Hearing Loss: What Could Be Causing It

The Three Types of Hearing Loss

Hearing loss falls into conductive, sensorineural, or mixed categories based on where in the auditory pathway the problem occurs. Identifying which type you have determines every subsequent diagnostic and treatment decision.

Conductive hearing loss results from anything that blocks sound transmission through the outer ear canal, tympanic membrane, or ossicular chain. Common culprits include cerumen impaction, middle ear effusion, tympanic membrane perforation, and otosclerosis. These causes are often reversible with medical or surgical intervention.

Sensorineural hearing loss (SNHL) involves damage to the cochlear hair cells, stria vascularis, or the auditory nerve itself. Once hair cells die, they do not regenerate in humans. A systematic review in The Lancet estimated that age-related SNHL affects 25% of people aged 60-69 and over 50% of those older than 80 1. The distinction matters because SNHL rarely responds to surgery. Amplification or cochlear implantation becomes the primary management pathway.

Mixed hearing loss combines elements of both. A patient with presbycusis who also develops chronic otitis media, for example, has a mixed pattern on audiometry. Treatment must address each component separately.

Age-Related Hearing Loss (Presbycusis)

Presbycusis is the single most common cause of hearing loss in adults over 50, typically presenting as bilateral, symmetric, high-frequency SNHL that progresses over years. The patient notices difficulty understanding speech in noisy environments before they notice quiet-room deficits.

The Baltimore Longitudinal Study of Aging demonstrated that men lose hearing sensitivity approximately 1 dB per year faster than women starting in their 40s, with the 4-8 kHz range affected earliest 2. Pathologically, presbycusis involves loss of outer hair cells in the basal turn of the cochlea, atrophy of the stria vascularis, and degeneration of spiral ganglion neurons.

Risk factors that accelerate presbycusis include diabetes, cardiovascular disease, smoking, and chronic noise exposure. The Beaver Dam Offspring Study (N=3,285) found that smokers had a 1.69 odds ratio for hearing loss compared to nonsmokers after adjusting for age and noise history 3. Managing metabolic and vascular risk may slow progression, though no pharmacologic agent has demonstrated reversal.

The American Academy of Audiology recommends baseline audiometry at age 50, with follow-up every three years for those with normal results and annually for those with established loss.

Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) is the second leading cause of SNHL and the most preventable. It produces a characteristic 4 kHz "notch" on audiometry before spreading to adjacent frequencies.

The National Institute for Occupational Safety and Health (NIOSH) sets the recommended exposure limit at 85 dBA for an 8-hour time-weighted average, with a 3 dB exchange rate. Every 3 dB increase halves the safe exposure duration. A rock concert at 110 dB permits only 1.5 minutes of unprotected exposure before risking permanent damage 4.

NIHL occurs through two mechanisms. Acute acoustic trauma (explosions, gunshots) can rupture the tympanic membrane or dislocate ossicles, producing immediate conductive or mixed loss. Chronic exposure causes metabolic exhaustion and oxidative stress in outer hair cells, leading to gradual SNHL that patients often attribute to "normal aging."

The WHO estimated in 2022 that 1.1 billion young people aged 12-35 are at risk from recreational noise exposure, primarily from personal listening devices and entertainment venues 5. Once established, NIHL is permanent. Management centers on hearing protection, audiometric monitoring, and amplification when indicated.

Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss (SSNHL) is defined as a decline of 30 dB or greater across three consecutive frequencies occurring within 72 hours. It affects 5-27 per 100,000 people annually and constitutes an otologic emergency.

The American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) clinical practice guideline recommends offering systemic corticosteroids within 14 days of onset, with intratympanic steroids as salvage therapy for incomplete recovery 6. The guideline specifies that MRI of the internal auditory canals should be obtained to exclude retrocochlear pathology, particularly vestibular schwannoma (acoustic neuroma), which is found in 1-3% of SSNHL cases.

Dr. Steven Rauch, professor of otolaryngology at Harvard Medical School, has stated: "The biggest mistake in sudden hearing loss is delay. Patients who present within the first week have significantly better outcomes than those who wait."

Prognosis depends on severity at presentation. Patients with mild initial loss (30-50 dB) recover fully in approximately 65% of cases. Those with profound loss (>90 dB) recover fully in fewer than 25%. Viral cochleitis, vascular occlusion, and autoimmune inner ear disease are the leading suspected etiologies, though most cases remain idiopathic.

Otosclerosis and Middle Ear Causes

Otosclerosis involves abnormal bone remodeling at the oval window, progressively fixing the stapes footplate and producing conductive hearing loss. It affects women twice as often as men and typically presents between ages 20 and 40.

The Framingham Cohort identified clinical otosclerosis in 2.5% of Caucasian adults, with histologic evidence of otosclerotic foci in up to 10% of temporal bones at autopsy 7. The condition is bilateral in 70-80% of patients but often asymmetric.

Stapedectomy or stapedotomy closes the air-bone gap in over 90% of surgical cases, with a 1-2% risk of profound SNHL. For patients who decline surgery or have surgical contraindications, hearing aids provide effective amplification. Sodium fluoride was historically used to slow otosclerotic progression, but a 2016 Cochrane review found insufficient evidence to support its routine use 8.

Other conductive causes include:

• Chronic otitis media with tympanic membrane perforation or cholesteatoma
• Ossicular chain discontinuity from trauma or erosion
• Superior semicircular canal dehiscence, which produces autophony and a characteristic low-frequency air-bone gap
• Eustachian tube dysfunction with serous effusion

Ototoxic Medications

More than 200 medications carry ototoxic potential. The most clinically significant are aminoglycoside antibiotics, platinum-based chemotherapeutics, loop diuretics, and high-dose aspirin.

Cisplatin produces bilateral, high-frequency SNHL in 40-80% of treated patients, depending on cumulative dose 9. The damage is dose-dependent and typically irreversible. The FDA approved sodium thiosulfate (Pedmark) in 2022 for reducing cisplatin-induced ototoxicity in pediatric patients with localized, non-metastatic solid tumors 10.

Aminoglycosides (gentamicin, tobramycin, amikacin) damage vestibular and cochlear hair cells through mitochondrial oxidative stress. Gentamicin is preferentially vestibulotoxic, while amikacin is preferentially cochleotoxic. Serial audiometry during treatment allows early detection before symptomatic loss develops.

According to the American Speech-Language-Hearing Association (ASHA) position statement: "Audiologic monitoring should be conducted before, during, and after administration of known ototoxic agents to support early identification and intervention."

Loop diuretics (furosemide, bumetanide) cause transient hearing loss by disrupting the endocochlear potential. The effect is usually reversible upon drug discontinuation but can become permanent with high-dose IV administration, particularly in patients with concurrent renal insufficiency.

Autoimmune and Inflammatory Causes

Autoimmune inner ear disease (AIED) accounts for fewer than 1% of all SNHL cases but is one of the few forms that may respond to immunosuppressive therapy. It typically presents as bilateral, fluctuating or rapidly progressive SNHL over weeks to months.

The diagnosis is clinical. No single biomarker is definitive. Anti-68 kD (anti-HSP70) antibody testing has a sensitivity of approximately 42% and specificity of 90%, making it useful when positive but unreliable when negative 11. A trial of systemic corticosteroids (prednisone 1 mg/kg/day for 4 weeks) serves as both diagnostic and therapeutic: improvement confirms the diagnosis.

Systemic autoimmune conditions associated with hearing loss include:

• Granulomatosis with polyangiitis (Wegener's): hearing loss in 35-50% of patients
• Cogan syndrome: interstitial keratitis with audiovestibular dysfunction
• Systemic lupus erythematosus: SNHL prevalence 6-70% depending on study criteria
• Relapsing polychondritis: auricular and inner ear inflammation

Methotrexate, cyclophosphamide, and biologic agents (rituximab, infliximab) have been used as steroid-sparing agents, though evidence comes primarily from case series rather than randomized trials.

Genetic and Congenital Hearing Loss

Genetic factors cause 50-60% of congenital hearing loss. Over 120 genes are implicated, with mutations in GJB2 (encoding connexin 26) representing the single most common cause of autosomal recessive nonsyndromic SNHL in many populations 12.

Syndromic hearing loss accounts for roughly 30% of genetic cases. The most frequently encountered syndromes include:

• Pendred syndrome (SLC26A4 mutations): SNHL with enlarged vestibular aqueduct and thyroid goiter
• Usher syndrome: SNHL with retinitis pigmentosa, the leading cause of deaf-blindness
• Waardenburg syndrome: SNHL with pigmentary anomalies
• Branchio-oto-renal syndrome: conductive, sensorineural, or mixed loss with branchial and renal anomalies

Universal newborn hearing screening, mandated in all 50 US states, detects congenital loss at a median age of 2-3 months. The Joint Committee on Infant Hearing recommends the "1-3-6" benchmark: screening by 1 month, diagnosis by 3 months, and intervention by 6 months of age 13. Early amplification or cochlear implantation before 12 months of age produces significantly better speech and language outcomes than later intervention.

Retrocochlear Pathology

Vestibular schwannoma (acoustic neuroma) is the prototypical retrocochlear cause. These benign tumors arise from Schwann cells of the vestibular portion of CN VIII within the cerebellopontine angle. Unilateral or asymmetric SNHL is the presenting symptom in over 90% of cases.

The incidence is approximately 1-2 per 100,000 per year, with a mean age at diagnosis of 50. MRI with gadolinium is the gold-standard imaging study, detecting tumors as small as 2-3 mm. Auditory brainstem response (ABR) testing has a sensitivity of 90-95% for tumors larger than 1 cm but misses smaller lesions 14.

Management options include observation with serial MRI (for small, slow-growing tumors), microsurgical resection, and stereotactic radiosurgery (Gamma Knife). The AAO-HNS consensus statement recommends that any patient with unexplained asymmetric SNHL (interaural threshold difference >15 dB at two or more frequencies, or >20 dB at one frequency) undergo MRI evaluation.

Diagnostic Approach

A systematic evaluation begins with history, otoscopy, and audiometry. The Weber and Rinne tuning fork tests provide bedside lateralization but cannot replace formal audiometry.

Pure-tone audiometry quantifies hearing thresholds at 250-8000 Hz by air and bone conduction. The air-bone gap distinguishes conductive from sensorineural loss. Speech discrimination testing (word recognition scores) differentiates cochlear from retrocochlear SNHL: scores disproportionately poor relative to pure-tone thresholds suggest neural pathology.

Tympanometry evaluates middle ear compliance. A flat (Type B) tympanogram indicates effusion or perforation. A peaked but shifted (Type As) pattern suggests ossicular fixation. Otoacoustic emissions (OAEs) test outer hair cell function directly and are absent in SNHL exceeding 30-40 dB.

Additional studies ordered based on clinical suspicion:

• MRI with gadolinium: asymmetric SNHL or suspected retrocochlear lesion
• CT temporal bones: conductive loss, cholesteatoma, superior canal dehiscence
• Serologic testing: RPR/FTA-ABS (syphilis), ESR/CRP (inflammation), thyroid panel, CBC
• Genetic testing: bilateral congenital SNHL, family history, syndromic features

Treatment Options by Type

Treatment matches pathology. Conductive losses are often correctable. Sensorineural losses are managed rather than cured.

For conductive hearing loss: Cerumen removal restores hearing immediately in impaction cases. Myringotomy with tube placement treats chronic serous effusion. Tympanoplasty repairs perforations with a success rate exceeding 85%. Stapedectomy is definitive for otosclerosis. Bone-anchored hearing aids (BAHA) bypass the conductive mechanism entirely for patients who cannot undergo reconstructive surgery.

For sensorineural hearing loss: Hearing aids remain first-line. A Cochrane review of 5 RCTs (N=825) found that hearing aids significantly improve hearing-specific health-related quality of life, listening ability, and general health-related quality of life in adults with mild-to-moderate loss 15. Cochlear implantation is indicated for severe-to-profound bilateral SNHL with limited benefit from aids (open-set sentence recognition <50% in the best-aided condition). Over-the-counter hearing aids, available in the US since October 2022 following FDA final rule, provide an accessible option for perceived mild-to-moderate loss in adults 18 and older.

For sudden SNHL: Oral prednisone (60 mg daily for 14 days with taper) or intratympanic dexamethasone (10 mg/mL, 3-4 injections over 2 weeks). Hyperbaric oxygen therapy may provide additional benefit when combined with steroids, according to a 2012 Cochrane review, though evidence quality is low 16.

When to Seek Urgent Evaluation

Sudden unilateral hearing loss demands evaluation within 24-72 hours. Corticosteroid efficacy diminishes substantially beyond 2 weeks from onset. Other red flags requiring prompt referral include hearing loss with facial weakness (suggesting cholesteatoma or temporal bone pathology), pulsatile tinnitus (suggesting vascular anomaly), and otorrhea that persists beyond 2 weeks despite appropriate treatment.

For adults with gradual bilateral loss, the USPSTF concluded in 2021 that current evidence is insufficient to recommend for or against screening in asymptomatic adults 50 and older (I statement), though the recommendation acknowledged that screening tools are accurate and treatment with hearing aids is effective 17. Primary care physicians should ask about hearing difficulty at annual wellness visits and refer for audiometry when patients report functional impairment.