Abstract
Background
Hearing distortions from trauma to the ear could occur by direct perforation of the tympanic membrane.
Aim
To characterize hearing thresholds in patients with traumatic tympanic membrane perforation and changes in hearing occurring in the course of treatment.
Study design
Prospective analytical study
Setting
Olabisi Onabanjo University Teaching Hospital, Sagamu, Nigeria.
Methodology
We prospectively entered in a proforma the demographics of 60 patients with traumatic tympanic membrane perforation at the teaching hospital in Sagamu, Nigeria over a period of five years as well as their hearing assessment with pure tone audiometry at initial contact and six weeks post-injury. The type of hearing loss, pure tone average and air-bone gaps were recorded. Hearing changes between initial and second audiometric assessments were analyzed and compared.
Results
The data obtained from 60 patients with 73 traumatized ears were analyzed. In all, 64 (87.7%) of the ears had hearing loss while 33(45.2%) had conductive hearing loss. Injured ears had significantly worse hearing and higher air-bone gaps ABGs compared with non-traumatized ears. There was notable improvement in hearing thresholds and closure of air-bone gaps in the course of treatment, which was significantly more at the low frequencies compared with the high frequencies.
Conclusion
Patients with traumatic tympanic membrane perforation majorly had conductive hearing loss in the injured ears with audiometric confirmed air-bone gaps and increased hearing thresholds which were not frequency dependent. There was appreciable improvement in hearing parameters over time, significantly more at the low frequencies.
Keywords: Trauma, Tympanic membrane perforation, Hearing changes
Introduction
Hearing in humans is an interplay of many factors, including efficient and effective sound conduction through different media from the external into the inner ear, and also from the inner ear to the central processing area in the superior temporal gyrus in the brain. Most of hearing occur through the conduction of sound from the external auditory canals to set the tympanic membrane (TM) into vibration. The TM serves as the initiation point of the transformer mechanism of the middle ear, which processes sound into the inner ear.
The ear is the most common organ affected by blast injury because it is the body's most sensitive pressure transducer1. Hearing distortions from trauma could occur by direct impact on the delicate soft tissues of the cochlea such as concussion in the inner ear. Labyrinthine concussion is a term used to describe a rare cause of sensorineural hearing loss with or without vestibular symptoms occurring after head trauma2. Labyrinthine concussion may also be associated with temporal bone fractures especially of the oblique type, with or without perforation of the tympanic membrane, and in the ear contralateral to the injured one3. A perforation of the ear drum is an unequivocal sign of a significant middle ear trauma. The hearing impairment is usually more because of the disruption of the sound conducting mechanisms causing a conductive or sensorineural hearing loss. Diagnosis of labyrinthine concussion also relies on audiometric tests, which reveal characteristic tracings reminiscent of acoustic trauma3.
Traumatic injuries to the tympanic membrane are common and have varied etiologies. Etiological factors of TTMP which vary between people and their daily activities, include use of cotton swab for cleansing the ear, high diving, and assaults4. Slaps by spouse or lover, parents, sibling, school teachers, schoolmate, state police and prisoner appear to be common among all climes of people5. Most of the injuries heal spontaneously with minimal medical or surgical intervention5. Despite the healing, there may be morbidities in patients with complaints ranging from tinnitus, nystagmus, vertigo, to difficulty in hearing. Traumatic injuries to the ear can sometimes be a subject of litigation. In such situations, hearing impairment must be confirmed by hearing threshold measurements. Furthermore, hearing loss must be proven to be a consequence of the trauma, since other forms and causes of hearing impairment can occur.
Hearing pre-evaluation and serial monitoring could be invaluable in determining qualification for compensation in ear injuries. Compensation is awarded based on the severity and degree of hearing loss, and extent of the functional impairment over time6.
The study aims to characterize hearing thresholds in patients with traumatic tympanic membrane perforation (TTMP) and explore dynamic changes in hearing that occur in the course of treatment. This study should provide basic information of our experience on TTMP, stimulate changes or reinforce our practice based on clinical evidence.
Patients & Methods
This is a prospective analytical study on patients that were diagnosed with traumatic perforations to the tympanic membrane over a five-year period, ranging from January 2012 to December, 2016.
The patients were managed at the Ear, Nose and Throat (ENT) clinic and the Accident and Emergency Centre of Olabisi Onabanjo University Teaching Hospital (OOUTH), Sagamu, Nigeria. Patients’ diagnoses were made based on the history of trauma to the ear, and examination for confirmation of perforation, tear or rupture of the tympanic membrane consequent upon the trauma. Patients were informed about the study and its implications, including the fact that their declining of participation would not affect their treatment, and those that consented had their data included in the study.
Information obtained from the patients included age, sex, and the traumatized ear. Hearing assessment was performed with pure tone audiometry (PTA) in both ears, at frequency ranges of 0.25-8.0kHz for the air conduction, and 0.25-4.0kHz for bone conduction thresholds. Audiometry was performed at the first contact (PTA1) and subsequently at least six weeks after the injury (PTA2) when healing of the tympanic membrane is expected to have been established in the patients. Our patients were managed with non-active medical intervention (masterly-inactivity) that comprised leaving the ear (no ear cleaning nor toileting, no otic-drops), prescription of systemic antibiotics and analgesics as indicated, with ascorbic acid to aid healing of the traumatized tympanic membrane). Particular parameters noted on the audiograms included the type (described as normal hearing, conductive, sensorineural and mixed hearing loss), the pure tone average (PTAv) at all frequencies (0.25-8.0kHz), subdivided into low (0.25-1.0kHz), and high frequencies (2.0-8.0 kHz) for the air conduction. The air-bone gaps (the difference between the air-conduction and bone conduction hearing thresholds) were calculated for all (0.25-4.0kHz), low (0.05-1.0kHz) and high frequencies 2.0-4.0 kHz).
Other patients excluded from the study were those that had previous histories of hearing impairment, those with previous suppurative ear diseases and those with tympanic membrane perforations from other causes. Data of patients with incomplete audiometric evaluations (either initial or subsequent audiometry) were also excluded. Ethical approval for the study was obtained from the Health Research Ethics Committee (HREC) of OOUTH, Sagamu, Nigeria.
The hearing changes (dynamics) between the initial and second audiometric evaluation were analyzed and compared. The hearing thresholds degree was classified according to American speech and hearing association (ASHA) guidelines , as normal, PTAv of 0-25dBHL, mild 25.1-40.0 dB HL, while any hearing loss >40.1 was moderately-severe.
The data obtained was presented in tabular form. Descriptive analyses of the patients was done, while inferential comparative statistics was performed in the hearing threshold parameters between the injured and the contralateral ear, initial and second audiometric parameters, and the two frequency groups. Data analyses was performed using Statistical package for social sciences (SPSS) version 20, and level of statistical significance was set at p<0.05.
Results
One hundred and seven patients had traumatic tympanic membrane perforation, while 60 of them had enough data for analyses. The ages ranged from 8-71 years; Mean ± SD was 33.4 ±12.9 years. There were 35 males (58.3%) and 25 females (41.7%). The right ear was traumatized in 21 (35.0%), left in 26 (43.3%) while 13 patients (21.7%) had both ears traumatized.
The duration between ear injury and initial audiometric evaluation, ranged between 1-9 (Mean ± SD= 4.1 ±2.4) days. Hearing level was normal in the injured ears in 9 (12.3%) patients, and in 21 (44.7%) ears that were not traumatized. Most of the injured ears (45.2%) had conductive hearing loss, 27.4% had sensorineural and 15.1% had mixed hearing loss. Similarly, there were different levels and degrees of hearing loss in 64 (88.7%) of the injured ears compared to the 26 (55.2%) of the contralateral ears. There were statistically-significant differences in the hearing thresholds in the injured ears compared with those of the contralateral ears. The ABGs also revealed significantly higher gaps in all frequencies between the injured and the contralateral ears. The details of the audiometric parameters of the patients is shown in Table 1.
Table 1: Audiometric parameters of 60 patients.
| Parameter | Injured ear | Contralateral ear |
| Type of audiometry | n=73 (%) | n=47 (%) |
| Normal | 9 (12.3) | 21 (44.7) |
| Conductive hearing loss | 33 (45.2) | 3 (6.3) |
| Sensorineural hearing loss | 20 (27.4) | 17 (36.2) |
| Mixed hearing loss | 11 (15.1) | 6 (12.8) |
| Degree of hearing loss(dBHL) | ||
| Normal(0-25.0) | 9 (12.3) | 21 (44.7) |
| Mild (25.1-40.0) | 47 (64.4) | 23 (48.9) |
| Moderate and above (≥40.1) | 17 (23.3) | 3 (6.3) |
| Pure tone average, PTAv in dBHL | ||
| Low frequency (0.25-1.0kHz) | 28.7 | 17.9 |
| High frequency (2.0-8.0 kHz) | 39.1 | 31.7 |
| All frequencies (0.25-8.0 kHz) | 33.9 ±7.4 | 24.8 ±5.8 |
| Statistics | t=12.354 | p<0.001 |
| Air-bone gap, ABG in dBHL | ||
| Low frequency (0.25-1.0kHz) | 15.7 | 6.8 |
| High frequency (2.0-4.0 kHz) | 10.1 | 6.1 |
| All frequencies (0.25-4.0 kHz) | 12.9 ±4.1 | 6.5 ±3.8 |
| Statistics | t=11.296 | p<0.001 |
The audiologic changes occurring during the course of treatment revealed that hearing improved in 65 out of the 73 traumatized ears , with magnitude of ≥5dBHL in 58 ( 79.5%) ears , and of <5dBHL in 7 (9.6%) ears, while hearing impairment worsened in 8 ears (11.0%). Table 2 depicts the audiologic changes occurring in the course of treatment in the 65 ears with improved hearing compared with the initial values. The time of subsequent audiometric assessment (PTA2) varied between 43 and 57days post-trauma (Mean ± SD was 47.3 ± 3.9). There was significant improvement in the hearing thresholds in all frequencies in the course of treatment. There was also significant closure of the ABGs across all frequencies in subsequent compared with the initial audiometric evaluation (ABG of 8.9± 3.7 in second compared to 12.9±4.1dBHL in initial assessment).
Table 2: Audiologic changes occurring in the course of treatment in 65 ears.
| Audiometric assessment | ||||
| Parameter | Initial | SecondStatistics | p-value | |
| Pure tone average, PTAv in dBHL | ||||
| Low frequency (0.25-1.0kHz) | 28.7 | 25.5 | 2.678 | 0.017 |
| High frequency (2.0-8.0 kHz) | 39.1 | 31.9 | 9.6578 | 0.011 |
| All frequencies (.25-8.0 kHz) | 33.9 ±7.4 | 27.1 ±6.6 | 12.471 | 0.001 |
| Air-bone gap, ABG in dBHL | ||||
| Low frequency (0.25-1.0kHz) | 15.7 | 10.9 | 10.328 | 0.001 |
| High frequency (2.0-4.0 kHz) | 10.1 | 8.3 | 2.591 | 0.021 |
| All frequencies (.25-4.0 kHz) | 12.9 ±4.1 | 8.9 ±3.7 | 10.687 | 0.010 |
The changes in hearing thresholds was compared between the low and high frequencies in the 65 ears with improved hearing in Table 3. There were significant changes in the audiometric parameters (i.e. improvement in hearing and ABG closure) occurring more at the low compared with the high frequency. The median PTAv was 7dBHL, while that of the ABG was 3.5dBHL. There were also significantly more improvements of PTAv>7dBHL and ABG closure of >3.5dBHL in the low compared with the high frequency.
Table 3: Changes occurring in hearing thresholds at different frequencies in 65 ears.
| Changes in Parameters | Low frequency | High frequency | Statistics | p-value |
| PTAv change | 8.7 ±3.9 | 7.2 ±4.4 | 3.265 | 0.002 |
| ABG change | 4.7 ±2.9 | 2.8 ±2.3 | 10.878 | <0.001 |
| PTAv >7dBHL | 47 (72.3%) | 31 (47.7%) | 5.801 | 0.016 |
| ABG > 3.5dBHL | 42 (64.4%) | 15 (23.0%) | 7.692 | 0.006 |
Discussion
It is expected that injuries of the extent that will perforate the tympanic membrane should cause some level of hearing impairment, at least transiently, but the changes that occurs afterwards may be more important. This has medical and legal implications on the subjects. The study has found significant hearing impairment in traumatized ears compared to their non-traumatized counterparts. The fact that most of the hearing impairments in the traumatized ears were of the conductive type was not surprising as the violation of the tympanic membrane should impair sound conduction through the middle into the inner ear. Conductive type of hearing loss occurring in the speech frequencies was previously reported as the most common form of hearing loss in patients with non-explosive blast injury to the ear in Nigeria7.
The hallmark of conductive hearing loss on audiometric assessment is an air-bone gap. Normally, the air-conduction thresholds are slightly better than those of the bone conduction, but the difference between these is often less than 5dB. However, in conductive hearing loss, the bone conduction is better than the air conduction creating a noticeable gap between the two audiometric tracings. An ABG of at least 10dBHL is assumed noteworthy8. Traumatized ears had significantly increased ABGs (average of 12.9dB) compared with their non-traumatized counterparts (average of 6.5dB) in this study.
On the contrary,Hempel JM et al9, reported bone conduction thresholds for traumatized ears were higher in low, middle, and high frequencies compared with the contralateral ears by trend which suggests SNHL. Some of our patients actually had sensorineural and others had combined conductive and sensorineural (mixed) hearing loss. This could connote factors other than disruption of sound conduction interplay in these patients. The direct effects of trauma on the inner ear hair cells with shearing forces affecting their actions, or a round window fistula in which a membrane ruptures between the inner and middle ear may explain the accompanying SNHL10. The extent of trauma to the ear can be qualified with proper hearing assessment. Thus it is imperative that audiometric assessments are performed in all forms and types of trauma to the ears. The SNHL noticed in the patients may also pre-date the traumatic event. This is instructive as up to 36.2% of the non-traumatized (contralateral) ears had SNHL. This might be from previous assaults especially noise induced hearing loss, which has be noted to be widespread in the environment11.
Hearing impairment is classified based on the extent or degree of hearing loss. Almost two thirds of the traumatized ears (64.4%) had mild form of hearing impairment. Hearing impairment of magnitude of at least 40dB (moderate hearing loss) will need some form of aid or assistance for hearing12. However even mild forms of hearing impairment can be associated with morbidities, and should be taken serious. Moreover, there is a tendency of progression with hearing loss worsening with time. Thus it is necessary to monitor hearing changes in patients with any degree of impairment.
Studies have shown that most of traumatic tympanic membrane perforations have good prognosis with spontaneous healing occurring within 3-12 weeks5,13. It was assumed reasonable to check the hearing thresholds to clarify changes within this period. Monitoring of the hearing thresholds in our patients revealed an improvement in the hearing six weeks post-injury. The improvement affected all the frequencies. This was also corroborated with closure of the ABGs across all the frequencies. Thus it was ascertained that significant improvement occurred in the hearing of the patients, similar to previous reports14.
Some patients hearing however did not improve while some (11.0%) of the traumatized ears had worsening of the hearing loss. Post traumatic hearing loss is a serious issue. Hearing assessments in such patients may require tests that are objective rather than the subjective PTA for clarification and better definition. This is against the background that some patients may malinger, feign or exaggerate hearing impairment for purposes of personal gain, or expectation of compensation during litigations. The tests that can be utilized in such cases include electrocochleography (ECOG), auditory brainstem audiometry (ABR), and otoacoustic emissions15.
Patients with hearing loss of moderate degree or above in the better ear will require some assistance the simplest of which is the hearing aid. Hearing aids have evolved over years from the crude form, through the analogue and presently sophisticated and sensitive digital hearing aids are being deployed16. There has also been accompanying upgrading from the obviously bourgeois body-worn to the relatively hidden, completely hidden to osteo-integrated hearing aids17. Definitely some of our patients will require hearing aids. The major drawbacks of hearing aids however remain high cost and relative non-affordability, dearth of competent clinical audiologists with the requisite technicalities for its fixing and maintenance. Other devices like the cochlear implants are bedeviled with similar problems. Thus patients are often left for the attending clinician to manage hearing impairment and its attendant co-morbidities.
Clinicians are particularly interested in patients’ communication which is related to hearing at the speech frequency levels. Few studies7, 18 on such hearing changes and dynamics have noted that hearing impairment and accompanying changes were frequency specific. We performed the hearing dynamics between two (low and high) frequency ranges. Initial audiometric assessments in our patients revealed comparatively higher hearing thresholds in the high frequencies and higher ABGs in the low frequencies. The differences in these parameters were not statistically significant between the frequencies. It has been noted that ABGs were largest at the lower frequencies and decreased as frequency increased18. We also noted that improvements in hearing occurred significantly more at the low, compared with the high frequencies. It has however been reported that high frequency hearing loss, among other symptoms was associated with good prognosis in TTMP9.
A study on blast injury of the ears in Southern Thailand noted that residual hearing loss after 3 months of trauma to the ears was rather mild and occurred at the high frequencies19. Nageris et al20, however reported that cochlear hearing loss, in most cases did not improve even one year post-injury. In this study there was an improvement in the hearing in 89.0% of the traumatized ears. This improvement was appreciable compared with the rate of 77% improvement in PTAvs reported earlier in cases without surgical intervention14. This reinforces the assertion that cases of traumatic injuries to the tympanic membrane heal well and have relatively good restoration of hearing with or without surgical intervention14. It appears the most important principles still remain prevention of infection in the traumatized ears, and stimulation of healing.
Some limitations were noted in this study. The subjectivity of PTA as a hearing investigative tool is acknowledged as a limitation. Moreover, data for some of the patients were excluded because they gave inconsistent and unreliable responses in the course of audiometric assessments. Similarly the lack of uniformity in the timing of the audiometries may create disparities in the comparisons that were made considering the temporal changes in the hearing.
Conclusions
In conclusion, patients with traumatic tympanic membrane perforation majorly had conductive hearing loss in the injured ears with audiometric confirmed air-bone gaps and increased hearing thresholds which were not frequency dependent. There was appreciable improvement in hearing parameters over time, significantly more at the low frequencies.
Footnotes
Competing Interests: The authors have declared that no competing interests exist.
Grant support: None
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