Tysabri (natalizumab) is a medication primarily approved for treating relapsing forms of multiple sclerosis (MS), including relapsing-remitting MS (RRMS) and active secondary progressive MS (SPMS). It is not generally indicated for non-active or inactive SPMS. The key factor in its use for SPMS is whether the disease is “active,” meaning there are ongoing relapses or new inflammatory lesions visible on MRI scans.
Tysabri works by blocking a molecule called alpha-4 integrin, which prevents immune cells from crossing into the brain and spinal cord, thereby reducing inflammation and damage to nerve cells. This mechanism is particularly effective in forms of MS where inflammation is a driving factor, such as RRMS and active SPMS.
In the context of secondary progressive MS, the disease can be divided into two categories: active and inactive. Active SPMS is characterized by continued inflammatory activity, including relapses and new MRI lesions, while inactive SPMS shows progression without these inflammatory signs. Tysabri is approved and considered effective for active SPMS because it targets the inflammatory process that still plays a role in this phase. However, for inactive SPMS, where neurodegeneration rather than inflammation predominates, Tysabri is generally not used because it does not address the underlying mechanisms driving progression in that stage.
Other treatments have been developed and approved specifically for SPMS, including Mayzent (siponimod), which is approved for relapsing forms of MS including active SPMS, and Ocrevus (ocrelizumab), which is approved for both relapsing forms and primary progressive MS. These medications target different aspects of the immune system and may be more suitable for certain patients depending on their disease activity and progression.
In summary, Tysabri can be used in secondary progressive MS but specifically in cases where the disease remains active with inflammatory relapses or new lesions. It is not typically used for inactive SPMS, where other therapies might be more appropriate. The decision to use Tysabri in SPMS depends on careful clinical and MRI evaluation to determine disease activity and the potential benefit of targeting inflammation.
