This study describes patients with horizontal aperiodic alternating nystagmus (Â鶹´«Ã½Ó³»­)  in peripheral vestibulopathy and brainstem lesion and elucidates the possible mechanism of that.

We defined horizontal Â鶹´«Ã½Ó³»­ that it is repeat reversal of spontaneous horizontal nystagmus but markedly asymmetric and irregular unlike PAN(periodic alternating nystagmus). We consecutively recruited patients with horizontal Â鶹´«Ã½Ó³»­ from 5 different dizziness clinics of tertiary hospital from January 2018 to Jury 2019. Eye movements of all patients were recorded using video-oculography for a minimum 2 cycles. All patients had vestibular function test(caloric test, bedside or video head impulse test) and magnetic resonance imaging(MRIs). To determine the most relevant mechanism of horizontal Â鶹´«Ã½Ó³»­, we analyzed the pattern of nystagmus and classified with vestibular dysfunction and reasonable causes.

In rare cases, horizontal Â鶹´«Ã½Ó³»­ can occur due to various peripheral vestibulopathy from acute to chronic phase. the shortened time constant(impaired velocity storage mechanism) due to peripheral vestibulopathy can destabilize the adaptive process and cause a horizontal Â鶹´«Ã½Ó³»­.