Long-term use of natalizumab in the treatment of multiple sclerosis is associated with risks and requires caution. In cases of discontinuation of therapy, it is necessary to remember the possibility of rebound syndrome and determine the optimal timing of switching from one drug to another to minimize risks. However, it is important to focus on the risk of developing progressive multifocal leukoencephalopathy, especially in patients with a history of immunosuppressive therapy, with anti-JCV (John Cunningham virus) antibody index of more than 1.5 and receiving natalizumab therapy for more than 2 years. Therefore, assessing the risk-benefit ratio of using a particular drug to treat multiple sclerosis is a complex but crucial step in choosing a therapeutic strategy for a particular patient. We present a clinical case of a patient with the development of rebound syndrome after discontinuation of natalizumab therapy when switching to another highly effective drug.

Keywords: immune reconstitution therapy, progressive multifocal leukoencephalopathy, rebound effect, natalizumab, multiple sclerosis