Size of Tympanic Membrane Perforation and Hearing Loss

Transcription

1 J Nep Med Assoc 2006; 45: Size of Tympanic Membrane Perforation and Hearing Loss Bhusal C L *, Guragain R P S *, Shrivastav R P * * Tribhuvan University, Institute of Medicine, Maharajgunj, Kathmandu, Nepal abstract This prospective study was done to assess the level of preoperative hearing impairment in different sizes of pars tensa perforation in patients with chronic suppurative otitis media (CSOM) tubotympanic type undergoing myringoplasty. A total of 50 patients were recruited from the outpatient Department of Otorhinolaryngology - Head and Neck Surgery from June 2003 to May Cases of CSOM tubo-tympanic type with dry central perforation, conductive type of hearing loss were subjected to myringoplasty. Preoperative audiometric evaluations were done. While operating under microscope diameter of perforations were measured and perforations were grouped according to the size. It was observed that greater hearing loss was reported in group D perforation (44dB), where as in group A, it was 31 dbhl. The average hearing loss at 500Hz was 46.40dB, at 1000Hz was db and at 2000Hz it was 31.9 db. This shows that the hearing loss is more at lower frequencies and less as the frequencies increase. This study shows that as the size of perforation is increased, the hearing loss also increases. The hearing loss is more marked at lower frequencies as compared to higher frequencies. Key Words: Hearing loss, Myringoplasty, Tympanic membrane perforation. Introduction Chronic suppurative otitis media (CSOM) is one of the most common ear diseases in developing countries. Ear diseases are quite common and important causes of the hearing disability in Nepal. CSOM is defined as a persistent disease, insidious in onset, often capable of causing severe destruction of middle ear structure with irreversible sequale, which is clinically manifested with deafness and discharge for more than three months. 1 The prevalence of deafness and ear disease surveyed in six districts in Nepal, revealed that prevalence of deafness was 16.6% of the Address for correspondence : Dr. Chop Lal Bhusal Tribhuvan University, Institute of Medicine, Maharajgunj, Kathmandu, Nepal. pbhusal@ntc.net.np Received Date : 14 th Nov, 2005 Accepted Date : 19 th Mar, 2006

2 Bhusal et al. Size of Tympanic Membrane Perforation and Hearing Loss 168 general population in age group of 5 years and above. Of people examined in the survey, 7.2% were found to have CSOM of tubo-tympanic type and 0.9% atticoantral type. It also showed that about one-third of the preventable deafness was due to CSOM. 2 solely the result of a perforation or if additional pathologies are involved. Therefore, the present study is an attempt to co-relate the size of perforation and the hearing loss. Materials and Methods Perforation of the tympanic membrane (TM) can result from trauma middle-ear disease, or the treatment of middle-ear diseases. Perforation occur as a result of the disease process in chronic otitis media, which affects at least 0.5% of the population. 3 CSOM can lead to conductive hearing loss up to 60 db, which constitutes a serious handicap. 4 In an audiometric study of perforations due to ear disease, Anthony and Harrison confirmed the importance of area and location of the perforation in determining the degree of hearing loss. However, they restricted their analysis to only those cases in which the air-bone gap was closed by myringoplasty. They also concluded that a useful formula for prediction of hearing loss on the basis of size and location of perforation is impossible because of wide variations in individual cases within any particular group. 5 Ahmad and Ramani studied TM perforations in young, otherwise healthy adult males who had been referred for closure of perforations which had resulted from trauma or infection. These authors examined affected ears under the operating microscope and measured its area with techniques more sophisticated than those that had been used hitherto. 6 When the vibrating surface area of the tympanic membrane is decreased, there will be reduced amplification of the sound. The hearing loss will be proportional to the size of the perforation. 7 The larger the size of the perforation, greater is the amount of the sound waves, which pass through it leading to the nullifying effect. The effects of TM perforation on middle-ear sound transmission are not well characterized, largely because ears with perforation typically have additional pathological changes. 8 A better description of perforation effects on middle-ear function is needed so that clinicians know what magnitude and frequency of hearing loss to expect with perforations of various sizes. With such information, clinicians will be able to predict whether hearing loss is This prospective, observational study was conducted among a purposive sample of first 50 consecutive patients who underwent myringoplasty in the Department of Otorhinolarygology - Head and Neck Surgery, Tribhuvan University Teaching Hospital, Kathmandu, Nepal form June 2003 to May Patients of both sexes who had dry ear and who gave the consent to participate in this study were included. Patients below 14 year of age, and with active disease, tympanosclerosis, revision myringoplasty, mixed or sensory neural hearing loss (SNHL), CSOM attico-antral type, ossicular chain fixation or disruption and patients in whom ossicular chain status could not be assessed were excluded from this study. The pre-operative examination included history taking, and examination of the ears under microscope (EUM). Audiometric assessment was performed using a clinical audiometer calibrated according to ISO standard in a sound treated room. A pure tone audiometry within one week prior to surgery was done at the frequencies of 250, 500, 1000, 2000, 4000 and 8000 Hz. Air and bone conduction threshold were determined with appropriate masking technique whenever indicated. Hearing level was defined as the mean air conduction threshold at 500, 1000 and 2000 Hz and average of these frequencies were calculated to measure the hearing level. Pre-operative examination findings were reconfirmed by EUM during surgery. EUM and per-operative findings were recorded on a performa. The diameters of the perforations were measured under microscope by placing over them a thin metallic rod of lengths ranging from 4 mm to 10 mm, graduated in ½ mm. steps. The surface area of the perforations were calculated by using a mathematical formula, A =π bc/4, where A= area of perforation, b= length of the minor axis, and c= length of the major axis.

3 169 Bhusal et al. Size of Tympanic Membrane Perforation and Hearing The patients were divided in the following four groups depending on percentage of area involved as suggested by Ahmed et.al. 6 A - 10 percent of TM surface area. B - between 10 percent and 20 percent of TM surface area. C - between 20 percent and 40 percent of TM surface area. D - above 40 percent of TM surface area. under local anesthesia, using 2% xylocaine with 1:100,000 adrenaline. Data processing and analysis were done by using computer software SPSS and f-test, t-test and x 2 -test were applied wherever necessary. p values of <0.05 were considered to be statistically significant. Results The average surface area of an intact TM was taken as 64.3sq. mm. 7 A total of 50 patients were enrolled in this study. The result of the study is shown in the following tables and figures. Myringoplasty was performed through transcanal route, but if patient had with a narrow ear canal, or if the anterior rim of the drum was obscured by a prominent bony over hang, a post-aural route was preferred which enhanced the exposure in such circumstances. It was carried out Age and Sex Distribution Table I shows the distribution of patients according to the age and sex. Majority of patients 35 (70%) were in the years age group with 16 (32%) males and 19 (38%) females. Table I : Age and Sex Distribution (n=50) Table II : Chief Complaints (n=50) Table III : Size of perforation (n=50)

4 Bhusal et al. Size of Tympanic Membrane Perforation and Hearing Loss 170 Table IV : Size of Perforation and Hearing Loss (n=50) * chi-square test SD = Standard Deviation Figure 1 : Size of Perforation and Hearing Loss (n=50)

5 171 Bhusal et al. Size of Tympanic Membrane Perforation and Hearing Chief Complaints All the patients complained of intermittent otorrhoea and hearing loss. Only 10(20%) of them complained of tinnitus in the affected ears. Frequency of various sizes of perforation Majority of the patients were of group-d (19/50), i.e. above 40% of perforation of TM, followed by group-b (13/50), ranging from percentage of perforation of tympanic membrane. Size of Perforation and Hearing Loss Maximum hearing loss of 43.8dB was observed in group D perforations, where as 30.8 db was observed in group A perforations. Irrespective of the group, the greater hearing loss was observed in 500 Hz and less in 2000Hz frequency. Discussion Patients below 14 years of age were excluded because all myringoplasty was done under local anaesthesia, which is difficult to perform in this age group. Similarly, patients above 45 years of age were excluded because, such patients may have presbyacusis. For calculation of average hearing loss (air conduction threshold) three speech frequencies namely 500Hz, 1000Hz and 2000Hz were selected. Puretone threshold audiometry has become the standard behavioral procedure for describing audiometry sensitivity; therefore, pure tone audiometry had been used for assessment of hearing level in this study. In this study the most commonly affected age group was years with 35 (70%) patients. The reason could be that this age group is socially active and health conscious. The findings of this study are similar to that of Prasansuk et.al, who studied 30 ears of 15 patients aged between years of age. 9 As our results suggest (Fig. 1), as the size of the perforation increased, the curve of hearing loss moved up ward. The data indicate a direct relationship between the size of perforation and the degree of hearing loss observed. Maximum hearing loss (43.8 db) was observed in group D perforation and minimum (30.8dB) in group A. Similar findings were reported by Ahmad and Ramani. 6 A hearing loss of 30dB in group D and 8dB in group A was reported in their study. Austin 11 also found similar findings. He stated that the hearing loss is least in group A and steadily increases to a maximum in group D. Many studies of perforations both in animals and human studies reveal a direct correlation between the size of the perforation and the hearing loss. 5,6,12,13 Our study also confirm the above mention findings that the size of the perforation has a major role on hearing loss. Many more studies with larger number of cases are required to co-relate the pre-operative hearing loss and the size of TM perforation, so that the study can conclude anything correctly. Conclusion This study attempts to correlate the degree of hearing loss to different sizes of perforation. In the present study it has been shown that the hearing loss increases as the size of the perforation increases. Group D perforation (perforation size more than 40%) causes more hearing loss than group A (perforation sizes 0-10%). Hence hearing is least affected in group A and steadily increased to a maximum in group D. Clinically, it may be possible to predict the amount of hearing loss based on size of the tympanic membrane perforations. This study consists of 25 males and 25 female patients, the ratio being 1:1. A similar M:F ratio of 1:1 is reported by Yong. 10

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