presbycusis

**Definition:** Age-related sensorineural hearing loss (SNHL), usually bilateral and symmetric, gradually progressive, and affecting high frequencies first.

**Pathophysiology:** - Loss of cochlear hair cells (especially outer hair cells) at the basal turn, which encodes high frequencies. This is why high frequencies are lost first. - Contributing factors: cumulative noise exposure, oxidative stress and mitochondrial damage, atrophy of the stria vascularis (metabolic presbycusis), spiral ganglion neuron loss (neural presbycusis), and reduced basilar membrane compliance (cochlear conductive presbycusis). - Risk factors: older age, male sex, genetics, smoking, diabetes, hypertension and atherosclerosis, ototoxic drugs (aminoglycosides, loop diuretics, cisplatin, salicylates), and chronic noise exposure. - Hair cells do not regenerate in humans, so the loss is permanent.

**Clinical features:** - Gradual, bilateral hearing loss, typically after age 60. - Difficulty understanding speech, especially in noisy settings (the "cocktail party" problem). Consonants (s, f, th, k) are lost first, so patients say "I can hear but can't understand." - Poor speech discrimination out of proportion to pure-tone loss, along with loudness recruitment. - Tinnitus is common.

**Diagnosis:** - Weber: no lateralization (symmetric loss). - Rinne: air conduction > bone conduction bilaterally (normal pattern, as in all SNHL). - Audiometry: bilateral symmetric high-frequency SNHL with a sloping downward audiogram. Speech discrimination scores are reduced. - Asymmetric hearing loss should prompt evaluation for a retrocochlear lesion (vestibular schwannoma) with MRI.

**Management:** - Hearing aids are first-line. - Cochlear implants for severe to profound loss. - Assistive listening devices, communication strategies, and avoidance of noise and ototoxins. - Untreated hearing loss is associated with social isolation, depression, and cognitive decline or dementia.

**Differentiating high-yield points:** - Noise-induced hearing loss: a notch at 4000 Hz on audiogram. - Otosclerosis: conductive loss with a normal tympanic membrane, a negative Rinne (BC > AC), and a Carhart notch at 2000 Hz. - Ménière disease: episodic vertigo, tinnitus, aural fullness, and low-frequency fluctuating SNHL. - Vestibular schwannoma: unilateral SNHL and tinnitus, with bilateral tumors in NF2. - Sudden SNHL: loss over <72 hours, treated with urgent steroids.