Risk of secondary progression in patients with highly active multiple sclerosis treated with natalizumab: a real-life study.

Background: one of the most important therapeutic goals in relapse-onset multiple sclerosis is to preclude conversion to secondary progression. Our objective was to determine the risk of progression associated with natalizumab treatment in an registry-based cohort of patients and to identify determinant factors.

Methods: Patients with relapse-onset multiple sclerosis from the Registre Lorrain des Scléroses en Plaques (ReLSEP) were included if they had received one infusion of natalizumab between 2002 and 2021. The risk of secondary progression was determined using a standardized definition and a multi-state estimator to account for the possibility of stopping natalizumab before progression, and analyzed with multivariate Cox models.

Results: 574 patients were followed up for a median of 6.7 years. Of the 304 who stopped NTZ before progression onset, the probabilities (95% confidence interval) to convert to progression after 1, 2, 5 and 10 years were 3.2% (2.0-4.8%), 5.3% (3.6-7.3%), 17.5% (14.3-21.3%) and 28.3% (23.7-33.7%), respectively. Discontinuation of NTZ during follow-up was significantly associated with an increased risk of conversion in case of no resumption of a highly active treatment thereafter (adjusted hazard ratio = 2.7; 95% confidence interval 1.5-4.9; p = 0.001). The use of such a treatment was associated with a lower risk of progression (adjusted hazard ratio = 0.42; 95% confidence interval 0.23-0.79; p = 0.007).

Conclusion: the risk of conversion to secondary progression associated with natalizumab treatment is relatively low but increases in case of natalizumab discontinuation in the absence of switch to highly active immunosuppressant.