A 52-year-old man from rural Maharashtra presents with progressive bilateral hearing loss over 8 years. He reports difficulty hearing high-pitched sounds initially, which has now progressed to affect all frequencies. On examination, Weber test shows lateralization to the right ear, and Rinne test reveals bone conduction better than air conduction bilaterally. Otoscopy is normal. Audiometry shows a bilateral high-frequency sensorineural hearing loss with an air-bone gap of 2 dB. Which of the following is the most likely diagnosis?