RESUMO
Detection of nystagmus is an important diagnostic clue in patients with acute vertigo. Patients with peripheral disorders exhibit nystagmus with a constant direction whereas those with central disorders exhibit nystagmus with changes in direction with or without gaze fixation. Periodic alternating nystagmus (PAN) is a horizontal or horizontal-rotary jerk-type nystagmus that reverses its direction with time. PAN is typically observed in patients with central disorders, such as cerebellar or pontomedullary lesions, but it is also observed in patients with peripheral disorders, albeit rarely. Here we report a rare case of a 58-year-old patient with vertigo with PAN, which was initially suspected as a central disorder, but eventually diagnosed as a peripheral vestibular disorder. We investigated the characteristics and mechanisms of peripheral PAN in this case. The absence of central disorder symptoms, visual suppression of PAN, normal oculomotor findings, and transient persistence are important diagnostic clues for differentiating peripheral from central PAN.