Strong positional nystagmus in an unexpected direction.

A 53-year-old man presented with a 7-month history of dizziness. He said that while he was putting on a shoe one morning, he experienced a sudden onset of rotary vertigo, nausea, and vomiting. The vertigo subsided at the end of the day, but he was not able to walk alone for 1 week, and he was still very unsteady. He said that when he lies down and looks up, "everything spins" for 15 seconds; whenever he looks up at other times, he experiences a feeling of spinning. When he awakens in the morning, he feels dizzy. He had not been able to work for 10 weeks, and he was unable to drive because he cannot make quick moves.

The patient had no history of hearing loss, tinnitus, or aural fullness. He was taking hydrochlorothiazide and enalapril for hypertension. The only abnormality noted on physical examination was difficulty performing the sharpened tandem Romberg test.

Electronystagmography (ENG) revealed a marked direction-fixed left-beating nystagmus. The nystagmus in the 30[degrees] supine position was 8[degrees]/sec before caloric testing and 15[degrees]/ sec after caloric testing. This difference indicates that a dynamic change took place in the vestibular system during the course of the ENG evaluation. Ordinarily, the vestibular system is stable during testing, which makes calculation possible. However, the significant difference in this case meant that all of the responses induced by the alternate binaural bithermal test were only estimates and could not be used in making any precise calculation. All of this patient's alternate binaural bithermal caloric responses were left-beating.

In something of an interpretive stretch, the nystagmus during cool caloric testing on the right was slightly greater than the highest level of pre-existing nystagmus, which suggests caloric vestibular function in the right ear. The simultaneous binaural bithermal test elicited a similar cool response in the right ear alone at 30[degrees]C. The warm simultaneous binaural bithermal test elicited the only right-beating nystagmus registered during the course of testing. These findings represent a type 2 reduced vestibular response on the left. The introduction of ice water into the left ear, which would be expected to produce a right-beating nystagmus, failed to produce any significant change.

This case provides some clinical insights. First, the vestibular disorder was peripheral and emanating from the left ear. Second, a direction-fixed left-beating nystagmus would be expected to indicate a right-sided abnormality. Third, the simultaneous binaural bithermal test correctly showed that the left ear was the source of the dizziness. Finally, the ice water in the left ear indirectly corroborated the left ear as the hypoactive ear.

>From Neurotolgic Associates, P. C., New York City.