The study will attempt to closely analyze Multiple Sclerosis (MS) patients after de-escalating or discontinuation of immunotherapy using clinical monitoring as well as digital and serological biomarkers in order to detect clinical progression or disease activity. As this is an observational study, it aims to closely follow-up on patients where the clinical decision to de-escalate or end treatment has been independently made. Specifically, we want to find out to what extent patients will show increased disease activity after de-escalation/discontinuation from high-efficacy treatment (HET) and which measurement method (clinical, digital, serological) retrospectively reflects the disease activity most closely or detects it most sensitively.