Adult Sensorineural Hearing Loss
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11 Adult Sensorineural Hearing Loss
Join us for a discussion about sensorineural hearing loss (SNHL) in adults, a topic that will be relevant to a variety of fields in medicine!
Show Notes
Intro:
Hey everyone and welcome to The Oto Approach, a podcast created by medical students for medical students, to teach you about all things otolaryngology. I'm your host Aileen, and today we're doing part 2 of Adult Hearing Loss. Tag along for a discussion about this common presentation within otolaryngology and primary care settings.
We’ll start with a summary of the anatomy of the ear. This was already covered in the part 1 of adult hearing loss episode, so feel free to skip ahead if you feel you already have a good handle on this! The anatomy of the ear is uniquely constructed to allow for hearing. The ear is divided into three segments: the outer, middle and inner ear. The outer, comprised of the auricle or pinna and external auditory canal, is the part with the most contact with the external world.5 The outer ear or auricle features including the helix, antihelix, tragus and antitragus effectively “catch” sound waves and funnel them down to the external auditory canal.6 The middle ear is an air-filled space, which is divided into the epitympanic recess and tympanic chamber, and contains the ossicles.5 The tympanic membrane separates the outer ear and the middle ear. Sound waves vibrate the tympanic membrane. The ossicles, including the malleus, the incus and the stapes, are bony structures suspended by ligaments which allow them to move and transmit vibrations to the inner ear.5 The inner ear contains the vestibular system, responsible for balance and equilibrium, and the cochlea, which is essential for hearing.7 The piston-like motion of the stapes is effective in transmitting energy to the cochlea through the oval window, resulting in movement of the fluid of the inner ear.6 The cochlea is composed of 3 main fluid compartments, the scala tympani and scala vestibuli containing perilymphatic fluid, and the scala media, containing endolymphatic fluid.7 The Organ of Corti contains inner and outer hair cells, which allow for the transduction of electrical auditory signals.8 The stiffness and size of the hair cells vary throughout the cochlea, which allows the cells to respond to a range of frequencies.8 These are distributed throughout the cochlea such that cells that respond to low frequencies are located near the apex of the cochlea, whereas the cells that respond to high frequencies are at the base of the cochlea. The vibration of the sound waves through the fluid bends the stereocilia on these hair cells. This mechanical energy is then converted to electrical energy which is transmitted to the central nervous system via the cochlear or auditory nerve, a branch of the cranial nerve VIII (8), or the vestibulocochlear nerve.8 The other branch, the vestibular nerve innervates the organs of balance in the inner ear, the semicircular canals and otolith organs and conveys sensory impulses regarding the head and body motion to the brain.9
Hearing loss may be classified into three types; Sensorineural, Conductive and Mixed. Sensorineural hearing loss involves the inner ear, the cochlea, or the auditory nerve. Conductive hearing loss involves any cause that limits the amount of external sound from gaining access to the inner ear, typically outer or middle ear pathologies. Mixed hearing loss is a combination of sensorineural and conductive loss.6
In our last episode we reviewed problems associated with the outer ear and middle ear which resulted in conductive hearing loss. Now we are going to focus on the pathologies in the inner ear, which cause sensorineural hearing loss.
(prez buh cue sis) Presbycusis or age-related hearing loss is a common cause of sensorineural hearing loss, affecting approximately one in three in the United states between 65 and 74 years of age, and nearly half of those older than 75.20 It is characterized by gradual bilateral loss of high-frequency hearing associated with advancing age. Common presentation includes an individual struggling to hear or understand speech in environments with noisy backgrounds, difficulty understanding consonants, and inability to hear high-pitched noises.6 Hearing aids are the mainstay for improving hearing and quality of life with those with presbycusis.
Infection can also cause sensorineural hearing loss. The most common infection of the inner ear in adults is viral cochleitis.6 Viral cochleitis typically presents as sudden sensorineural hearing loss, while other symptoms of vertigo, facial paralysis or pain are less frequent.6 Such infections can damage the inner ear hair cells and therefore, impair hearing. Cochlear implants may be used in this context, and postlingual adults with profound sensorineural hearing loss bilaterally often receive the most benefit from this approach.6
Meniere’s disease is a disorder of the inner ear mainly affecting adults between 30 and 60 years old, and causes symptoms including sensation of fullness in the ear, hearing loss, tinnitus and recurrent bouts of vertigo.21 It is a progressive disease with fluctuating episodes of symptoms. The vertigo resolves eventually, but hearing loss can become permanent and progress to involve all frequencies. Treatment can involve betahistine plus thiazide diuretic, caffeine restriction, intratympanic corticosteroids, intratympanic gentamicin, psychological support, salt restriction and vestibular rehabilitation.21
Other inner ear causes of hearing loss include tumors, the most common being an acoustic neuroma or vestibular schwannoma, a benign tumor originating from the vestibular portion of the eighth cranial nerve. The presentation would include the primary symptom of unilateral sensorineural hearing loss and may also include unilateral tinnitus, disequilibrium, dizziness, headaches, or facial muscular twitching.6 The mainstays of treatment include observation, surgical excision, and radiation.22
Trauma can also affect the inner ear causing sensorineural hearing loss, including penetrating trauma and blunt force trauma.6 Metabolic abnormalities, such as diabetes, have been associated with this type of hearing loss as well. Additionally autoimmune inner ear disease has been defined as a cause of bilateral sensorineural hearing loss. Treatment includes steroid and immunosuppressive therapy.23 There are also iatrogenic causes, in that surgical procedures or medications can damage the inner ear and subsequent hearing ability. The most commonly used drugs that are ototoxic are antibiotics and chemotherapy agents and sensorineural loss associated with such drugs is permanent.6 Other drugs are known to cause reversible hearing loss, including high-dose aspirin or other salicylates, loop diuretics, and antimalarial medications such as quinine.6
Sudden sensorineural hearing loss
Sudden sensorineural hearing loss (SSNHL) in adults is an emergency and an important presentation to be aware of. It is defined as “sensorineural hearing loss of 30dB or greater over at least three contiguous audiometric frequencies occurring within a 72-hr period.”24 The majority of cases are idiopathic, however the most frequent causes identified include infectious, otologic, traumatic, vascular, and neoplastic.24 Idiopathic sudden sensorineural hearing loss is most common in 43 to 53 year olds.25 The typical presentation of patients is immediate or rapid hearing loss or loss of hearing upon awakening. The hearing loss is typically unilateral but up to 3% may experience bilateral loss.26 More than 90% of those with unilateral hearing loss have ipsilateral tinnitus and 20-60% experience vertigo.26
A history and physical examination are necessary as well as audiometry to establish the diagnosis, which should be conducted as soon as possible but should not delay treatment. MRI is also the preferred imaging technique in this clinical scenario and should be completed within 3 months of onset.26 Laboratory studies can also be completed to rule out other causes including hypothyroidism, hyperviscosity syndrome or vasculitis. If there is a cause identified, treating the underlying etiology is a critical component of the treatment.
For all patients the initial treatment suggested includes glucocorticoids, which can be administered systemically, intratympanically or in combination, ideally started within the first 5 days of symptom onset.26 Hyperbaric oxygen therapy may also be utilized as an adjuvant to the initial steroids, however there is further research required to support this approach. Although high-quality evidence is lacking in the support of adding antiviral therapy to the approach, if a patient is identified within the first 48 hours of their symptom onset, an antiviral may be offered due to the potential benefits and limited risk.26 The overall prognosis for idiopathic Sudden sensorineural hearing loss is favorable, with about two-thirds of patients recovering some degree of their hearing, typically within 3 months. However if improvement is not noted within this time period it is unlikely to follow after.26 This is a presentation to be familiar within primary care and otolaryngology, as early recognition and treatment is critical.
History
Now we are going to review some of the important aspects of a history in the context of adult hearing loss. Any patient presenting with hearing loss should have a full auditory history and examination. It is critical to ask about onset and progression and if they are experiencing unilateral or bilateral loss. Through the history you can also gain an understanding of how the hearing loss affects the patient, asking about how well they can understand spoken words, if the problem is mainly with noise backgrounds or if it is equally present in quiet settings as well. Additionally, you can ask about associated tinnitus, vertigo or disequilibrium, or if they have experienced headache or visual disturbances around the time of the episodes of hearing loss. It is also important to ask about pain or drainage from the ear. It is essential to inquire about some of the causes that we reviewed such as trauma, major infection, previous ear surgery and other medical conditions, such as diabetes, coronary artery disease and autoimmune diseases. Social history is also important in this clinical context and asking about their job and the nature of noise level at the workplace. Excessive noise exposure can affect the degree of (prez buh cue sis) presbycusis, or age related hearing loss, that develops, and exposure to loud noises can cause high-frequency sensorineural hearing loss, but again, we will get more into sensorineural hearing loss in a future episode- so stay tuned for that!6 Family history of hearing loss is also important information to gather. Finally, inquiring about medications, both prescribed and over the counter.
Physical and Investigations:
There are some aspects of the physical examination and testing that can occur in a primary care office setting, however many patients also require formal audiological testing or other specialized tests. There are also a variety of free smartphone apps that can perform screening audiograms, including “uHear” which has been validated in a number of peer reviewed studies against the gold standard pure tone audiometry.16 This technology is particularly helpful in situations where formal audiograms are not accessible.
In the office setting, methods to evaluate hearing include whispered voice test, tone-emitting otoscope, questionnaires and tuning forks. The whispered voice test is often introduced to medical students in clinical skills and involves standing at arm’s length behind the patient, as they cover one ear, and whispering a sequence of words such as “ninety-nine,” then asking them to repeat what they heard.24 This is repeated for the opposite ear. Screening for hearing loss with a tone-emitting otoscope has been shown to be the most effective screening method, compared to questionnaires.
Tuning forks can be utilized to perform Weber and Rinne tests, which can help distinguish the location and type of hearing loss the patient is experiencing. The Weber test is conducted by placing the vibrating tuning fork on the midline of the forehead, or bridge of the nose, then asking the patient where the loudest sound is experienced, on the right, left or middle. The vibrations will be conducted through the bone to the cochlea, and in normal hearing or symmetrical hearing loss the sound is heard in the middle, equal on both sides.25 The Weber test suggests sensorineural hearing loss if the sound is louder on the patient’s reported “good” side, and conductive hearing loss is considered if the sound is louder on the bad side.24 Rinne test differentiates sound transmitted through air conduction from bone conduction via the mastoid bone.26 The tuning fork handle is placed on the mastoid bone behind the ear and the patient is asked to report when the sound is no longer audible, then the fork is brought away from the bone near the ear canal and asked if they can hear the sound now. Another way to complete this test is asking the patient if the tuning fork is louder on the bone or by the ear. A normal test result would be hearing the sound again once the fork is brought in close proximity to the ear or hearing it louder when by the ear, demonstrating air conduction is better than bone conduction.24 The Weber and Rinne test work together to help differentiate conductive and sensorineural hearing loss. An abnormal Rinne test suggests conductive loss, particularly if the Weber test also lateralizes to that side. In the case that the Rinne test is normal in an ear where the Weber test showed lateralization to that same ear, the Rinne test must be conducted on the opposite ear. If this test is normal in this ear, it is suggestive of sensorineural hearing loss.24
The auricle and external auditory canal should also be examined. An otoscope can be utilized to visualize the tympanic membrane and recognize any middle ear abnormalities, such as perforations in the tympanic membrane. Pneumatic otoscopy can be used to assess the mobility of the tympanic membrane. When air is forced into the auditory canal, the tympanic membrane should move down and when the pressure is released the tympanic membrane should be pulled outward.17 Formal audiologic assessment should be performed for patients who do not have a known cause for the hearing loss.
When an etiology for hearing loss is not clear, referral to an otolaryngologist is recommended.
Sudden sensorineural hearing loss
Sudden sensorineural hearing loss (SSNHL) in adults is an emergency and an important presentation to be aware of. It is defined as “sensorineural hearing loss of 30dB or greater over at least three contiguous audiometric frequencies occurring within a 72-hr period.”24 The majority of cases are idiopathic, however the most frequent causes identified include infectious, otologic, traumatic, vascular, and neoplastic.24 Idiopathic sudden sensorineural hearing loss is most common in 43 to 53 year olds.25 The typical presentation of patients is immediate or rapid hearing loss or loss of hearing upon awakening. The hearing loss is typically unilateral but up to 3% may experience bilateral loss.26 More than 90% of those with unilateral hearing loss have ipsilateral tinnitus and 20-60% experience vertigo.26
A history and physical examination are necessary as well as audiometry to establish the diagnosis, which should be conducted as soon as possible but should not delay treatment. MRI is also the preferred imaging technique in this clinical scenario and should be completed within 3 months of onset.26 Laboratory studies can also be completed to rule out other causes including hypothyroidism, hyperviscosity syndrome or vasculitis. If there is a cause identified, treating the underlying etiology is a critical component of the treatment.
For all patients the initial treatment suggested includes glucocorticoids, which can be administered systemically, intratympanically or in combination, ideally started within the first 5 days of symptom onset.26 Hyperbaric oxygen therapy may also be utilized as an adjuvant to the initial steroids, however there is further research required to support this approach. Although high-quality evidence is lacking in the support of adding antiviral therapy to the approach, if a patient is identified within the first 48 hours of their symptom onset, an antiviral may be offered due to the potential benefits and limited risk.26 The overall prognosis for idiopathic Sudden sensorineural hearing loss is favorable, with about two-thirds of patients recovering some degree of their hearing, typically within 3 months. However if improvement is not noted within this time period it is unlikely to follow after.26 This is a presentation to be familiar within primary care and otolaryngology, as early recognition and treatment is critical.
Clinical Pearls
Here are some clinical pearls from our resident team, including good FYIs and frequently quizzed topics on ENT rotations:
Interpreting audiograms is a key skill for otolaryngologists and can be especially beneficial for clerks when reviewing hearing tests. Here are some pearls related to audiogram interpretation for conductive hearing loss:
A notched decrease in hearing decibels at ~2000 Hz is called Carhart’s notch and can be a classic sign of otosclerosis.
A notched decrease in hearing decibels at ~4000 Hz is often associated with noise-induced hearing loss.
Adults with age-related hearing loss otherwise known as presbycusis will have decreasing hearing decibels in the higher frequencies.
Patients with conductive hearing loss will classically have a “air-bone gap” where hearing tested through the air is reduced compared to hearing through the bone. As bone related hearing relies solely on sensorineural hearing loss and air related hearing relies on sensorineural as well as conductive hearing loss.
We would like to extend our sincerest thanks to the Saint John Regional Hospital Department of Surgery within the Horizon Health Network for their generous support.
Thank you so much for listening to our podcast! We hope you’ll tune in to our next episode! Please head to our website at www.theotoapproach.com for our show notes, and to sign up for our newsletter to stay up to date with our latest episodes.
References:
21. Wright T. Menière’s disease. BMJ Clin Evid. 2015;2015:0505.