Electronystagmography in a patient who could not drive more than 5 minutes at highway speeds. (Vestibulology Clinic).

A 24-year-old man came to the office with a 2-month history of dizziness. He said that while driving his car, he would feel as though he were on a roller coaster and that "the world was going down." To overcome his difficulty in controlling his car, he felt a constant need to turn the steering wheel. At the same time, he was aware of palpitations. Occasionally, he would pull off the road in hopes that the feeling would pass, but 5 minutes after he resumed driving, the problem would recur. He also noted that he experienced fewer problems when he droves slowly rather than at highway speeds.

Since the onset of these symptoms, he also had noted that when he walked, he tended to veer to the right, and while sitting, he occasionally felt as thought the room were moving for a brief period of time. He also reported a family history of dizziness and hearing loss. He had no subjective hearing loss or tinnitus. His problems had failed to respond to meclizine, but he had obtained some slight relief from alprazolam.

The patient had difficulty performing the sharpened tandem Romberg test with the right foot forward. Electronystagmography detected no spontaneous, positional, or neck-torsion nystagmus. Ocular fixation suppression of calorically induced nystagmus was present. The alternate binaural bithermal caloric test induced no response to warm stimulation in the right ear and some reduced response to warm stimulation in the left. According to Jongkees' formula, these stimuli produced an 8% reduced vestibular response (RVR) left and a 33% directional preponderance left. The simultaneous binaural bithermal stimulus induced a type 2 response, which is an RVR coming from the right. Although the induced nystagmus was not robust, it was sufficient to reflect the findings of the warm-water caloric test, as well as his increased difficulty in performing the sharpened tandem Romberg test with the right foot forward.

In this case, each of the caloric responses needed to be examined rather than relying solely on Jongkees' formula, which can be misleading in identifying an RYR. This patient's symptoms are not unusual in a small subset of patients who have peripheral vestibular disorders. While the patient had been driving, the mismatched information coming from the peripheral labyrinths was exaggerated by the speed of the automobile and by a mismatch of the visual and vestibular inputs at that speed. Symptoms manifest when the speed reaches a certain rate. The relief that the patient experienced from alprazolam was related to the drug's suppression of the central processing of these mismatches; alprazolam also suppresses eventual central compensation. His other symptoms-- tending to veer to the right and momentary dizziness-- were not serious enough to have prompted him to seek medical evaluation.