Positional Nystagmus of Benign Paroxysmal Type (BPPN) Due to Cerebellar Vermis Lesions: Pseudo-BPPN

Positioning nystagmus accompanied by severe vertigo has been reported in patients with partial lesions of the inner ear, especially otolith lesions. Typically, this type of nystagmus shows a latent period and subsequent fatiguability. We concur with this finding and have constantly emphasized the significance of this phenomenon in clinical diagnosis. Since we started using CT-scanning, this type of nystagmus has been noted in 47 patients, all of whom had cerebellar vermis lesions. Attention should be focused on this association; if such a combination were seen in only 1 or 2 patients, it could simply be attributed to coincidence. But its occurrence in as many as 47 patients indicates a causal role of cerebellar vermis lesions. Its mechanism may be explained by incomplete inhibition of the vestibulo-oculomotor system including the cerebellar flocculonodular lobe or vestibulo-cerebellum.