This patient most likely has otosclerosis, a form of conductive hearing loss. Otosclerosis is caused by abnormal bone hardening and growth in the middle ear that disrupts sound transmission from the middle ear to the inner ear. Diagnostic clues in this patient include gradual onset, difficulty hearing low-pitched sounds, and no history of exposure to loud noises. When the Weber test is performed on this patient, the tuning fork is heard more loudly on the left, indicative of conductive hearing loss in the left ear. Treatment of otosclerosis is amplification or surgical stapedectomy, in which a portion of the stapes is removed and replaced with a prosthesis to improve conductive hearing.

Drug-induced hearing loss, a form of sensorineural hearing loss, can be caused by ototoxic medications, including aminoglycosides, chemotherapeutic agents, aspirin, antimalarial agents, and loop diuretics. The dose of aspirin this patient is taking would not be high enough to cause ototoxicity.

Meniere disease is classically a triad of sensorineural hearing loss, tinnitus, and vertigo. This patient does not have either tinnitus or vertigo.

Presbycusis, another form of sensorineural hearing loss, is age-related hearing loss and is typically symmetric and affecting high frequencies. Although this patient is older, his hearing loss is asymmetric and low frequency, which is less consistent with presbycusis.