Positional nystagmus.

Positional nystagmus (PN) appears in certain positions of the head. The peripheral type of PN is a paroxysmal nystagmus which appears after a latent period and which has both adaptation and fatigability. Positional vertigo of the peripheral type can sometimes be related to middle ear affections or head trauma, causing detachment of otoconia in the vestibular apparatus. The condition can also be correlated to disturbed blood circulation, ageing, vascular loops and Borreliosis. PN of the central type is direction changing and does not have a latent period or adaptation and fatigability. Etiological factors are drugs, posterior fossa tumours, vascular disturbance and multiple sclerosis.