AQP4 and myeloid sarcoma: Autoantibodies targeting theastrocytic water channel aquaporin-4 (AQP4) have emerged as a highly sensitive andspecific biomarker for the differentiation of NMOSD from MS, which is a crucialissue for an appropriate therapeutic choice.5 In fact, several MS treatments, such as interferon (IFN)-β, natalizumab andfingolimod, could lead to exacerbation of the NMOSD disease course, supporting theidea that NMOSD is distinct from MS and that NMOSD is dominated by humoralmechanisms.