Posterior Semicircular Canal Type Benign Paroxysmal Positioning Vertigo with Ageotropic Paroxysmal Positioning Nystagmus

Abstract

We report on 3 patients with typical benign paroxysmal positioning vertigo (BPPV) and atypical, paroxysmal positioning nystagmus. When the Dix-Hallpike test was performed, the patients exhibited an ageotropic nystagmus, different from that classically described in posterior semicircular canal BPPV. It was torsional-vertical with the vertical component beating downwards, and the torsional component was beating away from the lowermost ear. In both left and right Dix-Hallpike positions, the upper poles of the eyes were turning away from the lowermost ear. The atypical ageotropic paroxysmal positional nystagmus of the posterior semicircular canal was observed in the evolution of the BPPV in 2 patients and on the first examination in the third. Two patients had changing patterns of paroxysmal positioning nystagmus.

Feasibility of Using the Video-Head Impulse Test to Detect the Involved Canal in Benign Paroxysmal Positional Vertigo Presenting With Positional Downbeat Nystagmus

“…In fact, it is rarely evoked only by ipsilateral positioning and it usually exhibits longer time constant compared to typical BPPV-like nystagmus, lacking of both crescendo-decrescendo course and torsional components (3, 9-15). Moreover, it has been recently hypothesized that the same pDBN could also be generated by particles gravitating through the distal portion of the non-ampullary tract of PSC, close to the common crus [ (16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27); Figures 14A-D]. In this condition, provoking maneuvers should move debris toward PSC-ampulla leading to an inhibitory discharge of PSC-afferents, which in turn results in pDBN with torsional components beating toward the contralateral ear ( Figure 14C).…”

“…Despite detached otoconia, moving inside unusual sites of the labyrinth, represent the assumed underlying mechanism, peripheral pDBN patterns show features classically known as central such as lack of torsional components and long time constant (9,11,15). More recently, it has been hypothesized that even otoliths settling in the distal portion of the non-ampullary tract of the posterior semicircular canal (PSC) may result in pDBN (16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). This type of PSC-BPPV has been named "apogeotropic variant" (18,20) as nystagmus evoked in provoking positions beats away from the ground and in the opposite direction to positional paroxysmal upbeat nystagmus (beating toward the ground in DH positioning, therefore geotropic) due to classical BPPV involving PSC ampullary arm.…”