[Horizontal canal benign paroxysmal positional vertigo (HC-BPPV) with direction-changing apogeotropic nystagmus: a...

We report a 44-year-old man who had apogeotropic nystagmus with the rotation of his head to either side from the supine position. His nystagmus lasted more than 2 minutes and was difficult to treat with. There were no neurological abnormalities except for the nystagmus and no findings suggesting intracranial disease on MRI. The head-position in which more intense nystagmus was evoked changed again and again in a short term. We diagnosed his illness as cupulolithiasis of horizontal canal, however, the affected ear could not be explained by any of the previously supposed mechanisms. In our case, we speculate the following mechanism. Otoliths were located on the right utricular side of the cupula. All of them were attached on the cupula at the beginning(attached phase) and then, some of them were detached from it(detached phase). The extent of the cupular deviation differed in each phase when the otoliths were beneath the cupula with his head turned to the left lateral position. According to Ewald's second law, more intense nystagmus is evoked when the cupula deviates toward the utricle than away from it. The patient's head-position in which more intense nystagmus was evoked changed according to the balance between the effect of Ewald's second law and the amount of otoliths detached from cupula. Our case showed that, in HC-BPPV with direction-changing apogeotropic nystagmus, we could not be certain about which ear was diseased. Therefore, it may be difficult to apply exercise therapy by determining the affected ear based on the head-position in which more intense nystagmus is evoked.