Demyelinating diseases of the central nervous system in children are characterized by the complexity of differential diagnosis and require an integrated approach using laboratory and instrumental studies. The clinical observation of a child with gradually progressing neurological symptoms and the presence of focal changes in the brain demonstrates the difficulty of differential diagnosis between demyelinating disease, neuroinfection and hematologic disease (hemophagocytic lymphohistiocytosis), which initialized with CNS damage. The article presents the tactics of etio-pathogenetic treatment of a patient during differential diagnosis with the use of cytoflavin in complex therapy as a multi-factor drug that allows to stabilize the patient's condition.