A Possible Role of Video-Head Impulse Test in Detecting Canal Involvement in Benign Paroxysmal Positional Vertigo Presenting With Positional Downbeat Nystagmus.

To describe the possible diagnostic role of video-head impulse test (vHIT) in patients presenting with positional downbeat nystagmus (PDN) due to benign paroxysmal positional vertigo (BPPV) involving the anterior canal (AC) or the non-ampullary arm of the posterior canal (PC). Three patients presenting with positional vertigo, PDN, symmetrical cervical and ocular vestibular-evoked myogenic potentials, and selective deficit of the vestibulo-ocular reflex (VOR) gain for a single vertical canal on vHIT. Diagnostic evaluation and rehabilitative treatment for BPPV involving the deficient canals. Video-oculographic and vHIT findings before and after canalith repositioning procedures (CRP) for AC-BPPV and apogeotropic PC-BPPV. Each patient was treated with CRP for BPPV involving the hypoactive canal. In one case, symptoms receded with physical therapy, whereas two patients developed a paroxysmal positional upbeat nystagmus consistent with BPPV involving the ampullary arm of the ipsilateral PC and were treated with Epley CRP. Posttreatment evaluation showed resolution of symptoms and signs and restitution of canal function in all cases. PDN can be due to both peripheral and central vestibular pathologies. In case of BPPV, involvement of the non-ampullary arm of the PC is hardly distinguishable from contralateral AC canalolithiasis. In these situations, vHIT may play a key role in the differential diagnosis. Considering these findings, we propose to include vHIT in the test battery of patient with PDN, as it may provide clues to the differential diagnosis with central pathologies enabling the identification of the canal involved by BPPV.