AQP4 and infection: The most common tests were infection serology (e.g. treponema pallidum, Borrelia burgdorferi, HCV, HBV, and HIV), autoimmune serology (e.g. antibodies against myelin oligodendrocyte glycoprotein, Aquaporin-4, Ganglioside, antinuclear antibodies, and anti-neutrophil cytoplasmatic antibodies), and exclusion of structural affection of the spinal cord using MRI (data not shown).