There is growing interest in the potential of eculizumab in severe autoimmune demyelinating neuroinflammatory disease, particularly anti-aquaporin 4-mediated neuromyelitis optica.8 In future cases of unexplained ADEM or AHLE, we suggest that clinicians investigate the presence of a potential complement regulation defect via extended complement assays (including complement function, activation products, and levels of CFI, CFH, and CFB). This evidence concerns the gene CFI and neuromyelitis optica.