Date Published: July 12, 2018
Publisher: Public Library of Science
Author(s): Ludimila Labanca, Júlia Fonseca de Morais Caporali, Sirley Alves da Silva Carvalho, José Roberto Lambertucci, Anna Bárbara de Freitas Carneiro Proietti, Luiz Cláudio Ferreira Romanelli, Paul Avan, Fabrice Giraudet, Bárbara Oliveira Souza, Kyonis Rodrigues Florentino, Denise Utsch Gonçalves, Pedro de Lemos Menezes.
Vestibular-evoked myogenic potential triggered by galvanic vestibular stimulation (galvanic-VEMP) evaluates the motor spinal cord and identifies subclinical myelopathies. We used galvanic-VEMP to compare spinal cord function in individuals infected with human T-cell lymphotropic virus type 1 (HTLV-1) from asymptomatic status to HTLV-1-associated myelopathy (HAM).
This cross-sectional study with 122 individuals included 26 HTLV-1-asymptomatic carriers, 26 individuals with possible HAM, 25 individuals with HAM, and 45 HTLV-1-seronegative individuals (controls). The groups were similar regarding gender, age, and height. Galvanic stimuli (duration: 400 ms; intensity: 2 mA) were applied bilaterally to the mastoid processes and VEMP was recorded from the gastrocnemius muscle. The electromyographic parameters investigated were the latency and amplitude of the short-latency (SL) and medium-latency (ML) responses. While SL and ML amplitudes were similar between groups, SL and ML latencies were delayed in the HTLV-1 groups compared to the control group (p<0.001). Using neurological examination as the gold standard, ROC curve showed an area under the curve of 0.83 (p<0.001) for SL and 0.86 (p<0.001) for ML to detect spinal cord injury. Sensibility and specificity were, respectively, 76% and 86% for SL and 79% and 85% for ML. Galvanic-VEMP disclosed alterations that were progressive in HTLV-1-neurological disease, ranging from SL delayed latency in HTLV-1-asymptomatic carriers, SL and ML delayed latency in possible HAM group, to absence of VEMP response in HAM group. The worse the galvanic-VEMP response, the more severe the myelopathy. Galvanic-VEMP alteration followed a pattern of alteration and may be a prognostic marker of progression from HTLV-1-asymptomatic carrier to HAM.
Human T-cell lymphotropic virus type 1 (HTLV-1)-associated myelopathy (HAM) is a chronic inflammatory disease that occurs in approximately 3% of HTLV-1-infected individuals [1,2]. HAM affects mainly the lower thoracic spine [3–5], which leads to progressive postural and gait impairments .
In the present study, galvanic-VEMP disclosed an altered EMG response of the inferior limb in HTLV-1-infected individuals that otherwise were considered asymptomatic carrier. For the SL and ML components of the EMG wave, a greater latency delay was associated with a greater motor impairment.
The worse spinal cord damage in HTLV-1 infection, the worse galvanic-VEMP response, characterizing a gradient that ranged from a delayed latency in the HTLV-1-asymptomatic carriers and individuals with possible HAM to an absent response in individuals with confirmed HAM. Galvanic-VEMP is a promising tool for improving the early diagnosis of HAM and might be used for the following-up of patients under future therapeutic strategies.