CSF analysis may show pleocytosis, neutrophils, eosinophils, and the absence of oligoclonal IgG bands that may differentiate seronegative NMOSD from other inflammatory CNS demyelinating diseases, including MS.18It is also essential for differential diagnosis of infectious diseases, particularly those endemic in Brazil (e.g., dengue,37, 38chikungunya, Zika,39CNS tuberculosis, among others.40The severity of NMOSD can be measured by serum biomarkers, such as serum fibrillar acid glycoprotein41or serum neurofilament light chain, as they indicate astrocyte damage during attacks.42 The gene discussed is NEFL; the disease is myeloid sarcoma.