Horizontal canal benign paroxysmal positioning vertigo (h-BPPV): transition of canalolithiasis to cupulolithiasis.

We report on 2 patients with typical features of horizontal canal benign paroxysmal positioning vertigo (h-BPPV). A vigorous head positioning in these patients from supine to a bending-over, head-on-the-knees position reversed the direction of nystagmus from geotropic initially to ageotropic when rolling the head from side to side while supine. We explain this by a conversion of canalolithiasis into cupulolithiasis and conclude that (1) canalolithiasis and cupulolithiasis may sequentially occur in the same semicircular canal with subsequent positioning maneuvers and (2) positional nystagmus beating toward the uppermost ear is not a pathognomonic sign of central vestibular disturbance but can indicate occasional cupulolithiasis.