Tremor stability index: a new tool for differential diagnosis in tremor syndromes by di Biase, L, Brittain, J, Shah, S, Pedrosa, D, Cagnan, H, Mathy, A, Chen, C, Martín-Rodríguez, J, Mir, P, Timmerman, L, Schwingenschuh, P, Bhatia, K, Di Lazzaro, V, Brown, P