Tolebrutinib is a medication being studied for its long-term safety and tolerability in people with multiple sclerosis. This includes those with relapsing forms of the disease, as well as those with primary progressive or nonrelapsing secondary progressive multiple sclerosis. The goal is to see how well patients can tolerate the medication over an extended period and to monitor any potential side effects.

Relapsing Multiple Sclerosis – This is a disease where the immune system mistakenly attacks the protective covering of nerves, causing communication problems between the brain and the rest of the body. It is characterized by episodes of new or increasing neurological symptoms, known as relapses, followed by periods of partial or complete recovery. Over time, the disease can lead to a gradual worsening of symptoms and disability. The progression of the disease can vary greatly among individuals, with some experiencing frequent relapses and others having long periods of stability.

Progressive Multiple Sclerosis – This form of multiple sclerosis is marked by a steady worsening of neurological function from the onset of symptoms, without early relapses or remissions. It can be further classified into primary progressive multiple sclerosis, where symptoms gradually worsen from the start, and secondary progressive multiple sclerosis, which follows an initial relapsing-remitting course. The disease progression can lead to increasing disability over time. The rate of progression can vary, with some individuals experiencing a slow decline and others a more rapid deterioration.