1

Introduction

Otosclerosis is a rather hereditary disease that affects the endochondral bone of the otic capsule . It is characterized by a continuous process of osteolysis and osteogenesis of the bone, vascular proliferation and connective tissue formation, initially in the area of the fissula ante fenestram of the oval window , and the possibility of proliferation toward the otic capsule and the cochlea with the risk of compromising these structures . A sequence of osteogenesis followed by ostolysis has been proposed, although it has been questioned .

Hearing loss associated with the disease is initially conductive. With progression of the disease, neurosensory component appears by a hyalinization of the spiral ligament adjacent to the otoesclerotic focus, affecting the otic capsule, interfering with the function and activity of the organ of Corti . This cochlear involvement of otosclerosis audiologically reflects as far-advanced otoesclesosis.

Far-advanced otosclerosis (FAO) affects 10% of patients with otosclerosis , usually after a first diagnosis, which is usually performed between the ages of 20 and 59 years . House and Sheehy described FAO in 1961 as a clinical otosclerosis with an air conduction threshold over 85 dB and absence of bone conduction threshold. In 1992, Iurato et al. described very far-advanced otoesclerosis (VFAO), which combines a clinical suspicion of the disease with the absence of both bone and air conduction threshold in current use audiometers. In the era of cochlear implants (CI), in addition to the previously mentioned criteria, the use of speech audiometry has taken force (speech discrimination score calculation, SDS) for the diagnosis of FAO. Merkus et al. , diagnose FAO in patients with clinical suspicion of the disease, sensorineural hearing loss, and SDS decreased (< 100%).

Radiology is fundamental in the diagnosis of patients with FAO. Several high-resolution CT (HRCT) evaluation methods have been described for the imaging analysis of patients with otosclerosis, allowing diagnosis of oval window abnormalities in 80%–90% cases (Rotteveel and Symons/Fanning ) ; with high specificity and variable sensitivity which can reach in the latter case up to 90% in cases of fenestral otosclerosis . Radiology allows diagnosis of otosclerosis in patients with an insubstantial personal and audiological history, although in many cases the diagnosis of FAO requires an exploratory surgery .

The management of patients with FAO is a challenge. Management algorithms have recently been proposed , they include two therapeutic options: stapedectomy with hearing aid adaptation or cochlear implantation.

Conducting an stapedectomy and subsequent placement of a hearing aid has been widely studied, with varying audiological results (46%–100% hearing improvement , and a 38%–75% improvement of SDS ). Classic authors stay that there are no contraindications for performing stapedectomy in any case of FAO , and on this basis some authors recommend stapedectomy with hearing aid adaptation as the first choice .

Currently, CI placement has increased in patients with FAO. There are several publications that support its use, reporting hearing improvement in 100% of cases . Cochlear implantation in patients with otosclerosis is not uncommon. Of all adult patients implanted in four centers ( n = 788), 6.7% of them had otosclerosis as the cause of deafness .

While there is a considerable amount of literature that supports the use of both treatment modalities, the ideal technique for the management of these patients is still an issue of discuss. Diverse criteria should be considered when choosing the best treatment option, including therapeutic success, economic criteria, quality, and potential complications of each of the techniques .

Placement of a CI is a technique that has been validated for the management of this condition, but has been associated with a variable rate of complications, including facial electrical stimulation and difficult insertion of the electrode bundle as an inherent condition to the pathology.

The aim of our study was to evaluate the results of cochlear implantation in patients with FAO and compare them with a control group of implanted patients with unknown origin hearing loss (UOHL). We reviewed the incidence of complications in both groups, especially toward facial electrical stimulation and difficult insertion of the electrode bundle.

2

Materials and methods

Using our database, we defined a search for patients diagnosed with far-advanced otosclerosis that were treated with cochlear implantation. We also selected a control group of patients implanted with unknown origin hearing loss (UOHL) with the same characteristics as the case group and same hearing loss duration. The audiological data access of our patients was approved by the ethics committee of our hospital.

For the diagnosis of FAO we used the criteria of House and Sheehy in addition to the revised criteria of Berrettini et al. , which includes: previous history of otosclerosis or stapedectomy, and findings suggestive of otosclerosis in TC in a binary fashion (yes/no). Members of our department operated all of patients in our hospital. Patients with unknown origin hearing loss were classified in this way after excluding known clinical and genetic forms of deafness. Genetic studies included genes encoding different connexins and mitochondrial genes. In selected cases, depending on the phenotype and family characteristics, other genes were requested.

In both groups, we analyzed demographic variables (age, sex), previous history (in the group of patients with otosclerosis: a history of otosclerosis, a family history of otosclerosis, family history of hearing loss, previous stapedectomy), otosclerosis findings on CT, surgery side, time between surgery and connection of the implant, type of surgical approach, and type and model of the implant. We also analyzed the surgical and postoperative complications, focusing on facial nerve stimulation during the device connection, subsequent changes in programming, and difficult insertion of the electrode bundle.

Measured audiological variables were the recognition of monosyllables, disyllables, CID sentences and lip reading preoperatively, and the first three variables at 6 months and 1, 2, 3 and 5 years after surgery . We also collected data after that date if available. For each period of time the pure tone average (calculated as the average dB at frequencies of 500, 1000, 2000 and 4000 Hz) was collected. When there was no answer at any of these frequencies to the maximum threshold of 120 dB of our audiometer (anacusis), we gave the numerical value of 120 dB to the corresponding frequency.

2

Materials and methods

Using our database, we defined a search for patients diagnosed with far-advanced otosclerosis that were treated with cochlear implantation. We also selected a control group of patients implanted with unknown origin hearing loss (UOHL) with the same characteristics as the case group and same hearing loss duration. The audiological data access of our patients was approved by the ethics committee of our hospital.

For the diagnosis of FAO we used the criteria of House and Sheehy in addition to the revised criteria of Berrettini et al. , which includes: previous history of otosclerosis or stapedectomy, and findings suggestive of otosclerosis in TC in a binary fashion (yes/no). Members of our department operated all of patients in our hospital. Patients with unknown origin hearing loss were classified in this way after excluding known clinical and genetic forms of deafness. Genetic studies included genes encoding different connexins and mitochondrial genes. In selected cases, depending on the phenotype and family characteristics, other genes were requested.

In both groups, we analyzed demographic variables (age, sex), previous history (in the group of patients with otosclerosis: a history of otosclerosis, a family history of otosclerosis, family history of hearing loss, previous stapedectomy), otosclerosis findings on CT, surgery side, time between surgery and connection of the implant, type of surgical approach, and type and model of the implant. We also analyzed the surgical and postoperative complications, focusing on facial nerve stimulation during the device connection, subsequent changes in programming, and difficult insertion of the electrode bundle.

Measured audiological variables were the recognition of monosyllables, disyllables, CID sentences and lip reading preoperatively, and the first three variables at 6 months and 1, 2, 3 and 5 years after surgery . We also collected data after that date if available. For each period of time the pure tone average (calculated as the average dB at frequencies of 500, 1000, 2000 and 4000 Hz) was collected. When there was no answer at any of these frequencies to the maximum threshold of 120 dB of our audiometer (anacusis), we gave the numerical value of 120 dB to the corresponding frequency.

3

Statistical analysis

We conducted a descriptive analysis of the sample by absolute and relative frequencies in the mentioned categorical variables, and median and 25th and 75th percentiles or mean and standard deviation in those numeric variables as fulfilled or not the assumption of normality.

We performed contrasts between the two groups (FAO vs UOHL) for each of the audiological variables evaluated by Mann–Whitney test, using the Bonferroni correction contrast. The differences combined between the two groups (FAO and UOHL), were evaluated by GEE analysis (generalized estimating equations).

The significance level was set at 0.05 for all contrasts. The statistical package used was SPSS 15.0 and STATA v13.0

4

Results

We found a total of 17 patients with a diagnosis of FAO who underwent CI. The personal and family history of patients that helped in the diagnoses of otosclerosis is shown in Table 1 . In the same manner we selected 17 patients with a diagnosis of unknown origin hearing loss who underwent CI; same patient characteristics were considered in both groups.

Of all patients with FAO, 4 (23.5%) were men and 13 (76.5%) women. In the UOHL group, 6 (35.3%) were men and 11 (64.7%) women. The mean age at implantation was 55.6 years in patients with FAO (p25 p75 = 47.6, 62) and 56.6 years in patients with UOHL (p25 p75 = 52.7, 61.3). The median time between surgery and the connection was 29 and 30 days respectively for FAO and UOHL ((p25 = 29, p75 = 36), ). The side of implant placement was 58.8% in the right and 41.2% in the left for patients with FAO, and 52.9% in the right and 47.1% in the left for patients with UOHL. For all these variables there were not statistically significant differences ( p > 0.05) ( Table 2 ).

Table 2

Demographic characteristics in otosclerotic and unknown origin hearing loss patients.

	Far-advanced otosclerosis	Unkwnown origin hearing loss
Sex, female/male	13/4	11/6
Age at implantation, years	55.5	56.4
Time between surgery and connection, months	34	32
Implant placement side, left/right	7/10	8/9

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