Presbycusis high-frequency sloping sensorineural hearing loss

A 74-year-old retired schoolteacher presents with a 3-year history of difficulty following conversations in noisy restaurants. His wife reports he turns the television volume very loud and mishears consonants more than vowels. Otoscopy is normal bilaterally. Weber test is central and Rinne shows air conduction > bone conduction bilaterally. Pure tone audiometry is shown in the diagram. The audiometric pattern marked **B** — symmetric bilateral high-frequency downsloping sensorineural hearing loss worst at 4–8 kHz with no air-bone gap — is most consistent with which underlying pathology?