Sudden Sensorineural Hearing Loss

• Viral-induced cochlear inflammation and hair cell injury: The most widely supported mechanism involves viral infection—particularly cytomegalovirus, herpes simplex virus type 1, varicella-zoster virus, mumps, and coronavirus (including SARS-CoV-2)—leading to direct viral replication within the cochlea or triggering an exaggerated innate immune response. Viral infection activates pattern recognition receptors (TLRs 3, 7, 8, 9) on cochlear epithelial cells and resident immune cells, triggering release of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8) and chemokines that recruit neutrophils and macrophages. This inflammatory cascade causes blood-labyrinth barrier (BLB) disruption—mediated by increased vascular permeability and tight junction dysfunction—leading to perilymphatic edema and increased pressure within the scala tympani. The inflammatory milieu directly damages outer hair cells (OHCs) through oxidative stress mechanisms and inner hair cells (IHCs), with OHC loss predominating in many cases, resulting in the characteristic high-frequency sensorineural hearing loss pattern on audiometry.

• Cochlear ischemia and microvascular thrombosis: Viral and systemic inflammation trigger endothelial dysfunction within the highly vascularized cochlear lateral wall and modiolus. Inflammatory cytokines upregulate tissue factor on endothelial cells and promote a hypercoagulable state, leading to microvascular thrombosis in terminal arterioles supplying the organ of Corti and stria vascularis. The cochlea has minimal collateral circulation and the highest metabolic rate per unit tissue mass in the body, making it exquisitely sensitive to ischemic injury. Ischemia depletes ATP in hair cells and supporting cells, impairing Na+/K+-ATPase function and leading to cellular calcium overload, activation of calpains and caspases, and ultimately apoptotic and necrotic cell death. Additionally, ischemic-reperfusion injury generates reactive oxygen species (ROS) that overwhelm the cochlea's antioxidant defenses (catalase, superoxide dismutase, glutathione peroxidase), perpetuating oxidative damage.

• Autoimmune-mediated cochlear damage: Evidence supports immune-mediated mechanisms in a subset of SSNHL cases, particularly in bilateral presentations or those associated with systemic autoimmune diseases. Cross-reactive antibodies to viral antigens may target heat shock proteins (HSP70) and other autoantigens expressed on cochlear hair cells and supporting cells. Type II hypersensitivity reactions (antibody and complement-mediated) damage the stria vascularis, which is critical for maintaining the 80–100 mV endocochlear potential essential for hair cell transduction. Loss of strial function causes depolarization of inner and outer hair cells, disrupting the ionic gradients required for mechanotransduction and leading to hearing loss. Additionally, T cell-mediated autoimmunity generates inflammatory infiltrates that disrupt cochlear architecture.

• Inner ear membrane rupture and perilymph-endolymph fistula: Traumatic events (barotrauma, temporal bone fractures, explosive noise exposure) or rarely spontaneous rupture of Reissner's membrane (separating endolymph from perilymph) or the oval window membrane creates abnormal communication between the endolymphatic and perilymphatic spaces. This disrupts the crucial ionic composition differences (K+ high in endolymph, Na+ high in perilymph) and allows toxic perilymphatic toxins or endolymphatic potassium to directly contact hair cells, causing acute depolarization and calcium influx leading to cell death. Perilymph leakage may also occur, reducing fluid volume and creating mechanical disruption.

• Genetic susceptibility and ion channel dysfunction: Variants in genes encoding for connexins (GJB2, GJB6), potassium channels (KCNE1, KCNQ1), aquaporin-3, and mitochondrial DNA increase susceptibility to SSNHL, particularly in syndromic and familial cases. These genetic factors impair cellular ion homeostasis, reduce regenerative capacity of cochlear supporting cells, or enhance vulnerability to secondary insults such as inflammation or ischemia.

• Idiopathic SSNHL (most common): Accounts for 70–90% of cases, with viral infection (presumed but unproven in most cases) and viral-triggered immune responses being the leading proposed mechanisms. No specific causative agent is definitively identified in the majority of patients despite serologic and CSF testing, underscoring the limitations of current diagnostic approaches. This category includes suspected viral labyrinthitis and autoimmune SSNHL of unclear etiology.

• Viral etiologies: Direct causative viruses identified through PCR of perilymph (obtained during exploratory tympanotomy), serology, or temporal bone imaging include cytomegalovirus (CMV)—particularly in immunocompromised hosts and congenital infections; herpes simplex virus type 1 (HSV-1)—reactivation in the geniculate ganglion causing Ramsay Hunt syndrome when associated with vesicles in the external auditory canal or soft palate; varicella-zoster virus (VZV)—both primary varicella and zoster reactivation; mumps virus—historically more common before MMR vaccination; measles virus; influenza virus; Epstein-Barr virus (EBV); human immunodeficiency virus (HIV); and emerging SARS-CoV-2 (COVID-19). Viral mechanisms likely operate through both direct cytolysis of infected cochlear cells and immune-mediated bystander destruction.

• Autoimmune and inflammatory disorders: Systemic lupus erythematosus (SLE) presents with SSNHL in 1–24% of patients, mediated by anti-DNA antibodies, anti-SSA/Ro antibodies, and immune complex deposition in the cochlea and membranous labyrinth. Granulomatosis with polyangiitis (GPA, formerly Wegener granulomatosis) causes SSNHL through necrotizing vasculitis affecting cochlear vasculature and stria vascularis; diagnosis is supported by c-ANCA/PR3 positivity and involvement of upper or lower respiratory tract. Polyarteritis nodosa (PAN) causes vasculitic damage to cochlear blood vessels. Behçet disease presents with recurrent oral/genital ulcers and can cause hearing loss through vasculitis. Cogan syndrome—nonsyphilitic interstitial keratitis plus audio-vestibular dysfunction—presents with progressive or sudden SSNHL. Sarcoidosis causes granulomatous inflammation of the cochlea and labyrinth. Relapsing polychondritis involves immune-mediated destruction of cartilage and cochlear structures. Autoimmune inner ear disease (AIED) may present with bilateral progressive or sudden hearing loss.

• Neoplastic causes: Acoustic neuromas (vestibular schwannomas) present with unilateral SSNHL in 50% of cases, typically with concurrent tinnitus and vertigo; distinguished from sudden idiopathic hearing loss by MRI findings of a cerebellopontine angle mass with internal auditory canal involvement and gadolinium enhancement. Leukemias and lymphomas cause SSNHL through direct infiltration of the cochlea, vasculitis, or leukostasis phenomena. Metastatic cancers to the temporal bone or skull base can obstruct cochlear blood supply.

• Vascular and hematologic causes: Cardiovascular disease (myocardial infarction, arrhythmias, heart failure) causes cochlear ischemia through reduced cardiac output and cerebral hypoperfusion. Thrombophilia (including antiphospholipid syndrome, factor V Leiden, prothrombin gene mutation) increases risk of cochlear microvasculature thrombosis. Sickle cell disease causes vaso-occlusive crises affecting the labyrinth. Hyperlipidemia and atherosclerotic disease increase thrombotic risk. Hypercoagulable states associated with malignancy, pregnancy, or oral contraceptive use increase SSNHL incidence.

• Ototoxic medications: Aminoglycoside antibiotics (gentamicin, tobramycin, amikacin)—particularly with renal impairment or prolonged use—accumulate in cochlear hair cells and cause permanent damage through generation of ROS and apoptosis; auditory damage may lag behind vestibular toxicity. Amphotericin B causes cochlear toxicity through generation of ROS and disruption of cochlear blood flow. Chemotherapeutic agents including cisplatin, carboplatin, and doxorubicin cause dose-dependent, irreversible hair cell loss. NSAIDs and acetaminophen increase SSNHL risk, particularly with chronic use. Aspirin (especially high doses) causes reversible hearing loss. Loop diuretics (furosemide, ethacrynic acid) cause acute hearing loss through disruption of strial function and perilymphatic ion composition; ethacrynic acid causes permanent damage while furosemide effects may be reversible. Macrolide antibiotics (azithromycin, erythromycin) rarely cause reversible hearing loss. Methotrexate and tacrolimus have been associated with ototoxicity.

• Temporal bone trauma and barotrauma: Acute traumatic events including explosive noise exposure, motor vehicle accidents, blast injuries, or impact to the temporal bone region cause SSNHL through acoustic trauma (hair cell destruction from excessive vibration), temporal bone fractures (particularly longitudinal fractures with ossicular disruption or perilymph fistula), and perilymph leak through round or oval window rupture. Barotrauma from scuba diving, rapid altitude changes, or forceful Valsalva maneuver can rupture the oval or round window membrane.

• Otologic procedures and surgery: Round window rupture or perilymph fistula may occur spontaneously or result from surgical manipulation, stapes surgery, cochlear implantation, or sudden Valsalva maneuvering. Drilling or instrumentation during mastoid surgery can disrupt ossicular continuity or cause perilymph leak.

• Metabolic and endocrine disorders: Diabetes mellitus increases SSNHL risk through microvascular disease and ischemia. Hypothyroidism has been associated with SSNHL; thyroid hormone influences cochlear development and function. Hyperlipidemia contributes to atherosclerotic cochlear vascular disease. Pregnancy creates a hypercoagulable state increasing thrombotic risk; SSNHL has been reported in association with preeclampsia and placental insufficiency.

• Genetic and syndromic causes: Mitochondrial disorders (including maternally inherited LHON, MELAS, and other mitochondrial cytopathies) present with progressive or sudden SSNHL due to impaired oxidative phosphorylation and ischemic sensitivity. Jervell and Lange-Nielsen syndrome (autosomal recessive long QT with congenital hearing loss) can present with acute decompensation. Alport syndrome causes progressive SSNHL from basement membrane abnormalities in the cochlea. Waardenburg syndrome, Pendred syndrome, and other syndromic hearing loss genes may occasionally present with acute manifestations.

• CNS and infectious disease: Meningitis (bacterial, viral, or tuberculous) causes labyrinthitis ossificans and cochlear inflammation; Neisseria meningitidis and Streptococcus pneumoniae are common bacterial culprits. Syphilis (secondary or tertiary neurosyphilis) causes vasculitis and inflammation affecting the labyrinth; Treponema pallidum invades cochlear vessels and produces Herxheimer reactions. Lyme disease (Borrelia burgdorferi) causes seventh nerve palsy and less commonly SSNHL. Tuberculosis meningitis causes granulomatous infiltration of the cochlea. HIV infection itself causes SSNHL through viral effects and associated opportunistic infections.

• Smoking and substance use: Cigarette smoking increases oxidative stress and cochlear ischemia risk. Cocaine use causes acute vasoconstriction of cochlear vessels. Alcohol abuse impairs cochlear antioxidant defenses.

• Psychogenic factors: A small percentage of sudden hearing loss may be nonorganic (functional), particularly in patients with significant psychiatric comorbidity; distinguishing true SSNHL from nonorganic loss requires careful audiologic testing with reflex testing and imaging to exclude organic pathology.

• Sudden unilateral hearing loss: The cardinal symptom is rapid-onset reduction in auditory acuity occurring over hours to days (defining "sudden" as occurring within 3 days for most definitions, though some extend to 2 weeks). Patients typically report noticing hearing loss upon waking or during a single day, with unilateral presentation in 80–90% of cases. The loss is sensorineural, reflecting cochlear or neural dysfunction rather than conductive pathology. Most commonly, high-frequency hearing loss predominates (3000–8000 Hz), though low-frequency or "cookie-bite" (mid-frequency sparing) patterns occur. The sudden nature distinguishes SSNHL from the insidious progression of age-related hearing loss or occupational noise-induced hearing loss.

• Tinnitus: Reported in 40–80% of SSNHL cases, often concurrent with or preceding the hearing loss by days to weeks. Tinnitus may be unilateral (matching the affected ear) or bilateral and is typically described as high-pitched ringing, roaring, hissing, or buzzing. The mechanism involves increased spontaneous neural activity in the cochlear nucleus and central auditory pathways consequent to loss of normal peripheral input ("deafferentation tinnitus") and possibly active cochlear inflammation generating abnormal signals. Tinnitus may persist even after hearing recovery and significantly impacts quality of life.

• Vertigo and balance dysfunction: Present in 50% of SSNHL cases, ranging from mild dizziness to severe vertigo with nausea and vomiting. Vertigo suggests concurrent vestibular involvement (viral labyrinthitis pattern) and typically occurs acutely or within days of hearing loss onset. Vertigo is distinguished from dizziness by rotatory sensation; postural instability and nystagmus may be present on examination. The presence of vertigo does not necessarily predict poorer hearing prognosis but suggests a more widespread labyrinthine inflammatory process. Severe vertigo typically improves over days to weeks due to central compensation, but some patients experience chronic imbalance and positional vertigo.

• Aural fullness and pressure sensation: Patients often describe a sensation of fullness, pressure, or blockage in the affected ear, sometimes described as "cotton in the ear." This symptom suggests altered fluid dynamics within the labyrinth (endolymphatic hydrops) or perilymphatic edema. Aural fullness may precede the abrupt hearing loss by days and tends to resolve faster than hearing loss itself.

• Hyperacusis or recruitment: Some patients with cochlear (as opposed to retrocochlear) SSNHL experience recruitment—abnormal loudness growth where soft sounds may be inaudible but moderately loud sounds become uncomfortably loud—reflecting outer hair cell loss relative to inner hair cell preservation. This is physiologically explained by loss of the compressive, nonlinear amplification normally provided by OHC electromotility, which reduces the dynamic range of cochlear frequency analysis.

• Otologic examination findings: Otoscopy reveals normal tympanum and external auditory canal (absence

Bedside triage (first step)

• 512 Hz tuning fork tests: the immediate task is separating sensorineural from conductive loss, because conductive causes (cerumen impaction, effusion, tympanic membrane perforation) are benign and treated differently. Weber lateralizes to the unaffected ear and Rinne remains air > bone in the affected ear in SSNHL. Lateralization to the symptomatic ear indicates conductive loss and argues against SSNHL.
• Otoscopy and pneumatic otoscopy: must be normal; visible cerumen, middle-ear fluid, or a perforation redirects the workup entirely.

Confirmatory test

• Pure-tone audiometry: the diagnostic gold standard and the single most important next step. The accepted threshold, reflected in the American Academy of Otolaryngology–Head and Neck Surgery Foundation (AAO-HNSF) Clinical Practice Guideline on Sudden Hearing Loss, is a loss of at least 30 dB across three consecutive frequencies developing within 72 hours, compared with the contralateral ear or with prior audiograms. Bone- and air-conduction thresholds shift together with no air–bone gap.
• Adjunctive audiologic testing: word recognition scores disproportionately poor for the pure-tone average suggest retrocochlear disease; tympanometry is normal (type A); absent or elevated acoustic reflexes with rollover raise concern for an eighth-nerve lesion.

Excluding retrocochlear pathology

• MRI of the internal auditory canals and posterior fossa with gadolinium: recommended by AAO-HNSF to evaluate for vestibular schwannoma, demyelination, or brainstem/cerebellar infarction; auditory brainstem response is an acceptable alternative when MRI cannot be obtained.
• Testing to avoid: AAO-HNSF recommends against routine head CT and against indiscriminate laboratory panels. Targeted testing (e.g., treponemal serology, ANCA, autoimmune studies) is reserved for bilateral, recurrent, or fluctuating disease or when history suggests a specific systemic cause.

First-line therapy

• Systemic corticosteroids: representative agent prednisone, typically 1 mg/kg/day (commonly up to 60 mg daily) for about 7–14 days followed by a taper. Offered as an option by AAO-HNSF (evidence is limited and spontaneous recovery is common). Mechanism: suppression of cochlear cytokine release, restoration of blood–labyrinth barrier integrity, and upregulation of mineralocorticoid-dependent Na+/K+-ATPase in the stria vascularis, supporting the endocochlear potential.
• Intratympanic corticosteroid: dexamethasone or methylprednisolone injected through the tympanic membrane, diffusing across the round window into perilymph. Achieves far higher inner-ear drug levels than oral dosing and is the preferred initial route when systemic steroids are contraindicated — uncontrolled diabetes, active infection, poorly controlled hypertension, glaucoma, prior steroid psychosis, or pregnancy concerns.

Escalation / salvage

• Intratympanic steroid salvage: AAO-HNSF recommends offering salvage injections for incomplete recovery, generally within roughly 2–6 weeks of onset.
• Hyperbaric oxygen therapy: may be offered in combination with steroids within about two weeks of onset, and as salvage within about one month; raises perilymphatic oxygen tension in an ischemia-vulnerable, poorly collateralized cochlea.

Explicitly not recommended

• Routine antivirals, thrombolytics, vasodilators, vasoactive agents, and antioxidants: AAO-HNSF recommends against these — no demonstrated benefit and real harm (bleeding, hypotension).

Definitive/rehabilitative

• Amplification and implantation: mandatory outcome audiogram within about six months. Persistent loss is managed with hearing aids, CROS devices, or cochlear implantation for profound unilateral or bilateral loss. Counseling on the natural history and on unilateral-hearing safety is a guideline-level requirement.

Complications of the disease

• Permanent sensorineural hearing loss: irreversible hair cell and spiral ganglion loss; hair cells do not regenerate in mammals. Signaled by failure of the follow-up audiogram to improve, especially with profound initial loss, downsloping audiogram, advanced age, or accompanying vertigo — the classic poor-prognosis cluster.
• Chronic tinnitus: deafferentation-driven hyperactivity in the cochlear nucleus and auditory cortex; may persist or worsen even after threshold recovery.
• Persistent vestibular hypofunction: labyrinthine involvement produces unilateral caloric weakness with chronic unsteadiness and increased fall risk; a positive head-impulse test toward the affected side is the physical finding.
• Missed vestibular schwannoma: SSNHL may be its presenting event; delayed diagnosis allows brainstem compression. Asymmetric word recognition out of proportion to pure-tone loss is the clue — MRI is what prevents this.
• Missed posterior circulation stroke (emergency): labyrinthine artery infarction from AICA territory can present as sudden hearing loss with vertigo. Any accompanying diplopia, dysarthria, dysmetria, facial numbness, direction-changing nystagmus, or a normal head-impulse test in an acutely vertiginous patient mandates emergent neuroimaging and stroke pathway activation.
• Bilateral or recurrent SSNHL: flags systemic autoimmune disease or vasculitis; missed granulomatosis with polyangiitis or Cogan syndrome risks organ-threatening progression.
• Psychosocial morbidity: depression, social isolation, and impaired sound localization with loss of the head-shadow effect.

Complications of treatment

• Systemic corticosteroids: hyperglycemia (watch closely in diabetics), insomnia, mood lability and frank steroid psychosis, hypertension, gastritis, immunosuppression, and with repeated courses avascular necrosis of the femoral head — hip or groin pain after steroids is the sentinel symptom.
• Intratympanic injection: transient vertigo and pain, otitis media, and persistent tympanic membrane perforation — new conductive loss with a visible perforation on otoscopy.
• Hyperbaric oxygen: middle-ear and sinus barotrauma, reversible myopia, and rarely oxygen-toxicity seizures; contraindicated with untreated pneumothorax (emergency if tension physiology develops).

• The single best next step is an audiogram, not an MRI and not a steroid prescription. Pure-tone audiometry confirms the diagnosis and documents the ≥30 dB loss across three consecutive frequencies within 72 hours; treatment and imaging follow. Stems that offer "start prednisone" before any hearing test are testing sequence.
• Tuning forks separate the two branches of the vignette. Weber lateralizes away from the affected ear in SSNHL. If Weber lateralizes toward the symptomatic ear, think cerumen impaction, effusion, or otosclerosis — the most common distractor built into these stems.
• SSNHL is an otologic emergency with a two-week window. Recovery odds drop with delay, which is why corticosteroids are started empirically while MRI is pending. Reassuring the patient to "return in a month" is always the wrong answer.
• Every unilateral SSNHL needs MRI of the internal auditory canals with gadolinium. The association examiners love is vestibular schwannoma, hinted at by disproportionately poor word recognition, absent acoustic reflexes, or facial numbness (CN V involvement at the cerebellopontine angle).
• Vertigo plus hearing loss plus any central sign is a stroke until proven otherwise. AICA/labyrinthine artery infarction mimics SSNHL; diplopia, dysarthria, ataxia, or a normal head-impulse test in an acutely vertiginous patient sends the patient to emergent neuroimaging, not to the otolaryngology clinic.
• Intratympanic dexamethasone is the answer when systemic steroids are contraindicated (brittle diabetes, prior steroid psychosis) and is also the guideline-endorsed salvage option after incomplete recovery on oral therapy.
• AAO-HNSF recommends against antivirals, thrombolytics, vasodilators, and routine head CT. "Start valacyclovir" is a perennial trap despite the viral hypothesis in the pathophysiology.
• Bilateral simultaneous SSNHL is not idiopathic until proven otherwise — pursue autoimmune, syphilitic, and vasculitic causes.