Transitory, counterolling and pure-rotatory positioning nystagmus caused by cerebellar vermis lesion.

Positioning nystagmus with a latent period, accompanied by severe vertigo along with nystagmus, with subsequent fatiguability has been reported in patients with partial lesions of the inner ear, especially otolith lesions. We agree with this opinion 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, but its occurrence in as many as 20 patients suggests a causal role of cerebellar vermis lesions. The explanation may be incomplete inhibition of the vestibulo-oculomotor system by the cerebellar flocculo-nodular lobe or vestibulocerebellum.