Is galvanic VEMP a prediction of the nerve origin and damage in patients of vestibular schwannoma

Background: Recent studies proved that certain proportions of vestibular schwannoma (VS) originated other than vestibular nerve of the eighth cranial nerve. Aims/objectives: Unlike air-conducted sounds (ACS) and bone-conducted vibration (BCV), galvanic vestibular stimulation (GVS) evokes vestibular evoked myogenic potentials (VEMPs) from the vestibular nerve. Materials and methods: Case-control study was conducted in unilateral VS patients pre-operatively. Healthy ears were controls. Patients examined ACS, BCV and GVS ocular VEMP (oVEMP) and cervical VEMP (cVEMP), caloric test, video head impulse test (vHIT), suppression head impulse paradigm (SHIMP) and pure tone audiometry (PTA). Results: Seven (26.9%) tumors affected left ear and 19 (73.1%) on the right(p < .05). Response rates in VS group were statistically lower than control except for ACS-cVEMP (p < .05). Response rates of VEMPs in VS patients decreased with the tumor size grows. But not all BCV and GVS VEMPs disappeared in the largest tumor group. Abnormal rates of caloric test, vHIT gains and SHIMP were found. Conclusions and significance: Response rates of GVS VEMPs decreased with the residual functional nerve fibers. GVS VEMPs help to differentiating labyrinthine and retro-labyrinthine lesions. GVS combined with BCV VEMPs probably reflex the tumor origin from the eighth cranial nerve and/or the remaining vestibular function.