Sudden Hearing Loss

Enrique Perez

Laura J Bontempo

THE CLINICAL CHALLENGE

The rapid onset of unilateral or bilateral hearing loss can be a devastating event. Beyond the immediate sensory disorientation, which can lead to difficulty with sound localization and the ability to understand speech, particularly in noisy environments, persistence of hearing loss can significantly impact quality of life. This impact is even more pronounced in patients who experience hearing loss along with other common coexisting symptoms such as vertigo and tinnitus.¹

Sudden hearing loss is a subjective complaint of rapid-onset unilateral or bilateral hearing impairment. It is characterized as sensorineural, conductive, or mixed types, depending on the underlying mechanism. Acute-onset sensorineural hearing loss (SNHL) can be further classified as sudden sensorineural hearing loss if the onset is rapid and the magnitude is severe. Sudden SNHL is defined as hearing loss of 30 decibels or greater across at least three consecutive frequencies within 72 hours.²

Approximately 15 000 to 60 000 annual visits for sudden hearing loss present to the emergency department (ED), urgent care, or primary care facilities annually.² Alexander et al. found the annual incidence of sudden SNHL in the United States to be 5 to 27 per 100 000 people, increasing with advancing age.³ This figure may underrepresent the incidence of sudden hearing loss because patients may not seek care if they experience spontaneous hearing recovery.

PATHOPHYSIOLOGY

Whether sudden or not, SNHL is generally considered a byproduct of cochlear and/or auditory neural pathway dysfunction and hence is termed “nerve-type hearing loss.” Damage to cochlear hair cells or ischemic injury to the auditory nerve are two common pathophysiologic processes shared by various conditions leading to SNHL. Whereas sudden SNHL may be idiopathic, non-idiopathic forms of sudden SNHL include Meniere disease, noise-induced hearing loss, labyrinthine fistulas, congenital hearing loss, cerebrovascular accidents, and vestibular schwannomas.³ Furthermore, although most cases of sudden SNHL occur unilaterally, various conditions may be associated with bilateral sudden SNHL. Bilateral loss is very rarely idiopathic, so its presence should prompt further investigation into possible underlying etiologies. Table 6.1 lists a multitude of diseases associated with bilateral sudden SNHL and their various associated features.²

When possible, SNHL must be differentiated from conductive hearing loss (CHL). Natural conduction of sound through the ear canal occurs via pressure changes in a column of air that leads to displacement of the tympanic membrane (TM) and subsequent movement of the coupled middle ear ossicular chain. Through a highly synchronized mechanism, this movement leads to a mechanical fluid wave in the intracochlear fluid compartments via the piston-like function of the stapes,
the most medial ossicle in the ossicular chain. Disruption in any of these coupled mechanisms for sound conduction will diminish the sound energy delivered to the cochlea and lead to a CHL. Common example of conditions leading to sudden CHL include cerumen impactions, ear canal foreign bodies, ossicular chain disruption secondary to trauma, eardrum perforations, and acute otitis media (AOM). Chronic otitis media with or without cholesteatoma and otosclerosis are other fairly common otologic conditions leading to CHL, but their onset is generally gradual. Sudden hearing loss may also present as a combination of SNHL and CHL. This is termed mixed hearing loss, as may be the case with some AOM infections. Ultimately, a hearing test or audiogram must be carried out to confirm a specific diagnosis.

TABLE 6.1 Selected Conditions That May Be Associated With Bilateral Sudden Sensorineural Hearing Loss

Cause	Other Features
Infection (viral, including herpes simplex virus, varicella zoster virus, human immunodeficiency virus, and others; bacterial; mycoplasma; Lyme; tuberculosis; syphilis; fungal)	Headache, fever, other cranial nerve palsies, abnormal cerebrospinal fluid commonly seen in meningitis; pinna or ear canal vesicles and facial weakness are often seen in varicella zoster virus (Ramsay Hunt syndrome/herpes zoster oticus)
Autoimmune inner ear disease	Hearing fluctuation, vertigo
Ototoxic medication	Vestibular loss, oscillopsia
Trauma	Temporal bone fracture with possible Battle sign; cochlear concussion without visible fracture; barotrauma
Lead poisoning	Learning disabilities, other stigmata of lead poisoning
Genetic disorders	May be syndromic or nonsyndromic and may present later in life
Mitochondrial disorders, including MELAS (metabolic encephalopathy, lactic acidosis, and stroke-like episodes) and others	Confusion, stroke-like spells, elevated lactate, MRI white matter changes; others with variable phenotypes
Stroke	Vertigo, dysarthria, facial weakness, ataxia, nystagmus, unilateral numbness, abnormal CT or MRI or MR angiogram of the vertebrobasilar vasculature
Cogan syndrome	Non-syphilitic interstitial keratitis of the cornea, hearing loss, vertigo
Neoplastic (neurofibromatosis II, bilateral vestibular schwannomas, carcinomatous meningitis, intravascular lymphomatosis, others)	Abnormal brain MRI, cerebrovascular imaging study, or cerebrospinal fluid
Sarcoidosis	Pulmonary symptoms, bilateral vestibular loss, elevated angiotensin-converting enzyme level, abnormal Gallium scan
Hyperviscosity syndrome	Mucous membrane bleeding, neurologic and pulmonary symptoms, associated retinopathy
CT, computed tomography; MR, magnetic resonance; MRI, magnetic resonance imaging. From Chandrasekhar SS, Tsai Do BS, Schwartz SR, et al. Clinical practice guideline: sudden hearing loss (update). Otolaryngol Head Neck Surg. 2019;161(1_suppl):S1-S45. Table 7.

While a patient with complaints of sudden hearing loss may have any one of the three forms of hearing loss, it is most important to recognize sudden SNHL in a timely fashion. Unlike most forms of sudden CHL, sudden SNHL is considered an “otolaryngologic emergency” because it may become an irreversible condition unless urgently intervened upon.⁴

Noise-induced hearing loss is perhaps one of the most common causes of non-idiopathic sudden SNHL. Although often unilateral, it can also be bilateral depending on the circumstances of the noise exposure. Luckily, most forms of noise-induced sudden hearing loss reverse spontaneously within 24 to 48 hours. Nonetheless, recurring exposure to hazardous noise can often lead to progressive SNHL over time.

APPROACH/THE FOCUSED EXAM

History

Historical features that will help a clinician narrow the differential diagnosis of a patient with sudden hearing loss include unilaterality or bilaterality, symptom recurrence, associated trauma, and the presence or absence of associated symptoms.

Clinicians can make a fairly accurate determination on whether a patient is likely experiencing SNHL or CHL based on history alone. Whether sudden or not, CHL is more often associated with a history of penetrating or nonpenetrating trauma, or infectious symptoms such as ear drainage and otalgia. The patient may also report a history of recurring infections or prior otologic procedures. On the contrary, SNHL is more often associated with other inner ear-like symptoms such as vertigo, tinnitus, or aural fullness.

Vertigo complaints are present in 30% to 60% of cases of sudden SNHL.⁵^,⁶^,⁷ This may also indicate a poor hearing prognosis and is often associated with worse degrees of hearing loss.⁶ New-onset tinnitus is present in almost every case of sudden SNHL, and while having little bearing on the prognosis, it can lead to functional and psychological distress.⁸ Importantly, when evaluating patients with acute hearing loss, it is critical to remember that erroneously labeling a case of sudden SNHL as sudden CHL can lead to delays in treatment and potentially worse hearing outcomes.

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