|Year : 2016 | Volume
| Issue : 4 | Page : 262-267
Unilateral sensorineural hearing loss: A retrospective study
Divyank Bansal, Saurabh Varshney, Manu Malhotra, Poonam Joshi, Narendra Kumar
Department of ENT and Head Neck Surgery, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India
|Date of Web Publication||13-Oct-2016|
Department of ENT, All India Institute of Medical Sciences, Rishikesh - 249 201 Uttarakhand
Source of Support: None, Conflict of Interest: None
Background: This retrospective study was carried out to know the characteristics of patients suffering from unilateral sensorineural hearing loss (USNHL) (type and degree). Aims and Objectives: (1) To know the incidence of pure USNHL (other ear being normal) in patients complaining of HL. (2) To establish the type and degree of USNHL in patients. Materials and Methods: This study was conducted over a period of more than 1 year to find out the pattern of pure USNHL (other ear being normal) in the patients attending ear, nose, and throat outpatient department (OPD) with a complaint of HL. Pure tone audiometry data of 1800 cases between August 2014 and December 2015 with HL were analyzed for this study. Demographic characteristics were compared with types and degrees of unilateral sensorineural hearing impairment. Results: A total of 1800 OPD patients who had a complaint of HL and had undergone pure tone audigram (PTA) in a period of more than 1 year in the Department of Otorhinolaryngology and Head and Neck Surgery were studied. SNHL type was the highest with 802 cases (44.55%). Out of 802 cases of SNHL, 257 (32.05%) were USNHL - out of which, only 155 patients (60.31%) had pure USNHL with other ear being normal; this constituted the study group, i.e., 155 patients (8.6%) out of 1800. Age of patients ranged from 9 years to 76 years (mean age - 41.5 years). Male:female ratio was 1.31:1. Both ears were almost equally involved. The highest numbers of USNHL patients were seen in the age group of 31-40 years (23.87%). Most cases presented with mild (34.2%), followed by profound (31.6%) USNHL. Conclusion: Our study concluded that SNHL type is the most common type (44.55%) of hearing impairment among patients complaining of HL. The incidence of pure USNHL (i.e. other ear being normal) was 60.31% (155/257) cases of USNHL, 19.32% (155/802) cases of SNHL, and 8.6% (155/1800) cases of PTA performed on patients complaining of HL. Limited work has been published on incidence, characteristics, and causes of pure USNHL. Further studies and researches are required in the field of USNHL to know the incidence, functional and psychological impact, and treatment options.
Keywords: Contralateral routing of signals, PTA, Sensorineural hearing loss, Unilateral
|How to cite this article:|
Bansal D, Varshney S, Malhotra M, Joshi P, Kumar N. Unilateral sensorineural hearing loss: A retrospective study. Indian J Otol 2016;22:262-7
| Introduction|| |
Hearing impairment cannot be seen, and hence, its effects are not visible to others, so deaf suffers in silence. Unlike blindness, deafness often provokes ridicules rather than sympathy.  Imagine pressing your ear with one hand and trying to hear with the other. In unilateral sensorineural HL (USNHL), HL is present only in one ear. The other ear will have normal hearing capacity. It can be just a mild HL that does not affect daily functioning, or it can be a very major loss with a severe or profound intensity, causing hearing handicap. When a patient can hear from only one ear, and there are limited possibilities to compensate for the handicap, for example, changing the listening position, group discussions, and dynamic listening situations become difficult. Individuals with profound unilateral HL are often perceived as socially awkward due to constant attempts to maximize hearing, leading to socially unique body language and mannerisms.  Unilateral HL is found to be occurring in both children and adults. People with unilateral HL are found to have difficulty in distinguishing sound and speech from the background noise.
Incidence of unilateral sensorineural hearing loss
HL is an extremely common disorder, but there are very few studies on incidence and characteristics of USNHL.
With approximately 32 million Americans having some degree of hearing impairment, SNHL accounts for 90% of the cases. The vast majority of patients with SNHL have bilateral HL. In the United States, approximately 60,000 new cases of USNHL occur annually (www.singlesideddeafness.com) and far more occur internationally. 
In India, a retrospective study was done on audiometric data of 252 patients to know the demographic characteristics of patients suffering from HL - 163 (66.5%) had SNHL, out of which only 6 cases (3.7%) had USNHL.  In another Indian study on 820 patients diagnosed with pure SNHL on pure tone audiometry, 675 (82.3%) had bilateral involvement and USNHL was in 145 (17.6%) patients. Among unilateral cases, the right ear involvement was in 48.2% cases and the left ear involvement was in 51.8%. 
Causes of unilateral hearing loss
HL can occur suddenly, wiping out hearing within 72 h (sudden SNHL [SSNHL]), and it can affect anyone of any age. Interestingly, most cases of sudden-onset HL are single-sided. USNHL, affecting both the nerves and the inner ear, is irreversible.
It is difficult to find out the root cause for the occurrence of unilateral HL in a particular case. However, the general causes for the occurrence can be classified as detailed below.
- Trauma to the ear or parts of the ear
- Exposure of the ear to excessive and continuous noise
- Genetic HL
- Infections and illnesses of various types.
Numerous disease processes can lead to severe-to-profound USNHL. These include congenital, SSNHL; idiopathic SNHL; neoplasms; vestibular schwannoma (acoustic neuroma); demyelinating pathologies such as multiple sclerosis, vertebrobasilar arterial occlusion (stroke), acoustic trauma, head injury, perilymphatic fistula, ototoxic drugs, labyrinthitis, and Meniere's disease; and autoimmune disease (Cogan disease, Wegener's granulomatosis, lupus, Takayasu arteritis, systemic sclerosis, and other rheumatological disorders). 
What happens in unilateral sensorineural hearing loss
Our physiology is designed for bilateral hearing, ears located on either side of the head. This design, with a space between the two ears, has several evolutionary benefits. The handicap experienced by adults with bilateral SNHL is well known, but the consequences of USNHL are often underestimated based on the assumption that a person with normal hearing in the contralateral ear is not likely to face a major handicap. 
When we hear a sound, the nerves of the ear closer to the sound get stimulated just a little earlier than the ear on the other side. However, just a microsecond of difference, it helps the ear to determine which side the sound is coming from. This advantage gets even more pronounced with localization of hearing which helps us discriminate between sounds coming from a distance and sounds close by. The stereo sound effect, letting us hear sounds coming from 360°, gives that rich full sound we are used to hear. Binaural hearing is vital for sound localization, speech discrimination in a background of noise, ability to identify common sounds, and ease of listening. When these sensitive functionings get thrown off-radar, normal life can get quite confusing. For example, the person may not be able to understand normal speech, direction of a sound, or from how far the sound is coming. This can either cause accidents or hamper movement in regular life, while crossing roads, at home or in the workplace. With speech and background noise presented at the same level, persons with unilateral deafness were found to hear only about 30-35% of the conversation. 
| Materials and Methods|| |
This is a retrospective study on the pure tone audiometric (PTA) data of 1800 patients, irrespective of age and sex from August 2014 to December 2015, who visited the outpatient department (OPD) of Otorhinolaryngology and Head and Neck Surgery, with a complaint of HL. Based on PTA, the types of hearing impairment were categorized as conductive/sensorineural/mixed and unilateral/bilateral.
Pure tone audiogram (PTA) records of 1800 patients who had complained of hearing impairment were analyzed to know the incidence of pure USNHL (study group) - excluding the cases of mixed HL. This group of USNHL was studied further for demography, type, laterality, and severity of HL with the aims and objectives to:
- Know the incidence of USNHL in patients complaining of HL
- Establish the type and degree of USNHL in patients.
- Patients with USNHL (other ear being normal) based on PTA irrespective of age and sex
- Individuals without any previous history of ear discharge and normal tympanic membrane on otoscopy.
- Patients with conductive HL, mixed HL, and bilateral SNHL
- USNHL with other ear not being normal (i.e., having conductive/mixed HL)
- Operated patients.
A total of 1800 OPD patients who had complaints of HL and had undergone PTA in a period of more than 1 year in the Department of Otorhinolaryngology and Head and Neck Surgery were studied. SNHL type was the highest with 802 cases (44.55%). 194 cases (10.77%) had normal hearing.
Incidence of pure unilateral sensorineural hearing loss
Out of total 1800 PTA for HL, 802 (44.55%) had SNHL (bilateral - 545 [67.95%]; unilateral - 257 [32.04%]) which was the most common type of hearing impairment among patients complaining of HL. Out of 802 cases of SNHL, 257 (32.05%) had USNHL - out of which, only 155 patients (155/257) (60.31%) had pure USNHL with other ear being normal; this constituted the study group, i.e., 155 patients (8.6%) of 1800 PTA done for HL and 155/802 cases of SNHL (19.32%) [Figure 1] and [Table 1].
|Table 1: Comparison of gender - wise distribution of various types of hearing impairment|
Click here to view
Out of 1800 PTAs evaluated, 58.39% were males and 41.61% were females [Table 1].
In our study group of 155 pure USNHL cases, 88 (56.77%) were males and 67 (43.23%) were females. Age of patients ranged from 9 years to 76 years (mean age - 41.5 years), maximum patients were in 3 rd decade (23.87%), followed by 2 nd (21.29%) and 4 th decade (21.29%) [Table 2].
Out of 155 patients, 74 patients (47.7%) had their right ear involved and 81 patients (52.3%) had their left ear involved [Table 2].
Twelve cases (7.74%) had sudden onset of USNHL (SSNHL) while 143 (92.26%) had gradual onset.
Severity of sensorineural hearing loss
Severity of USNHL ranged from mild (34.2%) to profound (31.96%) (right ear - 25 patients [33.8%] had mild HL and 20 patients [27%] had profound HL; left ear - 28 patients [34.5%] had mild HL and 29 patients [35.8%] had profound HL). Out of 12 cases who had SSNHL, 8 (66.67%) presented with profound SNHL, 3 (25%) with severe, and 1 (8.33%) with moderate to severe SNHL [Table 3].
| Discussion|| |
Hearing impairment is one of the most prevalent chronic conditions after hypertension and arthritis. Over 5% of the world's population - 360 million people - have disabling HL (328 million adults and 32 million children).  The incidence of bilateral SNHL ranges from 1.4 to 3 per thousand live births in various studies worldwide. Of the SNHL described in children, 50% is thought to be genetic, 25% acquired, and 25% unknown etiology.
Limited studies on incidence of USNHL are available in the literature. In an Indian retrospective study done on audiometric data of 252 patients to know the demographic characteristics of the patients suffering from HL - 163 (66.5%) had SNHL, out of which only 6 cases (3.7%) had USNHL.  In another Indian study on 820 patients diagnosed with pure SNHL on pure tone audiometry, 675 (82.3%) had bilateral involvement and USNHL was in 145 (17.6%) patients.  In our study, out of 1800 cases, 802 (44.55%) had SNHL (bilateral - 545 [67.95%]; unilateral - 257 [32.04%]) which was the most common type of hearing impairment among patients complaining of HL. Out of 257/802 (32.05%) cases of USNHL - only 155 patients (155/257) (60.31%) had pure USNHL, with other ear being normal; this constituted the study group, i.e.,155 patients (8.6%) out of 1800 PTA done for HL and 155/802 cases of SNHL (19.32%). Hence, our study had incidence of pure USNHL in 19.32% cases of SNHL, which is higher than other studies. Our higher incidence may be because of difference between the total populations being considered; we have taken only patients attending ear, nose, and throat OPD.
In our study of 155 USNHL cases, 88 (56.77%) were males and 67 (43.23%) were females, which is in agreement with the WHO Deafness and HL Fact Sheet No. 300 (2015), which states that males were more affected by SNHL and mixed and conductive types of HL. Age of patients ranged from 9 years to 76 years (mean age - 41.5 years), maximum patients were in 3 rd decade (23.87%), followed by 2 nd (21.29%) and 4 th decade (21.29%). The least number of cases was in the age groups of 71-80 years (0.64%), followed by 1-10 years (1.29%). Bilateral SNHL impairment was more than unilateral (bilateral - 545 [67.95%]; unilateral - 257 [32.04%]).
Sharma et al. among pure unilateral cases reported right ear involvement in 48.2% of cases and left ear involvement in 51.8% of cases,  which is in alignment to our study in which 74 patients (47.7%) had their right ear involvement and 81 patients (52.3%) had their left ear involvement, which is also consistent with the findings of Brookhouser et al., who in their study of 324 children and adolescents with USNHL at the Boys Town Research Hospital found that the left ear was affected in 52% and the right ear in 48%. 
In our study of 155 cases, only 12 cases (7.74%) had sudden onset of USNHL (SSNHL) while 143 (92.26%) had gradual onset. In a study of 820 patients of SNHL (2015), 42 (5%) presented with sudden HL and 778 (95%) with gradual HL,  in contrast to Hughes et al., who, according to their study, labeled that among all cases of SNHL in the United States, approximately 1% of cases are of SSNHL. 
In our study of USNHL, most of the patients across the spectrum of severity of HL presented to the hospital when their HL ranged from mild (34.2%) to profound (31.96%) (right ear - 25 patients [33.8%] had mild HL and 20 patients [27%] had profound HL; left ear - 28 patients [34.5%] had mild HL and 29 patients [35.8%] had profound HL). This indicates that even the mild HL is noticed by most of the patients because it causes them significant problems in their daily activities. Out of 12 cases who had SSNHL, 8 (66.67%) presented with profound SNHL, 3 (25%) with severe, and 1 (8.33%) with moderate to severe SNHL.
Usually, it is felt that patients with severe-to-profound USNHL function normally. It is now well established, however, that USNHL is a handicap that can negatively impact quality of life.  A study of USNHL among Indian patients showed mild to moderate psychosocial handicap using the Hearing Handicap Inventory for Adults in about one-third of patients and no handicap in a little over half the patients. Sound localization and speech in noise are significantly affected in these patients. However, despite this, most patients do not choose to go in for any kind of rehabilitative device and present to the physician to be reassured that there is nothing sinister about their problem. 
USNHL is known to cause: 
- Body language and mannerisms which appear socially awkward or unusual
- Frequent headaches, stress
- Social isolation
- Chronic interpersonal communication difficulties due to inability of brain to isolate or beam form sounds and voices of other individuals
- Appearance of anxiousness even in low-noise situations
- Trouble figuring out where sounds are coming from
- Trouble paying attention to what people are saying: "Evasive" behavior misdiagnoses as attention deficit hyperactivity disorder
- Seeming lack of awareness of other people's personal space and moods since brain is hyperfocused on deciphering auditory information in lieu of nonverbal social cues
- Lack of sound depth: Any background noise (in the room, in the car) is flat and wrongly interpreted by the brain. The effect is similar to what happens when trying to hear someone speaking in a noisy crowd on a mono-TV. The effect is also similar to talking on the phone to someone who is in a noisy environment
- Inability to filter out background noise or selectively listen to only the important portion of the noise in the environment
- For SNHL, the lack of input coming from the damaged sensory apparatus can cause "ghost beeps" or ringing/tinnitus as the brain attempts to interpret the now missing sensory data. The frequency and the volume of the noise can increase according to one's physical condition (stress, fatigue, etc.). This can aggravate social problems and increase the difficulty of speech comprehension
- Talking loudly or "broadcasting:" The affected person cannot perceive the volume of his or her voice relative to other people in the same room or close company, resulting in being characterized by others (who may be located beyond normal auditory range) as domineering or boorish.
Learning of the central nervous system by "plasticity" or biological maturation over time does not improve the performance of monaural listening.  In case where surgical remedy has been ruled out by an otolaryngologist, then the following types of amplification of sound signals are the probable method of the treatment.
Contralateral routing of signals hearing aids
Hearing aids take sound from the ear with poorer hearing and transmit to the ear with better hearing [Table 4].
|Table 4: Types of contralateral routing of signals (CROS) hearing aids[13,14]|
Click here to view
There have been very few studies comparing CROS systems. One study of the BAHA system showed a benefit depending on the patient's transcranial attenuation.  Another study showed that sound localization was not improved, but the effect of the head shadow was reduced. 
This study is a retrospective study based on PTA lacks in details on otological findings, history of duration of symptoms, associated features (tinnitus, vertigo, etc.), associated medical conditions, etiology, etc., Hence, a prospective study has been started in the department on USNHL to address these issues.
| Conclusion|| |
Our study concluded that SNHL type is the most common type of hearing impairment among patients complaining of HL. The limited work has been published on incidence, characteristics, and causes of pure USNHL. The functional and psychological impacts of USNHL are underestimated. Limited options are available to help and treat such patients. The usage adaptability and cost constraints of CROS hearing aid are a challenge to manage patients of USNHL. Further studies and researches are required in the field of USNHL to know the incidence, functional and psychological impact, and treatment options.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]
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