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

IntroductionVestibular Myogenic Evoked Potential (VEMP) evaluates vestibulo-ocular and vestibulospinal reflexes associated with posture.\n\nPurposeTo compare cervical and ocular VEMP in individuals with HTLV-1 associated myelopathy (HAM) and with HTLV-1-asymptomatic infection.\n\nMaterials and MethodsThis cross-sectional study included 52 HTLV-1-infected individuals (26 HAM and 26 asymptomatic 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, low-frequency 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 P13 and N23 for cervical VEMP and N10 and P15 waves for ocular VEMP was compared between groups.\n\nResultsCervical 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.\n\nConclusionNeurological 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.\n\nAuthors 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 ones balance. The VEMP from the oculomotor muscles demonstrated that a subcortical impairment occurs in HAM and can also occur in the asymptomatic phase of HTLV-1 infection.