 In particular spinal DCS sDCS has been proven to modulate Nociceptive Withdrawal Reflex NWR, an objective and sensitive tool to explore pain processing at the Spinal Level and recommended by European Federation of Neurological Society EFNS to evaluate the analgesic effect of treatments. In this order of view the investigators objective is to investigate sDCS efficacy in MS neurophatic pain treatment applying validated clinical scales, neurophysiological acquisitions and specific biological marker dosages. 