Positional nystagmus of benign paroxysmal type (BPPN) due to cerebellar vermis lesions. Pseudo-BPPN.

Positioning nystagmus accompanied by severe vertigo had been reported in patients with partial lesions of the inner ear, especially otolith lesions. Typically this type of nystagmus represents 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 to use CT-scanning, this type of nystagmus has been noted in 20 patients, all of whom had cerebellar vermis lesions. Attention should be focused on this association. A simple coincidence could not be excluded if such a combination were seen in only 1 or 2 patients, it could be attributed to simple coincidence. But its occurrence in as many as 20 patients 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 vestiburo-cerebellum.