Residency · Residency · Otolaryngology

Sensorineural Hearing Loss: Evaluation and Management

Overview

Sensorineural hearing loss (SNHL) results from dysfunction of the cochlea, auditory nerve, or central auditory pathways. Systematic workup is essential to distinguish cochlear from retrocochlear pathology and to identify treatable causes, including sudden SNHL, which constitutes an otologic emergency.

Classification

By Onset

Congenital: present at birth (genetic, infectious, structural). Acquired: develops after birth (noise, ototoxicity, aging, infection, trauma).

By Timing

Sudden SNHL (SSNHL): >= 30 dB loss over 3 contiguous frequencies within 72 hours. Progressive: gradual worsening over weeks to years. Fluctuating: variable hearing levels (Meniere disease, autoimmune inner ear disease).

By Laterality

Unilateral: must rule out retrocochlear pathology (vestibular schwannoma). Bilateral: more often systemic etiology (presbycusis, ototoxicity, genetic).

By Severity (WHO classification)

Mild: 26-40 dB. Moderate: 41-55 dB. Moderately severe: 56-70 dB. Severe: 71-90 dB. Profound: >90 dB.

Etiology

Cochlear Causes

Presbycusis: most common SNHL; age-related, high-frequency, bilateral, symmetric. Noise-induced: occupational or recreational; 4 kHz notch on audiogram. Ototoxicity: aminoglycosides, cisplatin, loop diuretics, salicylates. Meniere disease: fluctuating low-frequency SNHL with vertigo, tinnitus, aural fullness. Autoimmune inner ear disease (AIED): bilateral, progressive over weeks-months; responds to steroids. Viral labyrinthitis: post-viral SNHL (mumps, measles, CMV, herpes). Perilymph fistula: post-traumatic or post-surgical. Otosclerosis (cochlear): mixed hearing loss with SNHL component. Genetic: connexin 26 (GJB2) most common non-syndromic cause.

Retrocochlear Causes

Vestibular schwannoma (acoustic neuroma): unilateral SNHL, often with poor speech discrimination disproportionate to pure tone loss. Meningioma of the CPA/IAC. Other CPA tumors: epidermoid, arachnoid cyst. Auditory neuropathy spectrum disorder (ANSD): present OAEs, absent or abnormal ABR.

Central Causes

Stroke (AICA territory), Demyelinating disease (MS), Central auditory processing disorder.

Systematic Workup

History

Onset (sudden vs. gradual), duration, laterality. Associated symptoms: vertigo, tinnitus, aural fullness, otorrhea, otalgia. Noise exposure history (occupational and recreational), Medication history (ototoxic drugs), Family history of hearing loss, Head trauma, barotrauma, recent surgery, Autoimmune disease history, History of meningitis, viral infections.

Physical Examination

Otoscopy: normal TM in pure SNHL. Tuning fork tests: Weber lateralizes to the better ear; Rinne positive bilaterally (AC > BC) even in the affected ear. Cranial nerve examination (especially CN V, VII, VIII), Cerebellar testing if retrocochlear concern. Pneumatic otoscopy (fistula test if perilymph fistula suspected).

Audiometric Evaluation

Pure tone audiometry: air and bone conduction thresholds; no significant air-bone gap in SNHL. Speech reception threshold (SRT): should agree with pure tone average (PTA) within 10 dB. Word recognition score (WRS): poor WRS disproportionate to pure tone loss suggests retrocochlear pathology (rollover phenomenon). Tympanometry: Type A (normal) in pure SNHL. Acoustic reflexes: absent or elevated in retrocochlear lesions; reflex decay is abnormal. Otoacoustic emissions (OAE): present = intact outer hair cell function (cochlear); absent = cochlear damage. Auditory brainstem response (ABR): abnormal in retrocochlear pathology; prolonged wave I-III or I-V interpeak latencies; used for threshold estimation in infants.

Imaging

MRI with gadolinium (IAC protocol): gold standard for ruling out vestibular schwannoma. Indications: asymmetric SNHL (>10-15 dB difference at 2 or more frequencies), unilateral tinnitus, unexplained unilateral SNHL. CT temporal bone: if conductive component, congenital anomaly, or trauma suspected. MRI brain: if central pathology suspected.

Laboratory Studies (selected cases)

CBC, ESR, CRP (autoimmune/inflammatory), ANA, RF, anti-dsDNA (autoimmune), RPR/FTA-ABS (syphilis -- reversible cause), TSH (thyroid dysfunction), Lyme titers (in endemic areas), Connexin 26 / genetic testing (congenital/pediatric), Anti-68 kD antibody (heat shock protein -- AIED).

Sudden Sensorineural Hearing Loss (SSNHL)

Definition

>= 30 dB SNHL over at least 3 contiguous frequencies, Occurring within 72 hours, Otologic emergency.

Epidemiology

Incidence: 5-27 per 100,000 per year. Most common in 40-60 year age group, Unilateral in >95% of cases.

Etiology

Idiopathic in 85-90% of cases. Proposed mechanisms: viral (cochlear inflammation), vascular (cochlear ischemia), autoimmune, membrane rupture. Identifiable causes: vestibular schwannoma (1-3%), stroke, perilymph fistula, Meniere disease, autoimmune, ototoxicity, MS.

Workup

Urgent audiogram to confirm and quantify. MRI with gadolinium to exclude retrocochlear pathology (can be done urgently or within 4-6 weeks). Routine labs generally not recommended unless clinical suspicion (AAO-HNS 2019 guidelines).

Treatment (Controversial)

Systemic Corticosteroids (Standard of Care)

Oral prednisone 1 mg/kg/day (max 60 mg) for 10-14 days with taper. Should be initiated as soon as possible (ideally within 2 weeks of onset). Evidence: moderate quality; several trials show benefit over placebo. Contraindications: uncontrolled diabetes, active infection, TB.

Intratympanic Steroids

Primary therapy: for patients who cannot take systemic steroids (diabetes, immunosuppression). Salvage therapy: for patients who fail systemic steroids (AAO-HNS recommends offering within 2-6 weeks of onset). Dexamethasone 10-24 mg/mL or methylprednisolone 40 mg/mL, 3-4 injections over 2 weeks. SSNHL guideline recommends offering IT steroids as salvage when incomplete recovery after initial systemic therapy.

Combination Therapy

Systemic + intratympanic steroids simultaneously. Some studies suggest benefit; others show no significant difference from systemic alone. Currently an area of controversy.

Other Therapies (Not Recommended as Standard)

Antiviral agents: no proven benefit (multiple RCTs). Hyperbaric oxygen: limited evidence; may be considered as adjunct within 2 weeks. Vasodilators, rheologic agents: no proven benefit. Anticoagulants: not recommended.

Prognosis

Spontaneous recovery: ~30-65% (confounds treatment studies). Poor prognostic factors: profound loss, downsloping audiogram, older age, delayed treatment, associated vertigo. Good prognostic factors: low-frequency loss pattern, younger age, early treatment, mild-moderate loss.

Hearing Rehabilitation

Hearing Aids

First-line for mild to moderate SNHL. Behind-the-ear (BTE), receiver-in-canal (RIC), in-the-ear (ITE), completely-in-canal (CIC). Over-the-counter hearing aids now available (FDA 2022), CROS/BiCROS aids for single-sided deafness.

Bone-Anchored Hearing Devices

For single-sided deafness or conductive/mixed loss not amenable to conventional aids. Osseointegrated implant (Baha, Ponto) or passive transcutaneous devices (Osia, Bonebridge).

Cochlear Implants

For severe-profound SNHL with poor word recognition despite optimally fitted hearing aids. See separate seminar on cochlear implantation.

<image>Audiometric comparison showing four classic patterns of sensorineural hearing loss: (1) presbycusis with bilateral symmetric high-frequency downsloping loss, (2) noise-induced hearing loss with a 4 kHz notch and recovery at 8 kHz, (3) Meniere disease with low-frequency hearing loss, and (4) sudden SNHL with a flat moderate-severe unilateral loss. Four-panel audiogram illustration with labeled patterns.</image>

<image>MRI of the internal auditory canal with gadolinium contrast showing a small enhancing vestibular schwannoma in the left IAC. The normal right IAC is shown for comparison. Labeled axial T1-weighted post-contrast image with the tumor, cochlear nerve, facial nerve, and IAC fundus identified.</image>

<image>Flowchart diagram for the systematic evaluation of sensorineural hearing loss. Starting with history and audiometry, branching into unilateral vs bilateral, sudden vs progressive, with decision points for MRI, laboratory workup, and treatment pathways including steroids for SSNHL, hearing aids, and cochlear implant evaluation. Color-coded clinical algorithm.</image>

Clinical Pearls

Any asymmetric SNHL or unilateral tinnitus warrants MRI to rule out vestibular schwannoma. Sudden SNHL is an otologic emergency -- initiate systemic steroids as soon as possible; do not wait for MRI results. Poor word recognition disproportionate to pure tone thresholds suggests retrocochlear pathology. The 4 kHz notch is characteristic of noise-induced hearing loss. Autoimmune inner ear disease should be suspected with bilateral, rapidly progressive SNHL over weeks to months that responds to corticosteroids. Intratympanic steroid salvage therapy should be offered to patients with incomplete recovery from SSNHL after systemic steroids. Always check for syphilis (RPR) in unexplained bilateral SNHL -- it is one of the few reversible causes. Antiviral therapy has no proven benefit in idiopathic SSNHL and should not be routinely prescribed.

References

• 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.
• Rauch SD, Halpin CF, Antonelli PJ, et al. "Oral vs intratympanic corticosteroid therapy for idiopathic sudden sensorineural hearing loss: a randomized trial." JAMA. 2011;305(20):2071-2079.
• Stachler RJ, Chandrasekhar SS, Archer SM, et al. "Clinical Practice Guideline: Sudden Hearing Loss." Otolaryngol Head Neck Surg. 2012;146(3 Suppl):S1-S35.
• Lin FR, Niparko JK, Ferrucci L. "Hearing loss prevalence in the United States." Arch Intern Med. 2011;171(20):1851-1852.

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