An editorial notes that the two main limitations of this study are related to its observational design, and need consideration in the interpretation of the results. Firstly, the absence of magnetic resonance imaging (MRI) data, both at baseline and during follow-up, a major determinant of treatment choice at baseline and a factor which can drive treatment switch during follow-up. Thereby, this lack of data is likely to have introduced biases. Secondly, the results may have been affected by the different pattern of discontinuation of alemtuzumab vs. the other drugs included, with the authors noting that treatment persistence of alemtuzumab would not be comparable with that of the other drugs assessed in this study. However, the researchers mitigated these differences by matching for length of follow-up and doing a sensitivity analysis based on an intention-to-treat principle.