Vertical Nystagmus in Routine Caloric Testing

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Abstract
Vertical nystagmus may occur in caloric testing when only horizontal is expected. We examined this occurrence in 112 normal subjects and in 339 patients with dizziness. Vertical nystagmus was found in 29 percent of normals and in 12 percent of patients with dizziness, more often with hot than cool caloric stimuli and it is always accompanied by horizontal nystagmus. The finding occurred with peripheral and central nervous system diagnoses as well as with patients whose dizziness was considered psychogenic or was undiagnosed. Maximum slow component velocity (SCV) of vertical nystagmus was usually half or less than that of the nystagmus in the horizontal lead. The SCV time profiles of the nystagmus in horizontal and vertical leads differed considerably. Possible origins of vertical nystagmus are discussed. Whatever the origin, it is clear that the finding of vertical nystagmus in routine caloric testing does not automatically denote disease of the central nervous system.