The identification of autoantibodies to myelin oligodendrocyte glycoprotein (MOG) [53] and aquaporin-4 (AQP4) [39] in patients with clinical features similar to MS, have eventually resulted in the definition of separate diseases with important therapeutic consequences [44, 60, 61], but for most of the patients with inflammatory disorders of the CNS, the target of their autoimmune response has not been identified. Here, AQP4 is linked to myeloid sarcoma.