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A 52-year-old man presents with sudden unilateral hearing loss. While watching television the day before, he noted an abrupt decrease in hearing in his left ear. This was associated with a feeling of pressure and fullness in the ear and an intermittent sensation of “buzzing or ringing.” The hearing deficit was confirmed when he tried to use the telephone: the sound he perceived through the affected ear was markedly diminished and distorted. He attempted to clean his ear canal, but this did not help—nor was there any improvement the next morning.
The patient is otherwise healthy. He uses NSAIDs occasionally for musculoskeletal pain. He takes no other medications. He reports that he has had several episodes of mild vertigo in the past 24 hours, roughly concurrent with his ear symptoms.
Vital signs are normal. Examination of the ears reveals a patent left ear canal and a readily visible and normal-appearing tympanic membrane. Cranial nerves II through XII are normal except for significant loss of hearing in the left ear; bedside tests suggest that the hearing loss is sensorineural rather than conduction-related. Extraocular movements are intact, and there is no nystagmus. The remainder of the physical findings, including the results of a detailed neurological examination, are normal.
Results of initial laboratory studies, including a complete blood cell count, biochemistry profile, and measurement of blood glucose and cholesterol levels, are normal.
Which of the following is the most likely diagnosis?