A 52-year-old man from Delhi presents with progressive bilateral hearing loss over 6 months. He reports tinnitus and occasional vertigo. On examination, Weber test shows lateralization to the right ear, and Rinne test demonstrates bone conduction better than air conduction bilaterally. Otoscopy reveals normal tympanic membranes. Pure tone audiometry shows air-bone gap of 35 dB at 2 kHz. What is the most likely diagnosis?