O papel do potencial evocado Miogênico Vestibular (VEMP) na avaliação da via vestíbulo-espinhal em indivíduos com Mielopatia associada ao HTLV-1, Mielorradiculopatia Esquistossomótica, Esclerose Múltipla e Doença de Ménière

Abstract

The clinical usefulness of the Vestibular Evoked Myogenic Potential (VEMP) has been studied for detecting vestibulospinal inferior tract involvement. The aim of this study was to investigate the alteration role of the VEMP for HTLV-1 associated myelopathy, schistosomiasis myeloradiculopathy, multiple sclerosis and Ménières disease. For each group, the exam was defined as normal or abnormal and correlated with the complaints: walk difficulty, tinnitus, hearing loss and dizziness. The reference values were defined based on normal subjects and validatedaccording to the literature. It was evaluate 126 individuals: 30 with absence of hearing or neurological complains and seronegative for HTLV-1 infection (control group); 52 HTLV-1 infected patients, being 35 asymptomatic, 10 with complaint of walk difficulty, but without HTLV-1 associated myelopathy and 7 with definite myelopathy; 12 with schistosomiasis myeloradiculopathy, 14 with multiple sclerosis and 18 with Ménières disease. In order to record VEMP, it was used 200stimulations in the frequency of 1Hz with intensity of 118 dB NA tone burst, bandpass filter of 10Hz-1500Hz, with register time of 60 ms. For the analysis of P13 and N23 waves, latency, amplitude, interaural and interpical difference were considered. The variation of the amplitude was controlled by the asymmetry index. In relation to the results, the age varied from the third to the sixth decades, 49 men and 77 women. VEMP reference values were: P13=13,66 (DP=13,10 -14,98) and N23=23,23 (DP=20,36-24,57), with average asymmetry index of 26,36%. For theHTLV-1 infection, VEMP varied according to the complaint of walk difficulty, being abnormal in 50% of the asymptomatic carriers and in 71% of those with complaint of walk difficulty with or without definite HTLV-1 myelopathy. The absence of evoked potential were associated with HTLV-1 associated myelopathy (P=0,01). In the schistosomiasis myeloradiculopathy, 66,6% of the patients had abnormal VEMP, predominating prolonged P13 and N23 latencies. In the multiple sclerosis, abnormal findings were seen in 92,8% of the cases, with predominance of prolonged P13 and N23 latencies. In the Ménières disease, P13 prolonged latency was the most common find and VEMP were correlation with hearing loss degree (P=0,00), being abnormal in 40% of the cases with little loss and 92,3% of the cases with moderate/severe loss. The present study confirmed that VEMP is agood test for evaluating the inferior vestibule-spinal tract and may be of usefulness for schistosomiasis myeloradiculopathy and HTLV-1 associated myelopathy, diseases not evaluated by this test, so far. Perhaps, it may distinguish the degree of medular injury, according to the pattern of evoked response: latency delay or absence of the response. The evaluation of the capacity of the VEMP in predicting improvement or worsening of the medular state in HTLV-1 associated myelopathy and the evolution of schistosomiasis myeloradiculopathy before and after treatment is proposed.