A Hospital based study on sudden sensorineural Hearing Loss: It’s audiological characteristics and prevalence

Objectives: To analyze the prevalence & characteristics of sudden sensorineural hearing loss. Methods: This cross sectional study including n=377 cases of sensorineural hearing impairment, using non-probability convenience sampling, who fulfilled the selection criteria was conducted from 1st July 2019 to 31st October 2019. Study was conducted at Audiology section of ENT department, Lahore General Hospital, Pakistan. Sample included both genders, aged 17-70 years. Cases suffering from inflammatory or obstructive conditions of the external or middle ear and those who could not undergo pure tone audiometry were excluded from the study. Following consent for inclusion in study, data was collected using basic demographic and medical history sheet followed by Audiometric evaluation. Statistical Software for Social Sciences Version 20.0 was used for data analysis. Results: The prevalence rate of sudden sensorineural hearing loss of 14(3.7%) being significantly more common in males 11(78%) than females 3(22%) (p=0.05) & age group 15-35 years (p=0.001). It is commonly of severe or profound degree with downward sloping audiogram (p<0.05), however it is not associated with vertigo (p=0.32), tinnitus (p=0.08) with no side predilection (p=0.27). Conclusion: We conclude that the prevalence of SSNHL is 3.7% being significantly more prevalent in males and those aged15-25 years. It is mostly characterized by severe to profound degree of hearing loss with downward sloping audiogram with no associated vertigo, tinnitus and side predilection.


INTRODUCTION
Sudden sensorineural hearing loss (SSNHL) is considered a medical emergency 1 and is defined as Sensorineural Hearing loss (SNHL) of > 30db on three contiguous pure tone audiometric frequencies within 72 hours. 2 SSNHL is relatively common complaint and of idiopathic origin in 90%, other etiologies being infection, ototoxicity, noise, trauma, autoimmune disease, malignancy, vascular, neurologic, metabolic, and even nonorganic etiology. 3 The exact incidence of Sudden SNHL is not known. Estimate of incidence show a wide range of 11-77 per 100,000 people per year, 4 with equal gender distribution and can occur at any age. 5 SSNHL can present with varying degree of hearing loss and can accompany tinnitus and vertigo. 5 Majority of cases are idiopathic with unknown etiology. 2,6 Risk factors are uncertain and Herpes Simplex type 1 viral infection has been implicated. 7 SSNHL is a subjective symptom perceived by the patient and hence to determine prevalence of hearing loss (HL), its type and threshold of hearing, a pure-tone audiogram is required. 3 Though majority (65%) cases of idiopathic SSNHL recover spontaneously, 8 however cases need to be investigated for infective causes and to exclude lesions in cerebellopontine angle, internal auditory canal and inner ear. 8 Early recognition and intervention can help recovery in thresholds of hearing, 6 which depends on severity of HL, age, presence of vertigo and configuration of audiogram. 2 Institution of early treatment with standard doses of oral steroids in cases with idiopathic SSNHL is recommended 8 and may increase changes of recovery.
Acknowledging the available literature, the exact prevalence of SSNHL is not known with highly variable incidence reported in studies, 4 with no local literature on its prevalence and characteristics. Hence the current study was conducted to explore the prevalence & characteristics of sudden sensorineural hearing loss. This study has significant importance as its finding may be helpful for researchers to conduct in depth research in the field with different objectives. SSNHL is topic of great importance and needs more research to be conducted in Pakistan.

METHODS
This is a cross sectional study which recruited n=377 patients with SNHL, who attended Audiology section of ENT Department of Lahore General Hospital, Pakistan using non probability convenience sampling technique over a period of four months extending from 1st July 2019 to 31st October 2019. Sample included both genders, aged 17-70 years. Cases with inflammatory and obstructive pathologies of external and middle ear, those who could not undergo audiological testing or were found to have conductive element were excluded. Study was conducted after obtaining approval of IRB of Isra Institute of Rehabilitation Sciences, Isra University vide Registration No. 1609-M.Phil HS-007 dated 24 th June, 2019 and informed consent of the sample. A basic demographic sheet, medical history sheet and PTA were used to collect data.
History was noted in a confidential setting including duration of HL, associated complications like tinnitus, vertigo, exposure to ototoxic agents, occupational or leisure noise and treatment history. This was followed by physical examination including otoscopy to rule out any obstructive and inflammatory pathology and pure tone audiometry was done in cases suspected of having sensory neural hearing loss. Computer based Pure Tone Audiometer Labat, made in Italy was used and testing performed in sound proof room which met American National Standards Institute (ANSI) S 3.1-1991 standards. Both ears will be tested for air and bone conduction using the method of ascending pure tones at frequencies of 0.5, 1, 2, 4, 6 and 8 kHz before descending to 1 and 0.5 kHz. Bone conduction was checked at frequencies of 0.5 to 4 kHz.
Data collected was analyzed using SPSS -Version 20.0. Descriptive statistics was used. Variables specially studied included degree and type of HL, ears affected, associated symptoms and age and gender. Pearson's Chi-square test was used to determine association of type of HL with demographic and clinical variables. Independent sample t-test was used to see any significant difference in mean thresholds between the two ears. P-value of 0.05 was taken as significant.
No significant association (p=0.32) of vertigo was noted with no case of vertigo among cases of SSHL. Similarly no significant association (P=0.081) of tinnitus was noted with eight out of 14 cases of SSNHL having tinnitus and 125 out of 363 cases of chronic hearing loss with tinnitus.
There was significant association (p=0.032) of severity of hearing loss in the right ear with maximum (n=8) cases having profound and n=4 having severe hearing loss among cases with SSNHL. On the other hand in the Left ear majority (n=6) had severe HL while n=5 had normal hearing in the group with SSNHL. While in the chronic HL cases majority (n=111) had profound HL. The difference was significant (p<0.001).
No significant difference (p-0.27) was noted as regards side affected in SSNHL and chronic HL groups. As regards threshold of hearing in cases with SSNHL study revealed a continuous rise from a Mean threshold of 54.28 ± 28.22 at 250 Hz to 72.89 ± 31.04 at 8 KHz in the Right Ear and from 54.88 ± 28.62 at 250 Hz to 75.46 ± 30.78 at 8 KHz in the Left Ear. However, t-test statistics did not reveal any significant difference at all the frequencies form 250-to 8 kHz (Table-I).

DISCUSSION
Sudden sensorineural hearing loss, recovers spontaneously in majority, hence exact incidence is not known with a wide range of 11 to 77 per 100,000 people affected per year. 4 In the current study with a sample population of 377 cases, a low prevalence of SSNHL of 14(3.71%) was found. In contrast in an American study, a high incidence of 27 per 100000 annually have been reported by Alexander & Harris. 4 The probable reason of low prevalence might be that majority of those affected delay consultation with a professional and hence recover and or don't give much importance to HL, which is evident from the attitude of our population in which even cases of oral cancer present delay reporting for a medical advice ranging from one month to two years. 9 In the current study of the 89 cases with unilateral HL, 5 had SSNHL, while of the 288 cases with bilateral HL 9 had SSNHL, however the difference was not statistically significant (p-0.27). In contrast to our study in which majority had bilateral HL, in a study by Atay G et al. in 45.9% cases right ear was affected and in 54.1% left ear was affected. 10 Present research revealed that SSNHL is more prevalent in males as compared to females. With a total population of 203 (53.8%) males and 174(46.2%) females, 11 males and Erum Naz et al. In the present study, SSNHL was significantly (p=0.001) more common in age group 15-35 years with 12 cases, while remaining two cases belonged to 36-55 years age group. In contrast Alexander and Harris, reported a higher incidence of 77/ 100000 cases at age 65 and above compared to 11/100000 below 18 years of age. 4 Similarly higher prevalence in 43-53 years age group has been reported by Trevino Gonzalez JL et al, 5 and by Lee HS et al. in 5th and 6th decade. 11 The higher prevalence in younger age group in our study might be due to the fact that reduced hearing in elder adults in Pakistani community is considered a norm especially in the rural areas and are not commonly brought to hospital.
As regards etiology, different studies have reported widely varying prevalence of different etiological causes. According to Lloyd SKW et al. in 30% cases of SSNHL cause is identified including infection (44%), otologic disease (17%), neurologic and vascular (12%), malignancies (7%) and miscellaneous (4%), while the remaining 70% cases are idiopathic. 6 In contrast majority (94.5%) of cases were idiopathic and in only 5.5% etiology was identified including acoustic neuroma, hemorrhage, inner ear malformations, and perilymph fistula in another study. 10 In the current study, in majority (71.43%) cases cause was identified while in the remaining it was considered idiopathic. Also in majority the cause was trauma due to road traffic accident and fall from bike. In a meta-analysis by Chau et al. reported infections in 13%, aural causes in 5%, trauma in 4%, Vascular in 3%, tumors in 2% and other causes in another 2%. 12 An interesting finding noted by Yen YC et al. was a threefold higher incidence in chronic otitis media cases. 13 Also a higher incidence (1.3 fold) of SSNHL has also been reported in cases with cardiac rhythm disorders, 14 Diabetes Mellitus, 15 and hypo and hyperthyroidism. 16 Here it must be kept in mind that identification of etiology is also related to the investigative facilities available and being used, which might result in difference in the frequency of different etiologies being reported from different centers.
In the present study there was significant association (p=0.032) of severity of hearing loss with type of HL with majority (eight cases) having profound SSNHL followed by ( 10 Common associated symptoms include aural fullness, vertigo and tinnitus. 6 However, no significant association (p=0.32) of vertigo was noted with no case of vertigo among cases of SSNHL in current study. Also no significant association (p=0.081) of tinnitus was noted with 8 out of 14 cases of SSNHL having tinnitus and 125 out of 363 cases of chronic hearing loss having tinnitus. In contrast international literature indicates association of symptoms of tinnitus as well as vertigo with a high frequency. 2 While vertigo did not significantly correlate with (p=0.219), while tinnitus was significantly correlated with hearing recovery (p=0.005), low initial threshold of hearing (0.002), down sloping graph (0.029) were positively associated with recovery. 17 According to Atay G et al. early initiation of treatment within five days (p<0.05) and flat audiogram in mid frequencies (p<0.05) show better prognosis 10 and vestibular system disorder is associated with worse outcome. 18 In SSNHL where cause is not found, therapy including steroids and antivirals have been found of benefit. 1,19 Novel approaches like neurorehabilitation using constraint-induced sound therapy has been recommended being safe and effective. 20