ABSTRACT
Bowing nystagmus, lying down nystagmus, null pointand comparing the slow phase velocity during right and left head roll test may be used to distinguish the side of lesion in lateral canal benign paroxysmal positional vertigo (BPPV). Nonetheless, it is sometimes difficult to distinguish the side of lesion. In particular, when multiple canal BPPV such as lateral and posterior canal BPPV is suspected, the problemis even more complicated. From this reason, usually the side of lesion is first identified for the posterior canal, and the lateral canal BPPV is presumed to be present on the identical side. But is this approachalways correct and justifiable? As there are reports on bilateral posterior canal BPPV and bilateral lateral canal BPPV, there should also be bilateral posterior and lateral canal BPPV cases. We report two cases of bilateral posterior and lateralcanal BPPV, and discuss the grounds for diagnosing these cases as bilateral. The first case is a mixed left posterior canalolithiasis plus right lateral canalolithiasis and the second case is a mixed right posterior canalolithiasis plus left lateral cupulolitiasis. In such cases, mixed nystagmus can make it difficult to directly compare the slow phase velocity during the right and left head roll test. New methods are necessary to distinguish the side of the lesion for the lateral canal. We introduce the concept of AHC (attenuated horizontal component) which seems to be important in deciding the side of lesion in multiple canal BPPV. We also introduce head center nystagmus (HCN) to aid the decision on the side of lesion.