Atypical to Typical Posterior Semicircular Canal Benign Paroxysmal Positional Vertigo (BPPV): Bascule Maneuver in Short-Arm Posterior Canal BPPV

INTRODUCTION

Benign Paroxysmal Positional Vertigo (BPPV) is the most common peripheral vestibular disorder, typically due to canalolithiasis in the periampullary region of the long arm of the posterior semicircular canal (PSC). While the classical variant involves the periampullary region of the long arm of the posterior semicircular canal, atypical presentations, including the short arm variant, have been described, often posing diagnostic and therapeutic challenges. We present a case where the Bascule maneuver facilitated the transformation of short-arm PSC canalolithiasis to a treatable periampullary variant.

CASE REPORT

A 51-year-old female presented to our otoneurology services in October 2024 with 2 days of positional vertigo and non-positional disequilibrium. Neurological examination was unremarkable. The left Dix-Hallpike test (DHT)¹ elicited persistent left torsional upbeating nystagmus lasting over 60 seconds. The nystagmus ceased in the right lateral recumbent (with a nose down) position (negative inversion test) and reappeared upon returning to the left DHT. Sitting up from the left DHT also triggered upbeating left torsional nystagmus. Based on the findings of the oculomotor responses during positional tests, a diagnosis of left short arm PSC canalolithiasis was made.² The patient underwent treatment with the Bascule maneuver. Performing the Bascule maneuver [Figure 1] required a precise sequence of steps. The procedure began with a 45-degree rotation of the patient’s head toward the unaffected right side, followed by a prompt transition into the lateral recumbent nose-down position, similar to a demi-Semont maneuver.³ Next, the patient’s head and torso were swiftly rotated 180 degrees onto her affected left side, positioning her nose up. This was followed by a rapid 180-degree reversal to the uninvolved side, resulting in a nose-down position on the right. A total of five such sequences were performed on each side (right and left).

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Figure 1

Bascule Maneuver: Illustrated steps show otoconia translocation from the short arm to the long arm of the posterior semicircular canal (PSC) across three positions with corresponding canal orientation: A (short arm to common crus via utricle), B (common crus to the lowest point of the long arm), and C (lowest point of the long arm to the periampullary region). (Conceptualized by the corresponding author; illustrated by Ashraf Hussain using CorelDraw Suite 2019).

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On follow-up after 24 hours, the left DHT elicited typical crescendo-decrescendo left torsional upbeating nystagmus lasting about 20 seconds, consistent with periampullary PSC canalolithiasis. Subsequently, five sessions of the Epley maneuver were conducted. After another 24 hours, the patient was asymptomatic, with no nystagmus in positional testing. Video documentation of the transformation from short arm to typical (periampullary) long arm left posterior semicircular is available online [Supplementary video 1].

DISCUSSION

PSC-BPPV commonly results from otoconia dislodgement into the periampullary location of the long arm, eliciting transient vertigo and nystagmus during DHT. However, rare variants like short-arm canalolithiasis or cupulolithiasis can mimic typical forms yet exhibit resistance to maneuvers like Epley. The short arm of the PSC connects the ampulla to the utricle and can harbor debris that fails to move with conventional repositioning techniques.⁴ Büki et al.⁵ described Type 2 BPPV as a result of chronic low-grade canalolithiasis in the short arm of the posterior semicircular canal.⁵ Taura et al.⁶ similarly reported persistent nystagmus unresponsive to the Epley maneuver but responsive to vibration therapy.⁶ Kim et al.⁷ innovated an augmented half Dix-Hallpike maneuver that could unmask positional nystagmus in suspected short-arm posterior semicircular canalolithiasis.⁷ In this patient, the Bascule maneuver was successful in translocating otoconia to the periampullary segment, allowing subsequent resolution with the Epley maneuver.⁸ This sequence supports prior findings from Ping et al.,⁹ who possibly observed similar therapeutic transformation with the Bow and Yaw Maneuver.⁹ Alternate explanations include cupulolithiasis, particularly if debris adheres to the cupula’s short-arm surface.¹⁰ The negative inversion test and elicitation of nystagmus when sitting up are supportive of a non-long-arm pathology. Scocco et al.² emphasized that cupula orientation and gravity vector interactions are central to generating nystagmus patterns.²

CONCLUSION

Recognition of atypical PSC-BPPV variants is crucial for effective management. The Bascule maneuver offers a promising approach to convert short-arm canalolithiasis into a treatable form. Incorporation of this maneuver should be considered in patients unresponsive to standard repositioning techniques.