AQP4 and neuromyelitis optica: Correct diagnosis of a SLE–NMO overlap is important not only for the different disease course and prognosis compared with SLE-related LETM, but especially for the emerging and highly specific NMO treatment options, not established for SLE-related LETM—such as anti-aquaporin 4 antibodies, anti-VEGF antibodies, complement modulation, or IVIg.