RESUMO
In some dizzy patients the apogeotropic direction changing positional nystagmus (DCPN) can be caused by a central disorder such as a mass lesion near the fourth ventricle or infaction. We have recently encountered a patient who showed a central DCPN mimicing a horizontal canal cupulolithiasis benign paroxysmal positional vertigo (BPPV). A 4.1 cm sized tumor was filling the fourth ventricle before the operation. When the head was turned to the left side vigorous right beting nystagmus was found. When the head was turned to the right side vigorous left beting nystagmus was found. But unlinke the typical horizontal canal BPPV, bowing and lying down position did not elicit any nystagmus. In order to see if the central DCPN was a transient finding or a persistent finding, we checked the nystagmus 3 weeks after the first testing. The same pattern of nystagmus was found again. The video head impulse test gain of all six canals were within the normal limit. In this article we discuss the points how to suspect a central DCPN in such cases.