Recurrence of disease activity after repeated Natalizumab withdrawals.

Natalizumab (NTZ) is extremely effective in reducing disease activity in multiple sclerosis (MS) patients but its long-term use is associated with the risk of progressive multifocal leukoencephalopathy (PML). Thus, many patients discontinue NTZ and, after drug withdrawal, most of them face disease reactivation despite immunomodulant (IMD) start. The aim of this study was to evaluate the efficacy of different therapeutic strategies in preventing post-NTZ disease recurrence in a small cohort of patients that underwent repeated NTZ courses. 15 patients underwent two distinct NTZ discontinuations and started IMD after first withdrawal and a second line therapy (mainly fingolimod, FTY) after the second one. They were followed with periodic clinical and neuroradiological evaluations. All patients showed disease reactivation after first withdrawal and 13 out of 15 relapsed after the second one. In both the occasions annualized relapse rate (ARR) significantly increased as compared to on-treatment period (from 0.03 to 1.5 and from 0.26 to 1.71) with no differences between the two NTZ-free periods. Likewise, the mean number of Gd enhancing lesions increased both times to similar values (3.1 and 2.9). Median time to disease recurrence was comparable (4.7 and 5.7 months, p = 0.57). This study demonstrated recurrence of disease activity after two distinct NTZ discontinuations despite the treatment with IMD or more aggressive therapy, when used according to recent safety recommendations. Therefore, we need different therapeutic strategies to cope with the risk of post-NTZ disease recurrence and a "bridging strategy" with an earlier switch to second line drugs should be taken into account.