Toward European harmonization of national myasthenia gravis registries: modified Delphi procedure-based expert consensus on collectable data by Slioui, A, Tammam, G, Vanoli, F, Marina, AD, Vohanka, S, Gilhus, NE, Moroni, I, Leite, MI, Piehl, F, Antozzi, C, Pini, J, Stascheit, F, Attarian, S, Santos, E, Verschuuren, J, Canonge, L, Garcia, J, Perriard, C, Cortés-Vicente, E, Mantegazza, R, Meisel, A, Sacconi, S