Horizontal canal benign paroxysmal positioning vertigo

Abstract

Bithermal caloric stimulation in a patient with a benign paroxysmal positioning vertigo of the horizontal (lateral) semicircular canal (HC-BPPV) revealed a significant hypoexcitability of the affected ear that was reversible when treated by liberatory maneuvers. Both the positional vertigo and caloric hypoexcitability in HC-BPPV are caused by canalolithiasis, a concept strongly supported by the intensity of the positioning nystagmus being maximal when the patient turned his head around the longitudinal z-axis from the left lateral to right lateral position while recumbent (maximum slow-phase velocity [SPV] 176 deg/sec) and being much lower (maximum SPV 55 deg/sec) when he turned his head to the right lateral position while in a supine position (nose up). The dependence of this difference in nystagmus intensity on the initial head position and direction of rotation indirectly proves that the clot moves freely (to and fro) within the segment of the HC diametrically opposite to the ampulla. The reversibility of ipsilateral caloric hypoexcitability is attributed to the clot's (functional) plugging of the HC, which agrees with studies in squirrel monkeys. These data support the view that physiologic caloric responses consist of a major convective and minor nonconvective component.

Spontaneous Plugging of the Horizontal Semicircular Canal With Reversible Canal Dysfunction and Recovery of Vestibular Evoked Myogenic Potentials

“…Of particular interest was a remarkable eye velocity trajectory that saturated at approximately 80-/s as if the cupula was kept at a constant deflection, regardless if head velocity increases up to 300-/s. Reversible low-frequency VOR hypofunction has been previously reported in hBPPV canalolithiasis using calorics (9).…”

Nystagmus during neck flexion in the pitch plane in benign paroxysmal positional vertigo involving the horizontal canal

“…An asymmetrical response of the induced nystagmus has been explained by Ewald's second law which states that irritative stimuli are more effective than inhibitory ones in inducing vestibular responses [17]. However, the intensity of the direction-changing positional nystagmus in HC-BPPV may be affected by several factors, such as initial location of the otolithic debris in the canal, and the net angle and acceleration of head rotation, making it difficult to lateralize the involved ear by comparing intensities of induced nystagmus in some patients [14].…”

“…A diagnosis of HC-BPPV was based on the following features: (1) a history of brief episodes of vertigo provoked by head motion [14], (2) direction changing horizontal nystagmus during the head-rolling tests, which may beat toward the lowermost (geotropic) or uppermost ear (apogeotropic), and (3) no other identifiable disorders of the central nervous system. The geotropic nystagmus usually developed with a short latency of several seconds [8], whereas the apogeotropic nystagmus mostly showed a maximum intensity immediately after positioning and usually persisted [11,12,15].…”

Benign paroxysmal positional vertigo: Diagnostic criteria

“…Caloric irrigation of the affected ear [70] and the head thrust test [35] may reveal horizontal canal paresis (possibly due to partial plugging of the canal) that is reversible after successful positional therapy [70].…”