Abstract
This is a case report of oblique periodic alternating nystagmus (PAN). This unusual nystagmus is provoked by intermittent vertebral artery compression (Powers' syndrome). Periodic alternating nystagmus (PAN) is rarely associated with oblique nystagmus. The nystagmus observed in this case seemed to consist of two superimposed types of nystgmus: horizontal PAN and downbeat nystag-mus. The mechanism of PAN is not known. However, lesions in the vestibulocerebellum or neighboring sites in the brainstem are known to have caused some cases of PAN. Downbeat nystagmus has also been produced by a lesion in the vestibulo-cerebellum. It was impossible to distinguish lesions in the vestibulocerebellum from those in the brainstem in this case. Nonetheless, the evidence, taken together, indicates that the cause of oblique PAN in this case could be lesions in the uvula and nodulus or in the related neural network in the brainstem.
