Benign paroxysmal positional vertigo--toward new definitions

OBJECTIVE: To review new clinical data and theories concerning atypical positional nystagmus in vertical canal benign paroxysmal positional vertigo (BPPV).

DATA SOURCES: Peer reviewed, clinical papers describing nystagmus provoked by positioning in cases with BPPV.

STUDY SELECTION: Basic scientific articles detailing 3D anatomical reconstructions of the inner ear.

CONCLUSION: In BPPV, it is hypothetically possible that otoconia become dislocated but do not fall into the common crus of the vertical canals or into the horizontal canal; in these cases, they may gravitate toward the most inferior part of the utriculus, the ampulla of the inferior canal. It is argued that in these cases, depending on their behavior (free-floating or sticking to the cupula) and the precise position of the inferior ampulla, either no nystagmus or a slow downbeat nystagmus should ensue when the patient is positioned from sitting to a Dix-Hallpike position. Such scenarios could hypothetically explain commonly seen clinical entities such as "subjective BPPV" and/or cases with a peripheral positional downbeat nystagmus.