Reader response: Progressive multifocal leukoencephalopathy after fingolimod treatment.

Abstract

Berger et al.,1 based on the Novartis safety data lock point of August 31, 2017, reported that the risk of patients developing progressive multifocal leukoencephalopathy (PML) after treatment with fingolimod remains low. Addressing the question of PML risk is of particular importance in light of the recent increase of fingolimod-treated patients with this devastating iatrogenic complication. Nevertheless, the results presented here are lacking, mostly because the risk calculation is made with the overall population treated by fingolimod, without taking into account some specific risk factors. The risk of PML is clearly age- and treatment duration–dependent. Indeed, 13 of 15 patients with PML were >45 years old at time of diagnosis. All but one had a >24-month treatment. Four additional PML cases are described to date (19 PML cases as of May 7, 2018) according to an email from Novartis in April 2018. Despite the restricted number of cases that may limit some statistical calculation, the PML risk in patients treated for >2 years may be more frequent than currently estimated. If the risk assessment also included JC virus (JCV) antibody status and age, the PML risk will undoubtedly increase in this specific population. Therefore, particular attention must be paid to patients positive for JCV antibody, >45 years old, and receiving fingolimod for >2 years. Additional studies addressing this risk should at least include age, treatment duration, and JCV status, keeping in mind that patients treated with fingolimod deserve a specific approach that does not necessarily match patients treated with natalizumab.