Incidence and Clinical Significance of Positional Downbeat Nystagmus in Posterior Canal Benign Paroxysmal Positional Vertigo.

Background and Purpose The aim of this study was to determine the incidence and clinical significance of positional downbeat nystagmus (pDBN) after treatment of posterior canal (PC) benign paroxysmal positional vertigo (BPPV). Methods We recruited 77 patients with a diagnosis of PC BPPV, and assessed the presence of pDBN during follow-up positional tests after performing the Epley maneuver. Results An immediate response to the Epley maneuver was exhibited by 57 of the 77 patients, with resolution of their positional torsional upbeat nystagmus (pT-UBN). Twenty-two (39%) of them exhibited pDBN during follow-up tests performed 1 hour later. The latency and duration of pDBN were 3.2 +/- 2.0 and 12.0 +/- 10.0 s (mean +/- SD), respectively. The maximum slow phase velocity of pDBN was 5.1 +/- 2.5 degrees, and ranged from 2.0 to 12.2 degrees. A torsional component was also observed in six patients. The patients with pDBN were much more likely to develop a typical form of PC BPPV again at a I-week follow-up (5/22, 23%) compared to those without pDBN (1/31, 3%; p=0.036). pDBN disappeared in all patients within 6 months. Conclusions Our study found transient pDBN in 40% of patients with PC BPPV after the immediate resolution of positional vertigo and pT-UBN. pDBN may be attributed to residual debris in the distal portion of the PC, which can move toward the ampulla producing an ampullopetal flow of endolymph during positioning.