Unilateral benign paroxysmal positioning vertigo (BPPV) may mimic bilateral BPPV if the diagnostic positioning maneuver is executed without appropriate alignment of the head and neck with the trunk.
Appropriate alignment is achieved by adjusting the plane of the affected posterior semicircular canal so that it is parallel to the plane of diagnostic head tilt, ie, 45° horizontal head rotation to the left before a head tilt to the right in suspected right-sided BPPV. With inappropriate head alignment and head tilt to the side of the unaffected ear, a free-floating clot within the long arm of the uppermost posterior canal may gravitate toward the cupula and become settled on it. This causes ampullopetal cupulolithiasis, evoking geotropic nystagmus, which may mimic BPPV of the unaffected ear.
This hypothesis explains the seemingly paradoxical observation of immediate relief from "bilateral BPPV" following unilateral surgical canal occlusion on the "more symptomatic" side.(Arch Otolaryngol Head Neck Surg. 1994;120:1339-1341)
Steddin S, Brandt T. Unilateral Mimicking Bilateral Benign Paroxysmal Positioning Vertigo. Arch Otolaryngol Head Neck Surg. 1994;120(12):1339–1341. doi:10.1001/archotol.1994.01880360037007
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