Among patients with multiple sclerosis, discontinuing highly effective 
disease-modifying treatments can potentially lead to severe disease recurrence, 
especially cessation of natalizumab and fingolimod. Similar to fingolimod, 
siponimod is a sphingosine-1-phosphate receptor modulator that inhibits the 
egress of a lymphocyte subpopulation from lymph nodes. In the present case 
report, we describe a patient with MS who experienced substantial disease 
exacerbation after withdrawal from siponimod.