Abnormal vestibular evoked myogenic potentials in medial medullary infarction

Abstract

Background: The medial vestibulospinal tract (MVST), which descends in the medial longitudinal fasciculus (MLF), may mediate the vestibular evoked myogenic potentials (VEMPs) in the contracting sternocleidomastoid muscle. We report herein abnormal VEMPs in a patient with medial medullary infarction (MMI) that appeared to involve the MLF.

Case report: A patient with infarction involving the right medial medulla showed decreased p13-n23 amplitude and increased p13/n23 latencies of the VEMPs on the right side. These abnormal VEMPs recorded in an MMI patient support the theory that VEMPs are mediated by the MVST contained within the MLF.

Conclusions: VEMPs may represent a valuable tool for investigating vestibular dysfunction originating from the saccule, even in patients with central vestibulopathies, which is not readily defined by conventional vestibular function tests.

Keywords: medial medullary infarction; saccule; vestibular-evoked myogenic potentials.

Fig. 1

Vestibular evoked myogenic potentials (VEMPs) recorded from the contracting ipsilateral sternocleidomastoid muscle exhibit decreased p13-n23 amplitude and increased p13/n23 latencies on the right side. The stimuli were short, alternating tone bursts (95 dB nHL, 108 dB SPL; 500 Hz; ramp=2 ms; plateau=3 ms) presented at 2.1 Hz monaurally. To compare the normalized p13-n23 amplitude of VEMP responses on the affected side with those on the intact side, the interaural difference ratio (IAD) of the normalized amplitude (IAD_amp, %) was calculated using [(Au-Aa)/(Aa+Au)×100], where Au is the normalized p13-n23 amplitude on the unaffected side and Aa is the amplitude on the affected side. Normative data were obtained from 52 healthy volunteers (23 women) aged between 22 and 76 years (36.7±2.4 years, mean±SD; median=32 years). Lt: left, Rt: right.

Fig. 2

Brain MRI of the patient with medial medullary infarction. A: Diffusion-weighted axial image disclosing acute infarction in the right medial medulla, which extends from the pyramid to the medullary tegmentum. B: Follow-up T2-weighted axial image also shows infarction in the corresponding area of the acute infarction shown on A. C: MR angiography revealing diffuse narrowing of the right distal vertebral artery (arrow) and focal narrowings in the left vertebral artery (arrowheads). MR: magnetic resonance.