Galvanic Vestibular-Evoked Myogenic Potentials in Unilateral Vestibular Schwannoma: Paired-Ear Differences and Contralateral Abnormalities

Background/Objectives: To characterize paired-ear vestibular-evoked myogenic potential (VEMP) response patterns and contralateral abnormalities in patients with MRI-confirmed unilateral vestibular schwannoma (VS). Methods: This exploratory retrospective paired-ear study included 24 patients with unilateral VS confirmed by contrast-enhanced MRI. Patients underwent pretreatment pure-tone audiometry, caloric testing, air-conducted sound cervical VEMP (ACS-cVEMP), bone-conducted vibration ocular VEMP (BCV-oVEMP), galvanic vestibular stimulation cervical VEMP (GVS-cVEMP), and GVS-oVEMP. Tumor-affected and contralateral non-tumor ears were compared using McNemar’s and Wilcoxon signed-rank tests. Age was compared by contralateral VEMP status using Mann–Whitney U tests. All p values were unadjusted for multiple comparisons. Results: Hearing loss and caloric abnormalities were more frequent in tumor-affected ears (91.7% vs. 20.8% and 62.5% vs. 8.3%, respectively; both p < 0.001). Abnormality rates were higher in tumor-affected than contralateral non-tumor ears for ACS-cVEMP (83.3% vs. 45.8%; p = 0.022), GVS-cVEMP (70.8% vs. 20.8%; p = 0.002), and GVS-oVEMP (70.8% vs. 16.7%; p = 0.002), whereas the BCV-oVEMP difference was not significant (62.5% vs. 33.3%; p = 0.092). Tumor-affected ears showed prolonged GVS-cVEMP p13 latency (median, 12.47 vs. 11.35 ms; p = 0.008) and reduced amplitude (median, 59.02 vs. 66.24 μV; p = 0.044). Patients with contralateral ACS-cVEMP abnormalities were older than those with normal responses (median, 62 vs. 45 years; p = 0.001); age did not differ significantly by contralateral GVS-VEMP status. Conclusions: In this exploratory paired-ear study, GVS-cVEMP abnormalities were more frequent in tumor-affected ears, and the observed contralateral abnormality rate was numerically lower than that for ACS-cVEMP. GVS-cVEMP may complement conventional VEMPs when contralateral abnormalities complicate interpretation. These preliminary findings require validation in larger prospective controlled studies.