A multicenter, non-interventional study to evaluate the disease activity in Multiple Sclerosis after withdrawal of Natalizumab in Portugal.

Natalizumab (NTZ) is very effective for treatment of relapsing-remitting multiple sclerosis (RRMS), its use is mainly limited by safety issues. Discontinuation of NTZ is associated with recurrence of disease activity (reactivation and rebound). The best strategy for subsequent therapy and the predictive factors for recurrence in such patients are areas of active research. We aimed to evaluate predictors of reactivation in a multicentric study. Multicentric retrospective observational study in five portuguese MS referral centers. Demographic, clinical and imagiological data were collected in the year prior, during and in the year following NTZ discontinuation. Predictors of reactivation and rebound after NTZ suspension were studied using a multivariate Cox model. Sixty-nine patients were included. They were mainly non-naïve patients (97%), with a mean age of 29.1 ± 8.3 years at diagnosis, and a mean age of 37.2 ± 10.3 years at NTZ initiation. The mean annualized relapse rate (ARR) previous, during and after NTZ was 1.6 ± 1.2, 0.2 ± 0.5 and 0.6 ± 1.0, respectively. The median EDSS before, during and after NTZ was 3.5 (IQR 3.3), 3.5 (IQR 3.5) and 4.0 (IQR 3.8), respectively. The median number of infusions was 26.0 (IQR 12.5) and the main reason to NTZ discontinuation was progressive multifocal leukoencephalopathy (PML) risk (70%). After NTZ suspension, reactivation was observed in 25 (36%) patients after a median time of 20.0 (IQR 29.0) weeks. Reactivation predictors in our sample included NTZ suspension for reasons other than PML (adjusted HR = 0.228, 95% CI [0.084- 0.616], p = 0.004), ARR before NTZ (adjusted HR = 1.914 95% [CI 1.330-2.754], p < 0.001) and a longer disease duration at time of NTZ initiation (adjusted HR = 1.154, 95% CI [1.020-1.306], p = 0.023). Rebound occurred in 5 (7%) patients after a median time of 20 (IQR 34.5) weeks. Significant predictors of disease reactivation in our cohort were discontinuation of NTZ for reasons other than PML risk, higher disease activity before NTZ treatment, and longer disease duration. Our study provides valuable data of portuguese patients after NTZ withdrawal.

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