Tysabri is a medication given intravenously every 28 days.
Tysabri works in MS by connecting to a molecule (an adhesion molecule) and then does not allow the movement of the active immune cells into the brain and the spinal cord.
Side effects: increased risk of infections and potentially liver effects and blood counts effects requiring monitoring blood tests regularly.
Progressive Multifocal Leukoencephalopathy = PML which a major brain infection triggered by the JC virus. The virus is named on the first patient that presented with this infection. About 50-60% of the general population has been exposed to this virus and developed antibodies to it based on a normal immune response. People that have been exposed to the virus and their immune system is compromised by any reason are at higher risk to be sick with the virus. PML is a severe infection and the usual recovery is poor.
There is a blood test to check for the presence of the JC antibody. If patients have a positive test (positive antibody) their risk to develop PML is higher. The risk is higher as you stay on the Tysabri infusions longer. The risk in the first year of the infusions is very low. People with negative test that is they were never exposed to the virus have a very small risk for PML. People may convert from negative to positive therefore the test for JC antibody is repeated usually every 6 months.
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