Sudden hearing loss (SHL) is described as the rapid onset of deafness that may occur abruptly or in a progressive manner. Most cases are idiopathic. Typically, there is unilateral involvement.
Sudden hearing loss (SHL) is considered an otologic emergency. Hence, the earlier the assessment and treatment, the better the prognosis. The cause should be identified promptly. Furthermore, according to the American Academy of Otolaryngology-Head and Neck Surgery Foundation (AAO-HNSF), the medical team should differentiate SHL from conductive hearing loss (CHL).
The affected individuals typically report difficulty with understanding group conversations and with listening in the setting of background noise. Also, sounds appear too muffled and may even be loud in these patients as they experience trouble high pitched sounds. Other manifestations include dizziness, imbalance, and tinnitus. Some individuals will realize the hearing loss when they first wake up while others notice it when they use the phone with the affected ear. Additionally, patients may describe hearing a popping sound prior to the onset of deafness.
In drug-induced hearing loss, the features may include unilateral or bilateral tinnitus, the worsening of tinnitus, fullness or pressure in the ears, hearing loss in the contralateral ear, and/or vertigo with motion.
This consists of a thorough head and neck assessment including otologic and neurologic evaluation. In patients with a particular disorder, other manifestations may present.
During the evaluation, the clinician should ascertain the onset, course, and whether there were any recent events. Additionally, the clinician should identify all prescription and over-the-counter medications and risk factors. Other notable details include whether the involvement is bilateral and if the hearing loss is an initial or a recurring episode. The workup further includes a physical exam with a focus on neurologic testing.
This hearing test differentiates between the primary causes of hearing loss which may originate from a conductive or sensorineural abnormality. Also, the range or severity can be assessed with this test.
Blood tests and imaging such as magnetic resonance imaging (MRI) may be useful. The clinician will obtain studies based on the overall clinical picture.
The therapeutic approach depends on the cause of the hearing loss.
SHL can be treated with glucocorticoids, which can be administered through a transtympanic injection to avoid systemic adverse effects. It may also be given orally as both routes are effective. Additionally, antiviral drugs such as valacyclovir or famciclovir may also be given. Note that in the case of ototoxicity, the offending drug should be discontinued.
Hearing aids and cochlear implants are potential options to improve or recover partial hearing.
The prognosis of SHL is usually good as depicted by the 47% to 63% of cases that result in spontaneous resolution. These individuals improve within two weeks. The factors predictive of a poor outcome are 1) age less than 15 years or greater than 65, 2) erythrocyte sedimentation rate (ESR) level above 25, 3) vestibular changes on electronystagmography (ENG), 4) bilateral hearing loss, 5) profound hearing loss, and 6) occurrence of vertigo. The latter is associated with smaller recovery rates and more severe hearing loss, which are likely attributed to the close proximity of the cochlea and vestibule. In cases with ototoxicity, the prognosis depends on the drug and its dose. The recovery from hearing loss due to aspirin and diuretics occurs within 24 hours whereas overdosing with antibiotics and chemotherapy agents may cause permanent loss.
While the majority of sudden deafness cases are idiopathic, the others occur following a previous event or another unidentified etiology. Also, certain patients will manifest with deafness as a feature of a particular disorder.
Some patients with immediate hearing loss will have preceding events such as loud sounds, blunt trauma to the temporal bone, or a severe concussion. Also, pressure changes due to events such as diving or other vigorous physical activities may lead to the development of a perilymphatic fistula in the ear, which causes abrupt hearing loss. In individuals with congenital fistulas, trauma or pressure alterations can produce deafness.
Ototoxic medications such as aspirin, certain antibiotics, loop diuretics, chemotherapy agents and anti-inflammatory drugs can cause rapid onset of hearing loss. Additionally, there is a rare mitochondrial disorder associated with aminoglycoside ototoxicity.
Bacterial meningitis, Lyme disease, mumps, herpes, measles, and other viral illnesses may affect the cochlea and vestibular apparatus, resulting in a rapid onset of hearing loss. Furthermore, mumps and herpes are the most predominant viral etiologies in developed countries.
Waldenström macroglobulinemia, sickle cell disease, and certain types of leukemia may lead to deafness albeit they are rare causes. Acoustic neuroma, multiple sclerosis, Ménière's disease, and cerebellar stroke can feature hearing loss as the initial presenting symptom or in conjunction with other manifestations. Cogan syndrome is a rare autoimmune process targeting an antigen in the ear or cornea causing vestibulo-auditory symptoms in more than half of patients.
In the United States, the yearly incidence of SSHL ranges from 5 to 20 cases per 100,000 population. However, the actual number is likely greater since this condition is frequently underreported. The reason for this is because symptoms may spontaneously resolve before the patient seeks medical care.
The patient demographics overall show no gender preference. Furthermore, several studies report a mild predominance in males while another large investigation tilted the distribution to females .
With regards to age, sudden hearing loss affects all ages suggesting a multifactorial cause. The peak age group is the sixth decade of life while the median age runs from 40 to 54 years old. Additionally, children and the elderly have a smaller incidence.
Finally, bilateral SSHL is more likely to manifest at younger ages than unilateral involvement .
Idiopathic causes of SHL include 1) viral infections of the labyrinthine, 2) vascular insufficiency of the labyrinthine, 3) rupture of the intracochlear membrane, and 4) autoimmune reactions in the inner ear.
Several uncontrolled studies observe that 17% to 33% of patients with idiopathic SHL report a recent viral illness. In other studies, patients with idiopathic SHL have shown a greater frequency of herpesvirus seroconversion versus the control subjects.
Additionally, histopathologic evaluation of the temporal bone in patients with idiopathic SHL revealed abnormalities that can be associated with viral infections. Findings include the depletion of neurons, hair, and other cells as well as atrophy of the tectorial membrane and stria vascularis. These observations were also demonstrated in hearing loss patients affected with mumps, measles, and maternal rubella. Furthermore, one study reported that 9 of 130 cases of idiopathic SHL were positive for immunoglobulin M (IgM) antibodies to mumps .
Thrombosis, embolus, or hypoperfusion of the cochlea could be detrimental to its function as this structure lacks supply from collateral vessels. Therefore, any vascular compromise affects the cochlea. The histological findings in the temporal bone of individuals with cochlear damage secondary to vessel occlusion include the presence of intracochlear bleeding, fibrosis, and ossification.
Risk factors for idiopathic SHL were evaluated in one study that was designed to identify a correlation between this condition and coronary artery disease. Elevated cholesterol and reduced high-density lipids (HDL) levels were not found to be risked factors although increased fibrinogen, smoking, and GPIa C807T polymorphism were.
However, a different investigation with an age-matched control group concluded that idiopathic SHL was observed to be 1.6 times greater in those with hypocholesterolemia . This observation may be significant for the management and prevention of sudden hearing loss .
The inner and outer ear are separated by a membrane. If this membrane ruptures, the perilymph leaks into the middle ear. Additionally, the perilymphatic and endolymphatic spaces in the cochlea are divided by a fragile membrane. If this intracochlear membrane ruptures, the ensuing mixture of the perilymph and endolymph will result in a change in the endocochlear potential. This latter mechanism was corroborated by several studies   . Hence, if one or both membranes are jeopardized, hearing loss is a consequence.
Autoimmune rheumatologic conditions such as Cogan syndrome, systemic lupus erythematosus, and others are associated with hearing loss. Moreover, one prospective study with 51 patients affected with idiopathic SHL demonstrated a link to immune-mediated disorders .
Iron deficiency anemia may be implicated in sudden hearing loss, particularly in individuals 44 years or under .
One strategy to prevent ototoxicity is through better selection of medications if possible, especially in cases when there is an alternative drug with good efficacy. Examples of ototoxic drugs include aspirin (in high doses), loop diuretics, certain antibiotics, chemotherapy agents and anti-inflammatory medications.
Another strategy is avoiding heavy noise exposure since this can damage the hair cells in the ear. In fact, prolonged and repetitive exposure to loud noises may cause SHL.
Sudden hearing loss, also known as sudden sensorineural hearing loss (SSHL), is the rapid onset of deafness that develops abruptly or during a progressive course over several days. Most cases occur due idiopathic causes, in which numerous theories have been postulated to explain the etiologies. In other situations, the deafness may develop secondary to a known event, exposure to loud noise, head trauma, pressure changes, ototoxic medications, bacterial or viral illnesses, vasculitis, or rheumatologic diseases.
The clinical picture typically consists of unilateral involvement, tinnitus, dizziness, and vertigo. Additionally, if SHL is part of a disorder, then features of that condition are also present.
Since this is a medical emergency, the evaluation should be prompt and thorough. The clinician should obtain a full medical history and clarify all preceding events, medications and risk factors associated with hearing loss. Furthermore, the physical exam includes a neurologic focus in addition to tone audiometry. Finally, the management of SHL may indicate the use of glucocorticoids or surgery. If the deafness is a side effect of a particular drug, then the offending agent should be withdrawn. As for long-term effects, some cases will result in spontaneous recovery while others are permanent. Specifically, there are certain factors such as extreme age and vertigo that are overall poor prognostic factors.
Sudden hearing loss is a condition in which a person loses hearing rapidly and abruptly over several days. The sound becomes muffled or decreased. In most cases, only one ear is affected. The causes of this type of deafness are many but are usually unknown in most people. The following are possible causes:
The following are signs of hearing loss:
The clinician will try to identify the cause by evaluating the patient's history, the list of medications, risk factors, and if there are any associated symptoms. Additionally, the clinician will perform a detailed exam including a neurologic one. If any laboratory studies are needed, they will be obtained. The main hearing exam called tone audiometry is the most important test.
Some patients will recover on their own within a few days. Others may require 7 to 14 days. There are patients who will have a permanent hearing loss.