Skull vibration induced nystagmus frequency and location optimization in severe unilateral lesion patients and in anterior canal dehiscences

Abstract

Background Bone conducted vibrations (BCV) applied on mastoid elicit in common unilateral vestibular lesion (UVL) patients usually a skull vibration induced nystagmus (SVIN) beating toward the intact side and conversely in unilateral superior semicircular canal dehiscence (SCD) a SVIN beating toward the lesion side. Our purpose was to establish optimal topographic and frequency stimulations in severe UVL (SUVL) and SCD patients. The second aim was to compare VIN at 100 Hz in unilateral SCD (uSCD) and bilateral (bSCD) patients. Participants and methods The first experiment included 11 SUVL and 10 unilateral SCD (uSCD). The SVIN, optimal frequency was studied with a MiniShaker BK the VIN slow phase velocity (SPV) was recorded with Videonystagmography. Optimal topographic stimulation study analyzed vertex and mastoids responses SPV at 100 Hz. Second experiment included 27 uSCD and 13 bSCD and analyzed SVIN SPV at 100 Hz. Results In SUVL, the optimal stimulus frequency was 100 Hz for the horizontal component VIN SPV ( P P = 0.02) and at 600 Hz ( P = 0.01); conversely VIN SPV at 100 Hz was higher in SUVL than uSCD ( P = 0.008). In SUVL, mastoid stimulation was significantly more efficient than vertex stimulation (ANOVA P = 0.01). Conversely, in uSCD SVIN SPV was significantly higher after vertex stimulation ( P = 0.04). A VIN was significantly more often observed in uSCD than bSCD ( P = 0.009) and VIN SPV was higher in uSCD than bSCD ( P = 0.008). Conclusion In SUVL, the optimal frequency stimulation is 100 Hz with no responses over 500 Hz. In SCD, patients responses are observed up to 700 Hz without significant optimal frequency suggesting that the BC facilitation related to the existence of a third window enables a greater sensitivity to higher range of frequencies. Vertex stimulations are more efficient in SCD patients and higher responses are observed in uSCD than bSCD. SVIN acts as a vestibular Weber test.