This is an observational cohort study utilising all available data from the Tysabri TOUCH (TYSABRI Outreach: Unified Commitment to Health) prescribing programme (US) supplemented with data from European Union (EU) multiple sclerosis (MS) registries to estimate the risk of PML and other serious opportunistic infections (OIs) among patients on Tysabri who have switched from newer DMTs (including fingolimod, dimethyl fumarate and teriflunomide) and the established DMTs (interferon beta and glatiramer acetate).~This study will provide cumulative data from its two components: a retrospective component (data captured prior to 01 January 2016) and a prospective component (data captured, and patients followed up, from 01 January 2016 through 31 December 2023; total prospective study duration of 8 years). All patients who switched to Tysabri from another DMT through 31 December 2020 will be included. The study will continue to follow-up patients until 31 December 2023 to allow for a minimal follow-up of 3 years.
The primary purpose of this study is to estimate the incidence of progressive multifocal leukoencephalopathy (PML) among patients who switched to Tysabri from disease modifying therapies (DMTs), including newer DMTs (including fingolimod, dimethyl fumarate and teriflunomide) and the established DMTs (interferon beta and glatiramer acetate). Researchers will also look to estimate the incidence of other serious opportunistic infections among patients who switch to Tysabri from newer DMTs (including fingolimod, dimethyl fumarate and teriflunomide) and the established DMTs (interferon beta and glatiramer acetate)