Vertical acquired pendular nystagmus: oculomotor findings, localizing value and pathophysiology

OBJECTIVES: Evaluation of the localizing value and pathogenesis of vertical APN through examination of patients with this nystagmus form and different diagnosis. DESIGN: Three patients with vertical APN with different diseases (brainstem infarct, brainstem encephalitis and brainstem haemorrhage), but with similar topic of lesions, are presented. For registration of the nystagmus AC-electrooculography (EOG) was used. RESULTS: All patients were registered with spontaneous nystagmus with the following characteristics: vertical, conjugate APN with average frequency of 3.1 Hz and average amplitude of 7°. THE MAIN FINDINGS: Several main theories about the etiology and pathogenesis of the APN exist. According to the first one, this nystagmus form is due to the primary demyelination of the optical nerves, leading to a delay in visual feedback. However, the more popular theory is the one, according to which APN is due to certain abnormalities of the internal brainstem circuits, such as the connections between the brainstem nuclei and the cerebellum. CONCLUSIONS: Following the examinations, we were able to conclude that the lesions of the optical nerves are not the main reason, causing the APN, as all three patients did not have clinical and instrumental data for involvement of the visual pathways. From another point of view, all three patients had established brainstem lesions. The identical topic of the lesions suggested a connection between the vertical APN and this localization. The patients’ lesions were observed in the midbrain, mainly tegmental, paramedian, ventrolateral from the oculomotor nucleus, in the area of the red nucleus.