Integrity of Brainstem Connections in Essential Tremor Using Auditory and Vestibular Evoked Potentials

Essential tremor (ET) is associated with various of non-motor symptoms including hearing impairment and imbalance attributed to the neurodegenerative ET pathology affecting brainstem structures.

This study aimed to assess auditory and vestibular brainstem functions in patients with ET in comparison to controls using auditory brainstem responses (ABR) and cervical and ocular vestibular-evoked myogenic potentials (cVEMP and oVEMP), and to correlate their dysfunction to disease characteristics.

24 patients (48 ears) with ET and 24 healthy controls were recruited and assessed by ABR, cVEMP and oVEMP. Patients were assessed by Fahn-Tolosa-Marin Tremor Rating Scale (FTM-TRS) and functional gait assessment scale.

High-rate ABR showed significant increase of waves III and V latencies and I-V interpeak latencies among patients, compared to age and gender matched controls. Low-rate ABR showed less significant differences; right, I-III and I-V interpeak latencies, and average I-III interlatences. ET patients showed prolonged latencies of P1 and N1 waves of cVEMP (P = 0.007 and P = 0.003), average P1-N1 latency and amplitude differences (P < 0.001) and P1 latency of oVEMP (P = 0.009), compared to controls, with more differences in cVEMP than in oVEMP. Age, age of onset, disease duration showed correlations with ABR responses, tremor severity correlated with oVEMP, while functional gait scores correlated with both.

The study confirmed and localized the dysfunction of the auditory and vestibular brainstem connections in ET and demonstrated a possible correlation with tremor severity and associated gait dysfunction.