Acute Hearing Loss and Tinnitus

Carolyn Chooljian

CLINICAL PRESENTATION

Acute hearing loss (AHL) is defined as hearing loss occurring over 3 days or less and involves the loss of 30 decibels (dB) of hearing over three or more contiguous audiologic frequencies. AHL may present in isolation or with tinnitus and/or vertigo. The presence or absence of associated symptoms is useful in its evaluation. The etiology of AHL may be obvious or obscure. When it is due to trauma of the temporal bone or associated with the effusion of acute otitis media the etiology is readily apparent. However, AHL may also occur spontaneously without an obvious etiology. The patient may complain of hearing loss in one ear or both.

Auditory Pathway

Knowledge of the auditory pathway (1) is helpful in understanding the presentation, type, and cause of AHL. The auditory system can be divided into peripheral and central parts. The peripheral auditory system consists of the external ear, middle ear, and the inner ear located within the temporal bone. The external ear includes the auricle, external auditory canal, and tympanic membrane (TM). The middle ear is an air-filled space that contains the auditory ossicles—the malleus, incus, and stapes. Sound waves reach the TM and are transmitted via the ossicles of the middle ear to the fluid-filled cochlea of the inner ear. The cochlea contains the specialized hearing organ of Corti where sound is converted from mechanical pressure to electrical signals through its neuroepithelial hair cells. Projections from the organ of Corti proceed to the bipolar spiral ganglion. The centrally projecting processes of the spiral ganglion constitute the auditory portion of the eighth cranial nerve, the cochlear nerve. These project to the ventral and dorsal cochlear nuclei, which are located in the brainstem at the level of the lower pons.

The central segment of the auditory system extends from the cochlear nuclei up to the auditory cortex of the temporal lobe. The cochlear nuclei send projections to the superior olivary nucleus of the pons. Here most of the auditory input crosses to the contralateral side via the trapezoid body to form the lateral lemniscus. The lateral lemniscus is the auditory tract that traverses the pons to the inferior colliculus of the midbrain. At this level the inferior colliculi intermingle information from both ears. Inferior colliculi axons project on to the medial geniculate bodies of the thalamus. From there the auditory radiations project to the primary auditory cortex of the temporal lobe. Each auditory cortex receives input from both ears. As a result, lesions of the central auditory pathway cause bilateral hearing loss, though the loss is greater on the contralateral side. Peripheral lesions cause unilateral ipsilateral loss. Cortical deafness only occurs when both temporal lobes are injured. Unilateral temporal insults do not clinically affect hearing.

Types of Hearing Loss

Hearing loss is divided into two broad categories—conductive hearing loss (CHL) and sensorineural hearing loss (SNHL). Mixed hearing loss is a combination of the two.

CHL involves problems of the external and middle ear. SNHL involves the cochlea, cochlear division of the eighth cranial nerve, and the central nervous system portion of the auditory pathway.

Tinnitus

Tinnitus is the perception of sound without an auditory stimulus. Ninety-four percentage of healthy young people report perceiving tinnitus at times (2). Ringing, buzzing, whistling, and humming are some descriptors of tinnitus. It may be a symptom of disease though not necessarily. Fifty percentage of persons with sudden hearing loss will describe associated tinnitus. Tinnitus may be associated with CHL or SNHL.

DIFFERENTIAL DIAGNOSIS

Acute Conductive Hearing Loss

Acute causes of CHL include cerumen impaction of the external auditory canal, TM perforation secondary to trauma or infection, acute effusion of the middle ear from otitis media, ossicular chain dysfunction, and eustachian tube obstruction. TM perforation leads to 15 to 20 dB of CHL. Acute barotrauma from the inability to equalize pressure between the external and middle ear during scuba diving or altitude changes during air flight or driving can lead to painful, temporary CHL.

Acute Sensorineural Hearing Loss

SNHL has many causes including ototoxic drugs, acute infections, chronic meningitis, loud noise, vascular disease, barotrauma, Ménière’s disease, multiple sclerosis, migraine (3), and autoimmune inner ear disease (AIED). Acute SNHL may also be idiopathic. Drugs known to cause ototoxicity include aminoglycosides, intravenous erythromycin, loop diuretics, salicylates, antineoplastic agents such as cisplatin and vincristine, and has been newly reported in patients using the phosphodiesterase five inhibitors sildenafil, tadalafil, and vardenafil for erectile dysfunction (4). Aminoglycoside ototoxicity is related to the total serum concentration of the drug, though it is heightened by increasing age and appears to have a genetic component. Tinnitus is a common early symptom. Loop diuretic–associated ototoxicity is usually temporary, but can be permanent. Salicylate concentrations of 20 to 50 mg/dL can cause up to 30 dB of hearing loss. Tinnitus increases as the plasma levels exceed 40 mg/dL. Bacterial meningitis causes hearing loss in up to 35% of infections by injuring the inner hair cells of the cochlea. Viruses that have caused hearing loss include measles, mumps, rubella, CMV, herpes zoster, herpes simplex, and HIV. Spirochete infections of early and late syphilis and Lyme disease may cause unilateral or bilateral SNHL. Syphilitic hearing loss may be fluctuating and associated with vertigo resembling Ménière’s disease. Chronic meningitis involving the auditory nerve—both infectious and noninfectious—may cause or present with acute SNHL. Sarcoid, mycotic, lymphomatous, carcinomatous, and tuberculous infiltrations have been described. Other cranial nerves may or may not be involved. Extreme noise levels may lead to cochlear spiral ganglion degeneration and SNHL by damaging sensory hair cells. This is often temporary, though prolonged exposure to sounds above 85 dB may cause permanent hearing loss. Hearing loss has also been described with automobile airbag detonation (5). Cerebrovascular accidents and transient ischemic attacks involving the vertebrobasilar circulation may lead to acute SNHL. The anterior-inferior cerebellar artery serves the lateral pons, middle cerebellar peduncle, and the inner ear. Strokes in this distribution cause vertigo, severe SNHL loss, and ataxia (6). Infarction in the distribution of the superior cerebellar artery leads to contralateral partial hearing loss by involving the lateral lemniscus. Cochlear anoxia due to poor microcirculation or vasculitis may cause acute SNHL. Hyperviscosity states in Waldenstrom macroglobulinemia and polycythemia can impair cochlear circulation. Spontaneous hemorrhage of the inner ear has occurred with leukemia, sickle cell disease, thalassemia, subarachnoid hemorrhage, trauma, and hypercoagulable states. Sudden SNHL and vertigo occurring within hours or days may be due to a perilymphatic fistula (PLF). PLF from rupture of the round or oval window between the air-filled middle ear and fluid-filled inner ear may be caused by barometric pressure changes from scuba diving, airplane flight, mountain travel, and even vigorous sneezing. Ménière’s disease is a syndrome that causes recurrent fluctuating hearing loss, vertigo, and tinnitus. The hearing loss usually resolves within 24 hours, though it eventually becomes permanent. Multiple sclerosis may present with acute SNHL or vertigo. Migraine headache can be associated with acute SNHL, likely due to vasospasm, and may cause migrainous infarction (3). AIED is an immune-mediated cause of SNHL which may present with rapidly progressive hearing loss. It has been associated with relapsing polychondritis, Wegener granulomatosis, systemic lupus erythematosus, rheumatoid arthritis, polyarteritis nodosa, Behcet syndrome, giant cell arteritis, sarcoidosis, and Cogan Syndrome—an interstitial keratitis and vestibuloauditory syndrome which presents with abrupt vertigo, tinnitus, hearing loss, and ataxia. AIED with immune-mediated hearing loss but without systemic symptoms can present as rapidly progressive bilateral deafness as well. Sudden idiopathic SNHL may present acutely with immediate onset or progressive hearing loss over 3 days. It may be bilateral but is unilateral in 90%. Four thousand new cases/year occur in the United States. Any age group may be affected, though it occurs more often between ages of 30 and 60 years. Associated symptoms may include vertigo, tinnitus, or both. The natural history of acute idiopathic SNHL is complete recovery without medical intervention in as many as two-thirds, often within first 3 days to 2 weeks. Hearing worsens over time in 15% (7).

Mixed Hearing Loss (CHL Plus SNHL)

Processes that extensively involve the temporal bone such as tuberculosis and trauma can cause mixed hearing loss. Temporal bone fractures can be longitudinal or transverse, though 70% to 90% are longitudinal. AHL associated with longitudinal fractures involving the external auditory canal, middle ear, and long axis of the petrous pyramid is predominantly CHL, though SNHL occurs in 35% and facial nerve paralysis in 15%. Transverse fractures involving the cochlea and/or auditory nerve can cause total sudden SNHL and may be associated with facial nerve paralysis as well. Penetrating trauma can cause both CHL and SNHL depending on the trajectory and force of the missile.

Blast injuries can cause TM disruption, ossicular discontinuity, cochlear injury, and temporal bone fracture, leading to CHL and SNHL. If a PLF develops, there may be progressive hearing loss and disequilibrium. Lightning and electrocution may produce TM perforation and CHL as well as temporal bone fracture–related SNHL. Bilateral oval window PLF from lightning strike can cause SNHL. Cerebellopontine angle tumors may present with AHL in as many as 20%. Unilateral tinnitus is often present. Meningiomas and cholesteatomas also have presented with AHL. Primary or metastatic tumors to the temporal bone may cause CHL or SNHL. Breast, prostate, and renal cell carcinoma are the most common metastatic tumor types.

ACUTE HEARING LOSS AND ASSOCIATED SYMPTOMS

AHL and Tinnitus

Acute CHL due to otitis media as well as cerumen impaction may have associated tinnitus. Acute SNHL is associated with tinnitus in Ménière’s disease and other causes of sudden SNHL such as ototoxic drugs including salicylates and loop diuretics. Sixty-five percentage of patients with vestibular schwannomas will have constant tinnitus. Pulsatile tinnitus may be a sign of neoplasm; arterial, venous, and intracranial hypertension; and great vessel bruits. Paragangliomas (glomus jugulare tumors) present initially with pulsatile tinnitus and CHL.

AHL and Vertigo

Vertigo can be associated with both CHL and SNHL. Labyrinthine disorders, PLF, Ménière’s disease, multiple sclerosis, and cerebellopontine angle tumors can cause both. Brainstem, cerebellar, and higher causes of vertigo do not usually affect hearing (8).

ED EVALUATION

The ED evaluation of AHL should include a directed history and physical examination regarding the hearing loss complaint; an assessment of hearing, differentiating between CHL and SNHL; recognition of the presence of tinnitus, vertigo, and other focal neurologic findings as well as underlying diseases such as cancer and autoimmune disease; and assessment of the medication list for ototoxic medications.

The ED physician’s tools to differentiate CHL from SNHL include the tuning fork tests. Using a 256- or 512-Hz tuning fork, the Weber test is performed by placing the tuning fork on the patient’s forehead or front teeth. Normally sound is heard the same in both ears. With CHL sound is louder in the poorer-hearing ear (lateralizes to the bad ear). In SNHL sound is louder in the better-hearing ear (lateralizes to the good ear). The Rinne test is performed by first placing the tuning fork on the mastoid bone. When the patient no longer hears sound, the fork is then placed at the auditory meatus. Normally sound should still be heard because air conduction is greater than bone conduction. Inability to hear in front of the ear indicates CHL. In SNHL hearing at both positions will be decreased.

CT scan of the temporal bone is indicated in the setting of head trauma and AHL. CT is best at evaluating fractures and the integrity of the middle ear ossicular chain. MRI is best for fluid, blood, and soft tissue masses. Nontraumatic acute idiopathic SNHL is best evaluated by MRI with gadolinium contrast. Routine laboratory tests and CT scan of the head are not recommended in the evaluation of acute idiopathic SNHL (9). Tinnitus with concerning characteristics—persistent unilateral, pulsating, or fluctuating, and associated with vertigo warrants investigation.