Apogeotropic direction-changing positional nystagmus is considered to appear in patients with disorders of the central nervous system. However, this peculiar nystagmus is more likely to be caused by peripheral vestibular disorder. The mechanism of apogeotropic direction-changing positional nystagmus can be explained by benign paroxysmal positional vertigo (BPPV) caused by cupulolithiasis in the horizontal semicircular canal.
We used the canalith repositioning procedure (CRP) in a patiant with apogeotropic direction-changing positional nystagmus diagnosed as BPPV, and observed the change from upper-beating nystagmus to down-beating nystagmus during the procedure. The change in the direction of nystagmus seemed to indicate the dispersion of otolithic debris from the cupula, that is to say, the conversion of cupulolithiasis to canalolithiasis. We observed the disappearance of nystagmus and vertigo after three days.