Posterior semicircular canal benign paroxysmal positional vertigo presenting with torsional downbeating nystagmus: an apogeotropic variant

Abstract

The aim of this study is to verify the hypothesis that free-floating particles could sometimes localize into the distal portion of the non ampullary arm of the posterior semicircular canal (PSC) so that assuming the Dix-Hallpike's positions, the clot could move towards the ampulla eliciting a inhibitory torsional-down beating paroxysmal positional nystagmus (PPNy), instead of typical excitatory torsional-up beating PPNy. Among 45 patients with vestibular signs suggesting anterior semicircular canal paroxysmal positional vertigo (PPV), collected from February 2003 to August 2006, we detected a group of 6 subjects whose clinical findings showed a singular behaviour during follow-up. At the first check-up, all patients were submitted to different types of physical manoeuvres for ASC canalolithiasis. Patients were controlled during the same session and after one week. When we found that nystagmus was qualitatively changed we adopted the appropriate physical therapies for that sign. At a next check-up, after having performed some physical therapies, all patients had a typical PSC PPNy of the opposite side, with respect to that of the ASC initially diagnosed. Basing on these observations we conclude that PSC PPV, similarly to lateral semicircular canal PPV, could manifests in a apogeotropic variant.

Figure 1

Paroxysmal positional nystagmus due to unilateral right posterior semicircular canal (PC) lithiasis (excitatory stimulus). (a): Black arrows indicate the direction of nystagmus slow phase in the two eyes; white arrows indicate the direction of nystagmus fast phase in the two eyes. (b): Arrows indicate the ocular muscles involved in nystagmus generation. (c): The two labyrinths; arrow indicates the endolymphatic flow within the interested canal. On the left side of the figure: the right eye and the right labyrinth; on the right side of the figure: the left eye and the left labyrinth. A: anterior semicircular canal; L: lateral semicircular canal; P: posterior semicircular canal.

Figure 2

Paroxysmal positional nystagmus due to unilateral right anterior semicircular canal (AC) lithiasis (excitatory stimulus). (a): Black arrows indicate the direction of nystagmus slow phase in the two eyes; white arrows indicate the direction of nystagmus fast phase in the two eyes. (b): Arrows indicate the ocular muscles involved in nystagmus generation. (c): The two labyrinths; arrow indicate the endolymphatic flow within the interested canal. On the left side of the figure: the right eye and the right labyrinth; on the right side of the figure: the left eye and the left labyrinth. A: anterior semicircular canal; L: lateral semicircular canal; P: posterior semicircular canal.

Figure 3

Paroxysmal positional nystagmus due to unilateral left posterior semicircular canal (PC) lithiasis (inhibitory stimulus). (a): Black arrows indicate the direction of nystagmus slow phase in the two eyes; white arrows indicate the direction of nystagmus fast phase in the two eyes. (b): Arrows indicate the ocular muscles involved in nystagmus generation. (c): The two labyrinths; arrow indicates the endolymphatic flow within the interested canal. On the left side of the figure: the right eye and the right labyrinth; on the right side of the figure: the left eye and the left labyrinth. A: anterior semicircular canal; L: lateral semicircular canal; P: posterior semicircular canal.

Figure 4

Left PC PPV due to nonampullary arm canal lithiasis. If the clot is localized into the non ampullary arm of the PC, when the patient is brought into the head hanging positions, the otoconial mass moves towards the ampulla; this movement produces a ampullopetal endolymphatic current and generates an inhibitory discharge of the posterior ampullary nerve. Thick arrow: movement of PC movement during positioning; thin arrow: direction of endolymphatic current after positioning; dashed lines: positions gained by the clot and the cupula, after positioning.

Figure 5

Left PC PPV due to nonampullary arm canalolithiasis. Nystagmus does not reverse its direction when the patient returns into the sitting position: the lack of reversal could be due to the reduced movement of the clot in a restricted tract of the PC that, is in a roughly horizontal plane. Solid line: horizontal plane; dashed line: plane corresponding to that of nonampullary arm of PC in the sitting position.