapes footplate were more common than involvement of the round window (Table 4).

Table 4.

Location and characteristics of the otosclerotic foci.

Variables	Evaluator 1	Evaluator 2	Evaluator 3	Kappa	Concordance	p
Affected ear	n = 40 patients	n = 39 patients	n = 40 patients	0.58	84.62%	<0.001
Bilateral	36 (90%)	32 (82.05%)	35 (87.5%)
Left	3 (7.5%)	1 (2.56%)	2 (5%)
Right	1 (2.5%)	5 (12.82%)	2 (5%)
Oval window	n = 79 ears	n = 78 ears	n = 80 ears	0.56	57.89	< 0.001
No cochlear endosteum involvement	51 (64.55%)	49 (62.82%)	47 (58.75%)
Cochlear endosteum involvement	24 (29.11%)	21 (26.92%)	22 (27.5%)
No oval window focus	4 (5.06%)	8 (10.25%)	11 (13.75%)
Round window	n = 80 ears	n = 78 ears	n = 80 ears	0.55	78.95	<0.001
Partial involvement	3 (3.75%)	6 (7.69%)	11 (13.75%)
Obliteration	6 (7.5%)	2 (2.56%)	8 (10%)
Absent	71 (88.75%)	70 (89.74%)	61 (76.25%)
Stapes footplate	n = 79 ears	n = 76 ears	n = 79 ears	0.11	13.89	0.019
Complete thickening	33 (41.77%)	29 (38.15%)	27 (34.17%)
Anterior focus	41 (51.89%)	20 (26.31%)	33 (41.77%)
Posterior focus	0 (0%)	1 (1.31%)	0 (0%)
Obliteration	0 (0%)	0 (0%)	8 (10.12%)
No involvement	5 (6.32%)	26 (34.21%)	11 (13.92%)

Audiometric, imaging, and otopathological correlations

Some representative otosclerotic lesions detected in the CT images of the patients in this study were selected and correlated with the audiometric examination of the respective ear and histological images to illustrate and facilitate the visualization of the otosclerotic focus in the tomography. The most significant findings and their respective imaging/Otopathological correlates are listed below

Conductive hearing loss

Fig. 1 represents the case of a patient who presented conductive hearing loss as the most important component of his hearing loss. The CT scan revealed the presence of a single focus located in the region of the fissula ante fenestra without compromising the cochlear endosteum. In the associated Otopathological specimen, a focus in the same region is represented, without any major impact in the cochlear neurosensory epithelium.

Fig. 1.

Representative CT scan (A) and audiogram (C) from a patient who had otosclerosis and presented with hearing loss with a conductive component. The CT scans show a fenestral focus (black arrow) causing fixation of the footplate. The histology specimen (B) represents an Otopathological correlate of the CT finding, showing the presence of a fenestral focus (black arrow) wedging the footplate within the oval window, without a cochlear component.

Mixed hearing loss

Fig. 2 represents the case of a patient who presented with severe mixed hearing loss in their audiogram. The CT scan reveals a single focus located at the region of the fissula ante fenestra that invaded the cochlear endosteum. A representative human Otopathological specimen is also depicted, showing a similar type of focus that caused fixation of the footplate stapes and invaded the cochlear endosteum.

Fig. 2.

Representative CT scan (A) and audiogram (B) from a patient who had otosclerosis and presented with mixed hearing loss. The CT scan shows a fenestral focus causing fixation of the footplate (black arrow) and invading the cochlear endosteum (black circle). The histology specimen (C and D) represents and Otopathological correlate of the CT finding, showing similar findings as the CT scan. Image (D) shows the invasion of the cochlear endosteum seen in a higher magnification.

Pure sensorineural hearing loss

Pure sensorineural hearing loss secondary to otosclerosis is described in the literature as a rare finding. However, we observed that – among our donors – 23% had pure sensorineural hearing loss, which could represent that this clinical association is not commonly identified as otosclerosis is more commonly associate with conductive or mixed hearing loss. Fig. 3 is representative of a patient who had a pure sensorineural hearing loss in their audiogram. As the patient had a large family history of hearing loss at a young age, a CT scan was ordered and revealed the presence of a fenestral otosclerosis focus that affected the cochlear endosteum.

Fig. 3.

Representative CT scan (A) and audiogram (B) from a patient who had otosclerosis and presented with sensorineural hearing loss. The CT scan shows a fenestral focus (black arrow) that invades the cochlear endosteum (black circle). The histology specimen (C and D) represents and Otopathological correlate of the CT finding, showing the presence of a fenestral focus that invades the cochlear endosteum but does not cause fixation of the stapes. Image (D) shows the lack of stapes involvement and invasion of the cochlear endosteum seen in a higher magnification – hyalinization of the spiral ligament can be observed in this image.

Cochlear otosclerosis causing severe cochlear structural defects and profound hearing loss

Fig. 4, Fig. 5 are representative of a patient who presented with bilateral profound hearing loss; their CT scan revealed the presence of both fenestral and cochlear foci of otosclerosis with significant structural impact to the cochlear architecture on both ears. The representative Otopathological specimens show the presence of a combined fenestral and cochlear foci. There is severe cochleovestibular hydrops associated, which clinically correlate with the presence of vestibular symptoms. There is an associated partial ossification of the basal turn of the cochlea, as well as loss of the structural integrity of the organ of Corti.

Fig. 4.

Representative CT scan (A) and audiogram (B) of the left ear from a patient who had cochlear otosclerosis and presented with profound hearing loss. The CT scan shows both cochlear foci that invades the endosteum and compromises the normal cochlear architecture (black arrow) and a fenestral focus that wedges the footplate within the oval window. The histology specimen (C and D) represents and Otopathological correlate of the CT finding, showing the presence of both cochlear and fenestral foci with severe architectural changes, similar to those seen in the CT scan. Image (D) shows the cochlea seen in higher magnification, showing severe changes in the cochlear duct, including hyalinization of the spiral ligament and complete atrophy of the stria vascularis (1), severe hydrops (2), and complete loss of the organ of Corti (3).

Fig. 5.

Representative CT scan (A) and audiogram (C) of the right ear ear from a patient who had cochlear otosclerosis and presented with profound hearing loss. The CT scan shows both cochlear foci that invades the endosteum and compromises the normal cochlear architecture (black arrow) and a fenestral focus that wedges the footplate within the oval window. The histology specimen (B) represents and Otopathological correlate of the CT finding, showing the presence of both cochlear and fenestral foci with severe architectural changes, similar to those seen in the CT scan.

Obliteration of the round window membrane

Fig. 6 is representative of a patient who presented both fenestral and round window foci of otosclerosis in their CT scan. Audiogram revealed a mixed hearing loss. It is important to identify the presence of a complete round window blockage secondary to otosclerosis as it can result in failure to close the air-bone gap following stapedectomy. The Otopathological specimen is representative of a complete round-window obstruction secondary to the otosclerotic foci.

Fig. 6.

Representative CT scan (A) and audiogram (C) of the left ear ear from a patient who had cochlear otosclerosis and presented with mixed hearing loss. The CT scan shows an otosclerotic focus obliterating the round window. The histology specimen (B) represents and Otopathological correlate of the CT finding, showing the presence of round window obliteration.

Other significant CT-otopathological correlations

Other CT scans demonstrated other significant findings that are relevant both on the clinical and surgical standpoints. Fig. 7, for example, represents a patient who had mixed hearing loss in their audiogram. Their CT scan showed a significant obliteration of the oval window. An Otopathological specimen with similar findings is included for comparative purposes. Fig. 8 is representative of otosclerotic foci affecting the peripheral vestibular organ, specifically the region around the saccule and the posterior semicircular canal.

Fig. 7.

This image is representative of a patient who presented with an obliterative fenestral focus (A) and mixed hearing loss (C). The Otopathological specimen (B) reveals findings that are similar to those of the CT scan.

Fig. 8.

CT scan (A) and audiogram (C) from a patient with advanced otosclerosis affecting the cochlear endosteum (top arrow), the area surrounding the saccule, and the posterior semicircular canal (bottom arrow). Their audiogram revealed mixed hearing loss (C). The representative histological section (B) reveals similar findings, showing otosclerotic foci affecting both the cochlear and vestibular organs.

Discussion

The study reveals a notably high prevalence of both sensorineural and mixed hearing loss among patients with otosclerosis, which significantly contrasts with existing literature. Specifically, we found mixed hearing loss in 64.78% of ears and sensorineural hearing loss in 23.94%, totaling 88.72% of our sample. These figures are considerably higher than the 20 %–30 % prevalence reported in prior studies.8, 9, 10 Several factors may contribute to this discrepancy. First, our group systematically conducts comprehensive imaging tests, including CT scans, to diagnose less common causes of sensorineural hearing loss, such as bony inner ear malformations. This thorough approach may have led to identifying cases that might otherwise remain undiagnosed. Also, our sample may include a higher proportion of patients with advanced or atypical forms of otosclerosis, leading to increased prevalence of sensorineural and mixed hearing loss. In Brazil’s public health system, delays in specialist consultation often result in patients only reaching specialists after significant disease progression.11, 12 This delay might partly explain the higher prevalence of sensorineural hearing loss in our cohort, which has an average age of 50 years. Hearing loss in high frequencies is commonly described in patients in their 50 s and 60 s.13, 14 Although age influences these results, our data show that 80% of patients had at least moderate hearing loss, with 21% experiencing severe to profound loss. This suggests that the degree of hearing loss in our study is more severe than what would be expected from age-related hearing loss alone. Nonetheless, these results should be interpreted with caution. Since this study represents sequential patients diagnosed with otosclerosis, it is possible that confounding variables may have influenced the outcomes.

Our study's average age of symptom onset was 36.4 years, aligning with existing literature,¹⁵ but the average disease duration of 14.3 years indicates that patients experienced a longer disease course before diagnosis as compared with previous studies (range: 1.8–4 years).¹⁵ This supports our observation that in Brazil, patients often experience significant delays in seeing a specialist, which postpones diagnosis and treatment and increases the risk of complications and sequelae. This extended delay likely contributes to the more severe audiometric profiles observed. Additionally, the high prevalence of tinnitus (55%) and imbalance symptoms (15%) in our patient cohort suggests a broader range of otosclerotic symptoms.

Regarding treatment strategies, none of our patients used sodium fluoride, but 55% had been treated with bisphosphonates. The rationale behind the use of bisphosphonates in patients with otospongiosis and progressive hearing loss is that these drugs interact with osteoclast metabolism to induce osteoclast apoptosis, therefore inhibiting bone resorption.¹⁶ Additionaly, the reduced inflammatory response and resulting production of toxic enzymes secondary to abnormal bone metabolism is reduced.¹⁶ The efficacy of bisphosphonates in treating otosclerosis remains debated, and varying durations of therapy among patients could influence outcomes.⁹ Recent studies in small populations demonstrated that bisphosphonates can stabilize the progression of sensorineural hearing loss in patients with otosclerosis.9, 17, 18, 19 Further research should further explore the relationship between bisphosphonate therapy and hearing loss progression in patients with otosclerosis.

Additionally, we compared CT imaging findings with otopathological specimens from human temporal bones affected by otosclerosis. The presented imaging-otopathological correlates of the otosclerotic lesions exemplify how the otosclerotic foci cause significant alterations in cochlear architecture.1, 2, 3 These changes align with the observed sensorineural hearing loss, highlighting the impact of otosclerotic involvement on cochlear function.1, 5 This comparative approach enhances our understanding of the pathophysiological mechanisms underlying sensorineural hearing loss in otosclerosis and emphasizes the need for thorough diagnostic evaluations.

The higher prevalence of mixed and sensorineural hearing loss in our study underscores the need for thorough audiometric evaluations in otosclerosis patients. It also highlights that CT scans can be a valuable tool for diagnosing cochlear otosclerosis in cases where stapes involvement is not present, especially in patients with unexplained sensorineural hearing loss. Given the risks associated with unnecessary CT scans, future research should aim to identify diagnostic clues and develop protocols to pinpoint cochlear otosclerosis as the cause of sensorineural hearing loss, thereby reducing the indiscriminate use of CT scans. Our data suggests that otosclerosis may lead to more severe auditory impairment than previously recognized, potentially affecting decisions regarding surgical or pharmacological interventions. Future studies should investigate the underlying causes of these discrepancies in hearing loss prevalence, conduct longitudinal research to understand hearing loss progression and treatment effects, and explore genetic and environmental factors influencing otosclerosis severity. Additionally, examining otopathological specimens from patients treated with bisphosphonates could help clarify how these drugs might mitigate sensorineural hearing deficits.

While this study accurately reflects the population seeking medical care for otosclerosis, its observational nature limits our ability to draw definitive conclusions about the direct association between otosclerosis and the degree of sensorineural hearing loss. As such, future prospective clinical and experimental studies are necessary to corroborate our findings. Although our study provides valuable insights into the hearing and imaging aspects of long-standing otosclerosis, it has some limitations. While the sample size is adequate for the intended analysis, it is representative of the patients seeking care for otosclerosis at our outpatient clinic and may not fully represent the broader otosclerosis population. As a result, some variables, such as age and the presence of other comorbidities that could impact the development of sensorineural hearing loss, could not be fully controlled for. Additionally, the retrospective design and reliance on patient-reported data may introduce biases. Therefore, prospective studies with larger, more diverse populations are needed to validate our results and further explore the trends observed.

Conclusion

Our study highlights a higher prevalence of mixed and sensorineural hearing loss in patients with otosclerosis than previously reported, suggesting that otosclerosis may be associated with more significant auditory impairment than commonly recognized. However, given the limitations of our retrospective design and the potential influence of co-morbidities, these findings should be interpreted with caution. Further research, particularly prospective studies, is needed to explore the factors influencing the severity of hearing loss in otosclerosis and to refine diagnostic and management strategies for individuals affected by this condition.

Ethical statement

This study was approved by the institutional ethics review board of Universidade Federal de São Paulo – UNIFESP (nº 3.950.246 ‒ project 0035/2020). Studies in Human Temporal Bones are considered exempt from institutional review board (ID:STUDY00003249).

Funding

This study was funded by NIH NIDCD U24 DC020851-02 (United States) and in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance code 001.

Declaration of competing interest

The authors declare no conflicts of interest.