Diagnosis of Single- or Multiple-Canal Benign Paroxysmal Positional Vertigo according to the Type of Nystagmus
Figure 9
Pseudospontaneous nystagmus in horizontal canal BPPV. (a) When the head is erect, there is an angle of 30° between the horizontal plane and the horizontal semicircular canal, which may explain the pathogenesis of pseudospontaneous nystagmus. Any head movements would cause ampullofugal movement of otoconia, in case of canalolithiasis (geotropic type), provoking a nystagmus with fast phase towards the unaffected ear. In case of cupulolithiasis (apogeotropic type), the attached otoconial mass would cause deflection of the cupula in the opposite direction, triggering a reverse nystagmus. (b) When the head is bent 60° forward, pseudospontaneous nystagmus may change its direction, due to the inversion of the movement of otoconia (geotropic type) or of the deflection of the cupula (apogeotropic type). (c) When the head is bent backwards, pseudospontaneous nystagmus will increase, because the horizontal canal will approach the vertical position.
