This is a prospective study which will be conducted in an educational medical hospitals in Sari, Iran.Adult patients with diagnosis of multiple sclerosis compatible with 2017 McDonald criteria and history of treatment with rituximab at least 3 times( 18 month) , enrolled to this study.Demographic patients' characteristics, including age, sex, vital sign, past medical history, drug history, will be recorded. Disease duration prior to rituximab, total rituximab dose, prior immunomodulatory drugs, Adverse drug reactions, the time interval between the last rituximab infusion and need for intravenous immunoglobulin replacement therapy and infections are recorded. Moreover, we will assess IgG and IgM levels, VZV titer at before rituximab administration and 6, 12, 18, months following the initiation of next dose of rituximab.
