A 38-year-old woman with a 2-week history of sudden hearing loss in the left ear presents to the clinic. Otoscopy is normal. Weber test lateralizes to the right ear. Rinne test shows bone conduction > air conduction on the left. Pure tone audiometry confirms unilateral sensorineural hearing loss (SNHL) with threshold of 45 dB. She denies vertigo or tinnitus. What is the most appropriate immediate next step?