Progressive multifocal leukoencephalopathy and sphingosine 1-phosphate receptor modulators used in multiple sclerosis: an updated review of literature.

The incidence of PML appears to be extremely low in MS patients treated with S1PR modulators. Risk of PML increases with increase in duration of treatment with S1PR modulators like fingolimod, and increased age at the time of PML diagnosis is associated with worse prognosis.