Does Oral Submucous Fibrosis Affect the Hearing Ability of an Individual? A Cross-Sectional Study in North Indian Population

Objective: To evaluate the hearing efficiency of Oral Submucous Fibrosis (OSF) patients using Pure Tone Audiometry (PTA) and to correlate between the hearing efficiency and clinical stage of OSF. Material and Methods: Twenty-five patients clinically diagnosed as OSF were evaluated for hearing loss using ‘PTA’. Patients were grouped as mild cases and severe cases. Mild cases comprised of Group A and B, and severe cases comprised of Group C and D. Patients suffering from the previous hearing were excluded from the study. The data were submitted to statistical evaluation using the Chi-square test. The level of significance was set at 5%. Results: Out of the total patients, 52.4% were diagnosed as mild cases (Group M) OSF and 47.6% as severe cases (Group S). The analysis of the data of mild cases and severe cases revealed a significant association between advancing stages of OSF and hearing loss (p = 0.026). The cases in Group M after otoscopic evaluation demonstrated no visible ear defect. However, 30% of cases in Group S showed retraction of the tympanic membrane. Conclusion: The results indicate an association between stages of OSF and hearing loss. With advancing stages of OSF, there may be involvement of muscles of soft palate namely the levator veli palatine or tensor veli palatine, which may lead to the narrowing of the Eustachian tube leading to a decrease in air conduction demonstrating it as hearing loss of varying degrees depending upon the involvement.


Introduction
Oral submucous fibrosis (OSF) is a progressive disease of the oral cavity, which was named "vidari" by the Sushruta in 600 B.C [1]. It was first described in 1952 by Schwartz, who called it "atrophia idiopathica mucosae oris" [2]. Since then, its understanding along clinical and molecular levels have increased considerately.
OSF is attributed to a variety of factors like betel nut alkaloids, capsaicin, hypersensitivity, autoimmunity, genetic predisposition, and chronic iron and vitamin B-complex deficiency, the major factor being areca nut [3]. Areca nut chewing is a common practice in the Indian subcontinent and retains its popularity as a masticatory even today.
Pindborg defined OSF as "a chronic insidious disease, affecting any part of the oral cavity and sometimes the pharynx. Although occasionally preceded by and/or associated with vesicle formation, it is always associated with a juxta-epithelial inflammatory reaction followed by fibroelastic changes of the lamina propria, with epithelial atrophy leading to stiffness of the oral mucosa and causing trismus and inability to eat" [4].
OSF is regarded as a collagen disorder causing fibrosis, and these fibroelastic changes can extend posteriorly into soft palate and nasopharynx, causing difficulty in speech. It may also involve the pharyngeal orifice of the Eustachian tube and paratubal muscles, thereby affecting its functions and causing pain along with other pathological changes in the middle ear, which can eventually lead to hearing impairment.
Pure Tone Audiometry (PTA) is an electronic device that produces pure tones and is the most common technique used for hearing assessment. It helps in identifying hearing threshold levels and also determines the type, degree, and configuration of hearing impairment [5][6][7]. The present study aimed to evaluate the hearing efficiency of OSF patients using PTA.

Study Design and Sample
A clinical cross-sectional study was undertaken in the authors' institute after obtaining the institutional ethical clearance. Twenty-five clinically confirmed cases of OSF (ears) were evaluated and graded according to the Lai DR classification [8]. All patients were tested for air and bone conduction hearing loss. Four cases were excluded from the study as the patients had OSF with middle ear defects or sensorineural hearing deficit. Informed written consent was obtained from all participating patients.

Data Collection
The patients were then divided into two groups, Mild cases (Group M) which included the Group A and B and; Severe cases (Group S) which included Group C and D [8] (Figure 1). The patients were then subjected to middle ear evaluation using otoscopy and hearing function evaluation Pesqui. Bras. Odontopediatria Clín. Integr. 2019; 19:e4745 using PTA. Apure tone audio was delivered to the ear through the headphone for assessing air conduction impairment while bone vibrator was used to evaluate bone conduction loss.

Results
Out of the total patients, 52.4% were diagnosed as mild cases (Group M) OSF and 47.6% as severe cases (Group S) of OSF, as shown in Table 1. In Group M OSF cases, 100% showed no hearing loss; whereas in Group S 40% cases showed no hearing loss, 20% showed mild hearing loss unilaterally, 30% showed mild hearing loss bilaterally, and 10% showed moderate hearing loss unilaterally.
There was a significant association between OSF groups and hearing loss (p = 0.026). The cases in Group M after otoscopic evaluation demonstrated no visible ear defect. However, 30% of cases in Group S showed retraction of the tympanic membrane. In Figure 2, the inter-group comparison of hearing loss was interpreted. It showed that as the mouth opening reduced, the hearing efficiency also decreased, concluding a significant Pearson's Rank correlations on comparison of the degree of mouth opening with hearing loss.

Discussion
Oral Submucous Fibrosis is classified under Group 1 of potentially malignant disorders; suggestive of morphologically altered tissue in which external factor is responsible for etiology and malignant transformation [10,11]. It is a chronic, an insidious disabling disease involving oral mucosa, the oropharynx, and rarely larynx [3]. Various histopathological studies have established that OSF can affect the muscular tissue in advancing stages.
The Eustachian tube is approximately 3 mm in diameter and can be divided into two parts: cartilaginous part (first two-thirds), bony part (last third, the part closest to the middle ear space).
Narrowing of the pharyngeal orifice of the Eustachian tube might be seen in OSF, leading to the failure of the Eustachian tubes to regulate air pressure effectively [12][13][14][15]. This might cause sensations of popping, clicking, and ear fullness and occasionally moderate to severe ear pain. As Eustachian tube function worsens, air pressure in the middle ear falls, and the ear feels full, and sounds are perceived as muffled [9].
The present study revealed a positive association between the advancing grade of OSF and the Eustachian tube function defect. The results obtained were in accordance with previous studies Score 0 Score 1 Score 2 Score 3 Group M Group S [6,9,16]. From the present study, it is evident that the subjective function of the Eustachian tube may be affected by the disease process.
The limitations of this study were that the sample size was small; another limitation was that the present study design is a cross-sectional one, which makes it difficult to comment on any change in hearing status.

Conclusion
Oral Submucous Fibrosis is a potentially malignant disorder, affecting structures adjacent to the oral cavity. Hearing deficit is rarely noticed but might play the role of being an important factor for patient education for an explanation of the prognostic outcome of the condition. The management for the hearing deficit in cases of OSF should primarily involve the management of the condition, which requires habit cessation to prevent the further progression of the disease along with supportive care. The present study was on smaller sample size but can be further justified by studies involving a larger sample size and patients with severe OSF.
Authors' Contributions: NS contributed to the conception and designed the study, performed the data collection, data analysis and interpretation, and wrote the manuscript, MTN contributed to the conception and designed the study, ZC and AN performed the data collection, data analysis, and interpretation, and reviewed the manuscript, N and MCV performed the data collection and reviewed the manuscript. All authors declare that they contributed to the critical review of intellectual content and approval of the final version to be published.
Financial Support: None.

Conflict of Interest:
The authors declare no conflicts of interest.