Prolonged Positional Downbeat Nystagmus in Benign Paroxysmal Positional Vertigo: A Case Report and Literature Review.

Purpose This study aimed to report an unusual case of benign paroxysmal positional vertigo (BPPV), who showed prolonged positional downbeat nystagmus without latency and was diagnosed with cupulolithiasis of the anterior canal (AC). We compared this case with one of typical AC-BPPV, and possible mechanisms underlying the atypical characteristics were discussed. Method Two patients diagnosed with AC-BPPV were reported. Positional testing using video-oculography goggles was performed, and outcomes were measured via medical records and analysis of videos of the nystagmus. Results Downbeat nystagmus was observed in the contralateral Dix-Hallpike test in both cases. The torsional component was subtle or absent, but motion was induced toward the affected ear. The two cases differed in latency and duration of vertigo, as well as habituation. The patient with atypical nystagmus showed little or no latency and longer duration. Moreover, there was no habituation on repeated tests. The nystagmus showed several differences from that of typical AC-BPPV. Conclusions Based on our case, AC-BPPV may induce various unusual clinical manifestations of nystagmus. Accurate diagnosis requires careful consideration of the patient's symptoms and the characteristics of the nystagmus. Supplemental Material https://doi.org/10.23641/asha.14265356.