Can Cupulolithiasis Affect the Time Constant or Gain of the Velocity Step Test?

Kim, Min Tae; Choi, Ji Eun; Lee, Min Young; Jung, Jae Yun

Abstract

OBJECTIVES
The nystagmus evoked by an angular velocity step is influenced by the cupula dynamics and the status of velocity storage mechanisms. This study questioned whether the cupulolithiasis of horizontal canal benign paroxysmal positional vertigo (HC-BPPV) affects the time constant or gain of the velocity step test.
METHODS
We performed a retrospective study of 30 patients who diagnosed with HC-BPPV and performed rotary chair test at Dankook University Hospital from June 2010 to May 2017. All patients had normal vestibular function on the sinusoidal harmonic acceleration test. According to the direction of nystagmus on the head roll test, we further divided the patients into "geotrophic" (canalolithiasis) and "apogeotrophic" (cupulolithiasis) groups. We compared the time constant (Tc), gain, and directional preponderance (DP) between the 2 groups. We also compared the time constant and gain between lesion side of BPPV and normal side in each group.
RESULTS
In the supine head roll, geotrophic nystagmus observed in 14 patients and apogeotrophic nystagmus observed in 16 patients. When parameters of the velocity step test compared according to lesion side of BPPV (per-rotary of lesion side, postrotary of lesion side, per-rotary of normal side, and postrotary of normal side), there were no significant differences in Tc, gain, and DP between the 2 groups. There were also no significant differences in Tc and gain between lesion side and normal side in each group.
CONCLUSIONS
We assumed that cupulolithiasis of HC-BPPV could affect the cupular deflection evoked by an angular velocity step, but there were no significant differences in Tc and gain between patients with cupulolithiasis and canalolithiasis.