No abstract

The most common form of posterior canal benign paroxysmal positional vertigo (BPPV) is characterised by positional, paroxysmal, upbeat nystagmus, with a torsional component beating towards the downward ear. Rarer variants have been reported, putatively due to either the position of otoconia in the canal or anatomic variations of the semicircular canals. The most frequent less common form is apogeotropic posterior canal BPPV, in which the positional nystagmus is downbeat and torsional apogeotropic. In this form, the main problems are differential diagnosis with central mimics of BPPV and identification of the affected canal and its side. The authors propose a new subtype of apogeotropic posterior canal BPPV hypothesising the localization of otoconia in the ampullary tract of the affected canal, which might explain the modality of the conversion in typical posterior canal BPPV which they observed in some of these cases. If nystagmus of the less common forms of posterior canal BPPV is explicable through purely peripheral mechanisms, these forms should no longer be defined as "atypical" but, in a less demanding way, as "less common" variants, which must be recognised by any expert otoneurologist.

A 60-second hyperventilation event causes metabolic changes in the vestibular system and reveals a latent vestibular asymmetry. The presence of an excitatory pattern is the major criterion that suggests VS in patients with signs of unilateral vestibular deficit.

SUMMARY Objective Study the high-frequency vestibulo-oculomotor reflex in posterior canal benign paroxysmal positional vertigo (BPPV) through Video Head Impulse Test (vHIT). Methods 150 patients suffering for the first time from posterior canal BPPV were studied. Posterior canal vestibulo ocular reflex (VOR) gain was analysed through stimulations in right anterior-left posterior and left anterior-right posterior planes before treatment, immediately after resolution of the acute stage and one month later. Results were compared with a group of 100 healthy individuals. Results No significant difference between the study the control groups was observed, except for normalised asymmetry ratio of the posterior canal which was significantly higher in the study group. VOR gains of both affected posterior canals and contralateral healthy posterior canals were not significantly correlated with the VOR gain of ipsilateral and contralateral anterior canals. Conclusions vHIT does not seem to represent an essential tool to study typical posterior canal BPPV in patients affected by this disease for the first time. Different results might be expected in relapsing forms, non-responsive forms, long lasting forms, or atypical variants in which major damage could be provoked by the persistence of otoconia in the canal or by its complete or partial jam.