Ocular vestibular evoked myogenic potential (VEMP) reveals subcortical HTLV-1-associated neurological disease

Abstract

Introduction: Vestibular Myogenic Evoked Potential (VEMP) evaluates vestibuloocular and vestibulospinal reflexes associated with posture. Purpose: To compare cervical and ocular VEMP in individuals with HTLV-1 associated myelopathy (HAM) and with HTLV-1-asymptomatic infection. Materials and Methods: This cross-sectional study included 52 HTLV-1-infected individuals (26 HAM and 26asymptomatic carriers) and 26 negative controls. The groups were similar regarding age and gender. Participants underwent ocular and cervical VEMP that were performed simultaneously. The stimulus used to generate VEMP was a sound, lowfrequency toneburst, intensity of 120 decibels normalized hearing level (dB nHL), bandpass filter from 10 to 1,500 Hz, with 100 stimuli at 500 Hertz (Hz) and 50 milliseconds (ms) recording time. An alteration in the electrophysiological waves 3 P13 and N23 for cervical VEMP and N10 and P15 waves for ocular VEMP was compared between groups. Results: Cervical VEMP was different among the groups for P13 (p=0.001) and N23 (p=0.003). Ocular VEMP was similar for N10 (p=0.375) and different for P15 (p=0.000). In the HTLV-1-asymptomatic group, 1(3.8%) individual presented changes in both ocular and cervical VEMP, while in HAM group, 16(61.5%) presented changes in both tests. Conclusion: Neurological impairment in HAM was not restricted to the spinal cord. The mesencephalic and thalamic connections, tested by ocular VEMP, were also altered. Damage of the oculomotor system, responsible for eye stabilization during head and body movements, may explain why dizziness is such a frequent complaint in HAM. Authors' summaryHuman T-cell lymphotropic virus type 1 (HTLV-1) infection is endemic in Brazil and can cause HTLV-1-associated myelopathy (HAM). This neurological disease progresses slowly and, within ten years after its onset, can confine the patient to a wheelchair. Changes in HAM inflammatory characteristics can subsequently occur in the cortex, subcortical white matter, cerebellum, and brainstem. In the present study, we used the electrophysiological test Vestibular Myogenic Evoked Potential (VEMP) to evaluate the thalamic, brainstem, and spinal neural connections. This test evaluates the peripheral and the central vestibular pathway and has been used to test the postural reflexes involved in the control of one's balance. The VEMP from 4 the oculomotor muscles demonstrated that a subcortical impairment occurs in HAM and can also occur in the asymptomatic phase of HTLV-1 infection. 1 Introduction 2 The Human T-cell lymphotropic virus type 1 (HTLV-1) infection affects 3 approximately 5-10 million people worldwide [1]. The majority of the infected 4 individuals remain asymptomatic throughout their lives [2]. The host genetic and 5 immunological factors seem to be related to the development of HTLV-1-associated 6 diseases [1,2].7The range of neurological manifestations of HTLV-1-associated myelopathy 8 (HAM) includes not only the spine, with the classical motor limitations affecting 9 the lower limbs, but also the autonomi...