Lindsay-Hemenway Syndrome Involving the Horizontal Semicircular Canal: Some Considerations Upon Residual Canal Afferents in BPPV Secondary to an Ipsilateral Acute Unilateral Vestibulopathy.

OBJECTIVE

To describe benign paroxysmal positional vertigo (BPPV) involving the horizontal semicircular canal (HSC) after ipsilateral acute unilateral vestibulopathy (AUVP) and to advance some hypotheses on the underlying pathomechanism.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

A case series of four patients presenting with HSC-BPPV after ipsilateral AUVP with impaired function of the involved canal at the video-head impulse test (vHIT). Ipsilateral sudden sensorineural hearing loss was detected in one case.

INTERVENTION

All patients underwent bedside examination and an instrumental audio-vestibular assessment, including pure-tone audiometry, vHIT, and vestibular-evoked myogenic potentials. Three patients underwent bithermal caloric testing (BCT). Brain magnetic resonance imaging scan was performed in all cases. Successful canal repositioning was conducted.

MAIN OUTCOME MEASURE

Clinical presentation with video recording and audio-vestibular findings.

RESULTS

Secondary HSC-BPPV was observed from 3 weeks to 8 months after the onset of ipsilateral AUVP. Two cases exhibited an apogeotropic variant, whereas two cases presented with a geotropic form. All BPPV resolved after physical therapy. Instrumental audio-vestibular assessment revealed vestibulo-ocular reflex (VOR) impairment for the affected canal on vHIT in all cases, whereas BCT revealed a borderline normal canal paresis.

CONCLUSIONS

BPPV after an AUVP can involve the HSC. A reduced VOR gain in the high-frequency domain attributable to a damage of the type I (phasic) afferents does not exclude the occurrence of a BPPV if type II (tonic) afferents are preserved or slightly impaired. Clinicians should not neglect to evaluate for provoking nystagmus in patients with vestibular symptoms and vestibular hypofunction on vHIT.