[Clinical and pathogenetic aspects of positional nystagmus]

Positional nystagmus (PN) is a heterogeneous clinical phenomenon. Most often it develops in benign positional paroxysmal vertigo as a result of otolithiasis. Rarely PN is observed in cases of lesion location in the cerebellum and brainstem. Recently a theory of light cupula was suggested to explain persisting geotropic PN. It explains the development of nystagmus by the changes in the ratio of the density of cupula to the density of endolymph, making the former sensitive to gravitational forces. Several theories were suggested: lighter cupula theory, heavier endolymph theory, theories of light debris and of density difference between perilymph and endolymph. However, the exact mechanism of light cupula syndrome is unclear. Clear diagnosis of the causes of PN requires detailed evaluation of neurological status with the use of diagnostic tests and additional research methods.