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Benign positional nystagmus

A study of its three-dimensional spatio-temporal characteristics

From the Neurology Department, Royal Prince Alfred Hospital, Sydney, Australia.

Address correspondence and reprint requests to Dr. Swee T. Aw, Neurology Department, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Sydney, Australia; e-mail: sweea{at}icn.usyd.edu.au

Objective: To describe the spatial and temporal characteristics of benign positional nystagmus (BPN) subtypes in benign positional vertigo (BPV) due to vestibular lithiasis affecting one or more semicircular canals (SCCs).

Background: Activation of SCC receptors by sequestered otoconia, either freely moving (canalithiasis) or cupula-adherent (cupulolithiasis) during head position changes with respect to gravity, is the accepted cause of BPV. Although accurate identification and interpretation of BPN is critical to BPV therapy, no rigorous, kinematically correct three-dimensional spatio-temporal analysis of BPN in all its forms exists.

Methods: Using dual-search scleral coils, the authors recorded BPN provoked by Dix–Hallpike or supine ear-down test in a two-axis whole-body rotator in 44 patients with refractory BPV. To localize the SCC affected, BPN rotation axes were compared to SCC axes, axes orthogonal to average SCC planes.

Results: Sixteen patients had upbeat, geotropic-torsional BPN in the Dix–Hallpike test to one side and five to both sides, with BPN rotation axes clustered around the lowermost posterior SCC axis. Seven had direction-changing horizontal BPN, three geotropic (canalithiasis) and four apogeotropic (cupulolithiasis), with rotation axes around the lowermost and uppermost horizontal SCC axis. Seven had predominantly downbeating BPN with rotation axes clustered around one superior SCC axis. Nine had upbeat, horizontal-torsional BPN with rotation axes located between posterior and horizontal SCC axes of the lowermost ear suggesting simultaneous lithiasis in both SCCs. BPN vector-guided repositioning therapy was successful in 43 patients.

Conclusion: Benign positional vertigo can affect one or more semicircular canals and three-dimensional recording with vector analysis of the benign positional nystagmus (BPN) can guide canalith repositioning therapy especially in refractory cases with atypical BPN.

Additional material related to this article can be found on the Neurology Web site. Go to www.neurology.org and scroll down the Table of Contents for the June 14 issue to find the title link for this article.

Supported by National Health and Medical Research Council (Project Grant 293801), the Brain Foundation, and the Neurology Trustees, Royal Prince Alfred Hospital.

Received April 7, 2004. Accepted in final form February 16, 2005.

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