Hearing Loss — Conductive vs Sensorineural

Modifiable risk factors (the ones stems reward you for spotting)

• Noise exposure: cumulative dose matters more than any single event; NIOSH sets a recommended exposure limit around 85 dBA over an 8-hour day, and hearing conservation programs are OSHA-mandated in industry. Recreational sources (firearms, power tools, concerts) count.
• Ototoxic drug exposure: aminoglycosides, platinum chemotherapy, and loop diuretics — risk is synergistic when an aminoglycoside and a loop diuretic are given together, and is amplified by renal impairment.
• Cotton-tipped swab use and ear candling: the AAO-HNSF cerumen impaction guideline explicitly advises against both; swabs impact wax deeper and cause perforations.
• Vascular risk factors: smoking, diabetes, and hypertension accelerate cochlear strial and microvascular loss.
• Barotrauma and head trauma, including temporal bone fracture.

Non-modifiable risk factors

• Age: the dominant driver of SNHL; presbycusis is bilateral, symmetric, high-frequency.
• Family history: otosclerosis is autosomal dominant with incomplete penetrance, favors women, and classically worsens during pregnancy.
• Craniofacial/genetic syndromes: Down syndrome, cleft palate, Treacher Collins — eustachian dysfunction drives recurrent CHL.
• Perinatal factors: congenital CMV is the leading nongenetic cause of congenital SNHL; prematurity, NICU stay >5 days, hyperbilirubinemia requiring exchange transfusion, and bacterial meningitis are Joint Committee on Infant Hearing risk indicators. The USPSTF recommends universal newborn hearing screening.

• Cerumen impaction or foreign bodies: Obstruction of the external auditory canal physically prevents sound wave propagation to the tympanic membrane
• Otitis media (acute or chronic): Fluid accumulation in the middle ear space reduces ossicular chain mobility and dampens sound transmission through the middle ear
• Otosclerosis: Abnormal bone remodeling at the oval window (stapedial footplate) causes progressive fixation of the stapes, preventing normal ossicular vibration and sound conduction to the perilymph
• Ossicular chain discontinuity: Trauma, infection, or cholesteatoma can damage the malleus, incus, or stapes, interrupting the mechanical coupling needed for sound amplification
• Tympanic membrane perforation: Loss of membrane integrity eliminates the pressure differential needed to drive ossicular motion and transmit sound efficiently

• Hair cell damage (cochlear): Damage to outer hair cells reduces cochlear amplification via somatic motility; damage to inner hair cells reduces neural transduction; both result in decreased sound detection and frequency discrimination
• Noise-induced hearing loss (NIHL): Exposure to loud sounds (>85 dB) causes mechanical trauma to stereocilia of outer hair cells, beginning at high frequencies (3–6 kHz); cumulative and irreversible
• Age-related presbycusis: Progressive loss of cochlear hair cells and strial atrophy occurs with aging; affects high frequencies first and is bilateral and symmetrical
• Ototoxic medications: Aminoglycosides, cisplatin, loop diuretics, and NSAIDs damage cochlear and vestibular hair cells through oxidative stress and direct cellular toxicity
• Genetic mutations: Mutations in GJB2 (connexin 26) and other genes disrupt intercellular communication and ion homeostasis in the cochlea, causing congenital or progressive SNHL
• Viral infection (sudden SNHL): Viral invasion of the cochlea or autoimmune cochlear damage (possibly post-viral) causes acute hair cell loss and inflammation
• Temporal bone trauma: Transection of the cochlear nerve or direct cochlear damage from temporal bone fractures causes immediate, permanent hearing loss
• Acoustic neuroma (vestibular schwannoma): Benign tumor of CN VIII compresses the auditory portion of the nerve, causing progressive unilateral SNHL, tinnitus, and vertigo

CONDUCTIVE HEARING LOSS

• Conductive-type hearing loss — Patient reports difficulty hearing that improves in noisy environments (paradoxically better in background noise because others must speak louder); the patient's own voice sounds abnormally loud to them (autophony)
• Otoscopic findings vary by etiology: Cerumen impaction shows visible wax; otitis media reveals dull, retracted tympanum ± fluid level or air-fluid interface; otosclerosis shows normal tympanum (diagnosis by imaging/audiometry)
• Congenital CHL — Congenital stapes fixation (otosclerosis) or ossicular malformations present with hearing loss from birth; may be syndromic (e.g., Treacher Collins, branchio-oto-renal syndrome)
• Progressive hearing loss over months to years — Otosclerosis typically presents in 20s–40s with gradual, bilateral (though often asymmetric) hearing loss; more common in women; family history present in ~50%
• Acute presentation — Sudden hearing loss with ear fullness and otalgia suggests acute otitis media; traumatic perforation causes immediate hearing loss with bloody drainage

SENSORINEURAL HEARING LOSS

• High-frequency hearing loss — Noise-induced and presbycusis classically spare low frequencies initially; patients report difficulty understanding speech in noisy environments (opposite of CHL) and tinnitus
• Sudden sensorineural hearing loss (SSHL) — Abrupt onset of unilateral hearing loss (≥30 dB at 3 consecutive frequencies) over <3 days; medical emergency; associated with viral prodrome, vertigo, or tinnitus
• Tinnitus and vertigo — Often accompany SNHL, particularly with acoustic neuroma (unilateral symptoms red flag) or Ménière disease (episodic vertigo, fluctuating hearing, ear fullness)
• Age of onset distinguishes etiologies: Congenital SNHL (birth to early childhood) suggests genetic, intrauterine infection (TORCH), or perinatal hypoxia; adult-onset suggests noise, ototoxins, age, or acquired disease
• Asymmetric or unilateral SNHL — Raises suspicion for retrocochlear pathology (acoustic neuroma) or specific acquired cause; symmetrical bilateral SNHL suggests genetic, age-related, or systemic cause
• Speech discrimination intact in CHL, reduced in SNHL — Patients with SNHL have difficulty understanding even when sound is amplified; classic complaint: "I can hear you but can't understand you"

CLINICAL EXAMINATION

• Rinne test (tuning fork 512 Hz): Air conduction (AC) > bone conduction (BC) = normal; BC > AC = conductive loss; AC = BC or both diminished = sensorineural loss. Performed on forehead (Weber lateralizes to affected ear in conductive loss, away from affected ear in sensorineural loss)
• Weber test: Tuning fork on forehead; sound lateralizes toward the weaker ear in unilateral CHL (paradoxically) or away from ear with SNHL
• Otoscopy: Essential to identify cerumen, tympanic membrane perforation, retraction, fluid level, or signs of otosclerosis (Schwartze sign = reddish hue from vascular otosclerotic focus)

AUDIOMETRY (Gold Standard)

• Pure-tone audiometry: Tests air and bone conduction thresholds across frequencies (125–8000 Hz). CHL shows air-bone gap (AC threshold > BC threshold by ≥15 dB); SNHL shows parallel elevation of AC and BC with little/no gap
• Speech audiometry (discrimination): Patients with normal discrimination score but elevated pure-tone thresholds suggests CHL; poor discrimination despite adequate amplification suggests SNHL
• Tympanometry: Measures middle ear compliance; type A (normal) in SNHL/normal ears; type B (flat, no compliance) in fluid-filled middle ear; type As (shallow) in ossicular fixation (otosclerosis)
• Acoustic reflexes: Present in normal hearing and CHL (unless ossicular chain interrupted); absent in sensorineural loss (confirms cochlear/retrocochlear origin)

IMAGING

• CT temporal bone (high-resolution): First-line for suspected otosclerosis (shows demineralization at oval window); evaluates ossicular chain disruption, cholesteatoma, and temporal bone fracture
• MRI with gadolinium: Indicated for asymmetric SNHL or unilateral symptoms to rule out acoustic neuroma; also useful for retrocochlear pathology and inflammatory conditions
• Audiologic imaging algorithm: CHL + normal CT = consider otosclerosis (may need MRI to assess for retrocochlear involvement); SNHL unilateral = MRI mandatory; SNHL bilateral symmetrical in elderly = likely presbycusis (imaging not needed unless red flags)

LABORATORY/ADDITIONAL TESTING

• Auditory brainstem response (ABR): Electrophysiologic test useful in patients unable to cooperate with audiometry (infants, altered mental status) or to detect retrocochlear

Immediate/urgent action

• Sudden sensorineural hearing loss is a time-critical diagnosis. The AAO-HNSF sudden hearing loss guideline directs clinicians to distinguish SSNHL from conductive loss, confirm with audiometry, and offer systemic corticosteroids (representative agent: oral prednisone) as initial therapy within about 2 weeks of onset — earlier is better, because the window for recovering hair cell and stria function is short.
• Intracranial or bony complications of ear infection (mastoiditis, facial palsy, meningeal signs) require emergent imaging, IV antibiotics, and otolaryngology consultation.

First-line therapy by mechanism

• Cerumen impaction: cerumenolytic agents, irrigation, or manual removal under direct visualization (AAO-HNSF).
• Acute otitis media: the AAP recommends high-dose amoxicillin, or amoxicillin-clavulanate if there has been recent beta-lactam exposure or treatment failure; observation is an option in selected older children.
• Otitis media with effusion: the AAO-HNSF guideline recommends watchful waiting and explicitly recommends against antibiotics, antihistamines, decongestants, or intranasal/systemic steroids as treatment of the effusion.

Escalation/second-line

• Intratympanic corticosteroid salvage for SSNHL that fails or incompletely responds to systemic steroids, offered within roughly 2–6 weeks of onset (AAO-HNSF). Hyperbaric oxygen is an option as an adjunct early in the course.
• Amplification: hearing aids for most stable SNHL and for CHL not amenable to surgery; bone-conduction/bone-anchored devices for canal atresia, chronic draining ears, or single-sided deafness.

Definitive/surgical

• Stapedotomy or stapedectomy with prosthesis for otosclerosis; tympanoplasty/ossiculoplasty for perforation or ossicular discontinuity; tympanostomy tubes for persistent bilateral effusion with hearing loss (AAO-HNSF tympanostomy tube guideline); mastoidectomy for cholesteatoma, which is never medically curable.
• Cochlear implantation for bilateral moderate-to-profound SNHL with inadequate benefit from appropriately fitted hearing aids.

Avoid

• Routine antivirals, thrombolytics, vasodilators, or routine head CT in SSNHL (AAO-HNSF recommends against these).
• Concurrent aminoglycoside plus loop diuretic when avoidable.
• Irrigation of the canal when perforation, tube, or infection is suspected.

Complications of untreated hearing loss

• Speech and language delay: unrecognized congenital or early-childhood loss deprives the auditory cortex of input during the critical period; the signal is a child who fails newborn screening or has delayed babbling/vocabulary — this is why JCIH endorses screening by 1 month, diagnosis by 3 months, intervention by 6 months.
• Social isolation, depression, and accelerated cognitive decline: reduced auditory input increases listening effort and withdrawal; hearing loss is recognized as a modifiable risk factor for dementia in later life.
• Falls and injury in older adults, from combined auditory and vestibular degeneration.

Complications of the underlying disease

• Cholesteatoma: keratin debris expands and erodes bone — signals include foul-smelling otorrhea, a retraction pocket or attic crust, new vertigo (labyrinthine fistula), or facial nerve palsy. Erosion into the mastoid or intracranially causing meningitis, epidural abscess, or lateral sinus thrombosis is an emergency.
• Acute mastoiditis: postauricular erythema, tenderness, and a protruding auricle — emergency.
• Necrotizing (malignant) otitis externa in diabetics or immunocompromised patients: Pseudomonas aeruginosa, granulation tissue at the bony-cartilaginous junction, cranial neuropathies — emergency.
• Vestibular schwannoma growth: brainstem compression and obstructive hydrocephalus; headache, ataxia, or altered mental status are late red flags.
• Permanent ototoxic injury: aminoglycoside and cisplatin damage begins at high frequencies and is irreversible; loop diuretic ototoxicity is more often reversible.

Complications of treatment

• Stapes surgery: profound dead ear from inner ear trauma, vertigo, perilymph fistula, dysgeusia from chorda tympani injury, and facial nerve injury.
• Tympanostomy tubes: persistent perforation, tympanosclerosis, otorrhea.
• Intratympanic steroids: transient vertigo, pain, persistent perforation.
• Systemic corticosteroids: hyperglycemia, insomnia, mood change, avascular necrosis with repeated courses.
• Cochlear implantation: increased pneumococcal meningitis risk — ACIP recommends pneumococcal vaccination for implant candidates and recipients; also facial nerve stimulation and device infection.

• **Weber lateralizes to the bad ear in conductive loss and away from the bad ear in sensorineural loss.** Mechanism: a conductive block removes competing ambient air-conducted noise, so bone-conducted sound is perceived as louder on that side. Rinne is BC > AC ("negative Rinne") only in CHL.
• Unilateral or asymmetric SNHL demands MRI with gadolinium of the internal auditory canals to exclude vestibular schwannoma — the single most commonly tested "best next step" after audiometry. A distractor answer will offer CT temporal bone; CT is for bone (otosclerosis, cholesteatoma, fracture), not for nerve.
• Sudden SNHL = urgent oral corticosteroids, per the AAO-HNSF sudden hearing loss guideline. The classic trap is a stem where the tuning forks actually show a conductive pattern — that patient has cerumen or effusion, not SSNHL, and needs otoscopy, not steroids. AAO-HNSF also recommends against routine head CT, antivirals, and vasodilators.
• Otosclerosis buzzwords: young to middle-aged woman, worsening in pregnancy, positive family history, normal-appearing tympanic membrane, Schwartze sign, paracusis of Willis (hears better in noise), type As tympanogram, and the Carhart notch — a dip in bone conduction thresholds around 2000 Hz. Treatment is stapedotomy or a hearing aid.
• Noise-induced hearing loss produces a notch at 4000 Hz that later widens; presbycusis produces bilateral symmetric downsloping high-frequency loss with disproportionately poor speech discrimination.
• Aminoglycoside plus loop diuretic is the classic synergistic ototoxic pair; cisplatin ototoxicity is dose-dependent and permanent.
• Congenital associations to memorize: *GJB2*/connexin 26 for nonsyndromic genetic SNHL; congenital CMV as the leading infectious cause; Alport, Pendred, Usher, and Jervell–Lange-Nielsen (with long QT) as syndromic hits.
• A child with persistent bilateral middle ear effusion and hearing difficulty gets tympanostomy tubes — not antibiotics, antihistamines, or steroids, which the AAO-HNSF otitis media with effusion guideline recommends against.