Sudden Hearing Loss
Sudden hearing loss is moderate to severe sensorineural hearing loss that develops suddenly, within a few hours or is noticed on awakening. It affects about 1/5000 to 1/10,000 people each year. Initial hearing loss is typically unilateral (unless drug-induced) and may range in severity from mild to profound. Many also have tinnitus, and some have dizziness, vertigo, or both.
Sudden hearing loss has some causes that differ from chronic hearing loss and must be addressed urgently (1).
The following are common characteristics of sudden hearing loss:
Most cases (see Table: Some Causes of Sudden Hearing Loss) are idiopathic.
Some occur in the course of an obvious explanatory event.
A few represent the initial manifestation of an occult but identifiable disorder.
Idiopathic: There are numerous theories for which some evidence (although conflicting and incomplete) exists. The most promising possibilities include viral infections (particularly involving herpes simplex), autoimmune attacks, and acute microvascular occlusion.
Obvious event: Some causes of sudden hearing loss are readily apparent.
Blunt head trauma with temporal bone fracture or severe concussion involving the cochlea can cause sudden hearing loss.
Large ambient pressure changes (eg, caused by diving) or strenuous activities (eg, weightlifting) can induce a perilymphatic fistula between the middle and inner ear, causing sudden, severe symptoms. Perilymphatic fistula can also be congenital; it can spontaneously cause a sudden loss or loss may occur after trauma or severe pressure changes.
Ototoxic drugs can result in hearing loss occurring sometimes within a day, especially with an overdose (systemically or when applied to a large wound area, such as a burn). There is a rare genetic mitochondrial-transmitted disorder that increases the susceptibility to aminoglycoside ototoxicity.
A number of infections cause sudden hearing loss during or immediately after acute illness. Common causes include bacterial meningitis, Lyme disease, and many viral infections that affect the cochlea (and sometimes the vestibular apparatus). The most common viral causes in the developed world are mumps and herpes. Measles is a very rare cause because most of the population is immunized.
Occult disorders: Sudden hearing loss rarely can be an isolated first manifestation of some disorders that usually have other initial symptoms. For example, sudden hearing loss rarely may be the first manifestation of an acoustic neuroma, multiple sclerosis, Meniere disease, or a small cerebellar stroke. Syphilis reactivation in HIV-infected patients rarely can cause sudden hearing loss.
Cogan syndrome is a rare autoimmune reaction directed against an unknown common autoantigen in the cornea and inner ear; > 50% of patients present with vestibuloauditory symptoms. About 10 to 30% of patients also have a severe systemic vasculitis, which may include life-threatening aortitis.
Some vasculitic disorders can cause hearing loss, some of which is acute. Hematologic disorders, such as Waldenström macroglobulinemia, sickle cell disease, and some forms of leukemia, rarely can cause sudden hearing loss.
Some Causes of Sudden Hearing Loss
Evaluation consists of detecting and quantifying hearing loss and determining etiology (particularly reversible causes).
History of present illness should verify that loss is sudden and not chronic. The history should also note whether loss is unilateral or bilateral and whether there is a current acute event (eg, head injury, barotrauma [particularly a diving injury], infectious illness). Important accompanying symptoms include other otologic symptoms (eg, tinnitus, ear discharge), vestibular symptoms (eg, disorientation in the dark, vertigo), and other neurologic symptoms (eg, headache, weakness or asymmetry of the face, abnormal sense of taste).
Review of systems should seek symptoms of possible causes, including transient, migratory neurologic deficits (multiple sclerosis) and eye irritation and redness (Cogan syndrome).
Past medical history should ask about known HIV or syphilis infection and risk factors for them (eg, multiple sex partners, unprotected intercourse). Family history should note close relatives with hearing loss (suggesting a congenital fistula). Drug history should specifically query current or previous use of ototoxic drugs and whether the patient has known renal insufficiency or renal failure.
The examination focuses on the ears and hearing and on the neurologic examination.
The tympanic membrane is inspected for perforation, drainage, or other lesions. During the neurologic examination, attention should be paid to the cranial nerves (particularly the 5th, 7th, and 8th) and to vestibular and cerebellar function because abnormalities in these areas often occur with tumors of the brain stem and cerebellopontine angle.
Additionally, the eyes are examined for redness and photophobia (possible Cogan syndrome), and the skin is examined for rash (eg, viral infection, syphilis).
Traumatic, ototoxic, and some infectious causes are usually apparent clinically. A patient with perilymphatic fistula may hear an explosive sound in the affected ear when the fistula occurs and may also have sudden vertigo, nystagmus, and tinnitus.
Focal neurologic abnormalities are of particular concern. The 5th cranial nerve, 7th cranial nerve, or both are often affected by tumors that involve the 8th cranial nerve, so loss of facial sensation and weak jaw clench (5th) and hemifacial weakness and taste abnormalities (7th) point to a lesion in that area.
Fluctuating unilateral hearing loss accompanied by aural fullness, tinnitus, and vertigo also suggests Meniere disease. Systemic symptoms suggesting inflammation (eg, fevers, rash, joint pains, mucosal lesions) should raise suspicion of an occult infection or autoimmune disorder.
Patients should have an audiogram, and unless the diagnosis is clearly an acute infection or drug toxicity, most clinicians do gadolinium-enhanced MRI to diagnose inapparent causes, particularly for unilateral losses. Patients with an acute traumatic cause also should have MRI. A perilymphatic fistula is typically suspected from an inciting event (eg, excessive strain, barotrauma), and testing may be done by using positive pneumatic pressure to evoke eye movements (nystagmus). CT of the temporal bones is usually done to show the bony characteristics of the inner ear and can help elucidate congenital abnormalities (eg, enlarged vestibular aqueduct), fractures of the temporal bone from trauma, or erosive processes (eg, cholesteatoma).
Patients who have risk factors for or symptoms that suggest causes should have appropriate tests based on clinical evaluation (eg, serologic tests for possible HIV infection or syphilis, CBC and coagulation profile for hematologic disorders, ESR and antinuclear antibodies for vasculitis).
Treatment of sudden hearing loss focuses on the causative disorder when known. Fistulas are explored and repaired surgically when bed rest fails to control symptoms.
In viral and idiopathic cases, hearing returns to normal in about 50% of patients and is partially recovered in others.
In patients who recover their hearing, improvement usually occurs within 10 to 14 days.
Recovery from an ototoxic drug varies greatly depending on the drug and its dosage. With some drugs (eg, aspirin, diuretics), hearing loss resolves within 24 h, whereas other drugs (eg, antibiotics, chemotherapy drugs) often cause permanent hearing loss if safe dosages have been exceeded.
For patients with idiopathic loss, many clinicians empirically give a course of glucocorticoids (typically prednisone 80 mg/kg po once/day for 7 to 14 days followed by a 5 day taper). Glucocorticoids can be given orally and/or by transtympanic injection. Direct transtympanic injection avoids the systemic side effects of oral glucocorticoids and appears equally effective except in profound (> 90 decibels) hearing loss. There are data showing that using both oral and intratympanic steroids leads to better outcomes than either alone. Although clinicians often give antiviral drugs effective against herpes simplex (eg, valacyclovir, famciclovir), data show that such drugs do not affect hearing outcomes. There are some limited data suggesting that hyperbaric oxygen therapy may be beneficial in idiopathic sudden hearing loss.