Masseter Vestibular Evoked Myogenic Potentials (M-VEMPs) in Vestibular Neuritis.

Introduction: Masseter vestibular evoked myogenic potentials (M-VEMPs) are a recent tool for assessing a vestibulo-trigeminal pathway departing from the saccule, similarly to cervical VEMPs (C-VEMPs), that evaluate saccular function via the sternocleidomastoid muscle. M-VEMPs may offer a complementary diagnostic value in vestibular neuritis (VN). Methods: This retrospective study analysed M-VEMPs and C-VEMPs in 28 monolateral patients and 1 bilateral (30 ears) diagnosed with VN between 2023 and 2024. Diagnostic evaluation included video head impulse tests (VHIT), caloric tests, ocular VEMPs, and, in a few cases, electromyography (EMG) of the sternocleidomastoid muscle. M-VEMPs were elicited using 500 Hz tone bursts at 97 dB nHL. Results were compared based on the topography of vestibular involvement and muscle response concordance. Results: M-VEMPs were always present in patients with superior VN and intact saccular function, showing consistent results with normal C-VEMPs. In some cases, with saccular dysfunction, M-VEMPs were preserved despite the absence of C-VEMPs, suggesting greater robustness. One patient with herpes zoster (HZ) involving both the VIII and trigeminal nerves showed absent M-VEMPs, indicating trigeminal pathway involvement. Edentulous patients showed reduced or absent M-VEMPs due to compromised masseter muscle electromyography activity. Conclusions: M-VEMPs are reliable and often concordant with C-VEMPs in VN but may reveal additional diagnostic information in discordant or complex cases. They are particularly useful in identifying trigeminal involvement but are limited in patients with poor masseter muscle function. Further studies are needed to clarify their full diagnostic potential.