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.