A case of normal ENG findings on air caloric stimulus that were not substantiated by water stimulus. (Vestibulology Clinic).

A 27-year-old woman came to the office with a 3-month history of dizziness, which had begun immediately following a vacation. The patient had flown home from the vacation without difficulty. It had been her habit to take diphenhydramine when flying and during other motion activities ever since she first experienced motion intolerance during childhood. She was not able to read while in a moving automobile.

She described her dizziness as a rocking feeling that had been present almost constantly since its onset. On occasion she would feel better for a day, but the improvement was not sustained. Her symptoms were most severe while she was walking or standing. She did not experience symptoms while she was lying down, but she did while seated. Gaze to the right or left could intensify the rocking feeling. She said she had experienced approximately 10 of these spells since the onset of her symptoms. She had gained no benefit from the use of meclizine, diazepam, or a scopolamine patch. She had no hearing loss, tinnitus, or aural fullness.

Two months earlier, the patient had undergone electronystagmography (ENG) administered at another office, and her results were reported as normal. Tracings of the caloric responses were not available for perusal, but she indicated that the caloric examination had been performed with an air stimulus.

On physical examination, the patient had difficulty performing the sharpened tandem Romberg test with either foot forward. She also had tenderness over both nuchal areas, more so on the right. Contrast-enhanced magnetic resonance imaging was negative for abnormalities.

Follow-up ENG with a closed-loop water caloric stimulator revealed low-velocity responses to warm stimuli in both ears and to the cool stimulus in the left ear (figures). The patient had a reduced vestibular response left of 45% and a directional preponderance left of 45%. These findings pointed to a peripheral vestibular disorder.

The difference in the caloric responses between the first and second ENG studies reflects the difference between a water-based caloric stimulus and an air-based stimulus. When air caloric stimulators became available in the mid-1970s, the American Neurotology Society examined the results. The air caloric was deemed to be less reliable than water-based stimuli. For example, in a perforated wet ear, warm air can cause the moisture to evaporate, thus cooling the inner ear and producing nystagmus in the opposite direction. Because the air stimulus is so easy to administer, ill-informed consumers have demanded it and manufacturers have responded by continuing to market it. In the case described here, the original ENG findings might have led a physician to misdiagnose the patient as having psychogenic dizziness.

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