Wednesday, 31 October 2012

Natalizumab PML Update - September 2012

"Apologies about not getting these latest figures to you. I have also included the presentation from Biogen-Idec for your information."

Natalizumab Safety Update September 2012 from gavingiovannoni

"As at the 5th September, 2012, there have been 285 reported cases of MSers with PML as a complication of natalizumab treatment. This is with a denominator of over 104,000 treated MSers worldwide or greater than 224,000 years of natalizumab exposure."

"The risk is presented for your to see and depends on whether or not you are JCV+ve, have had previous exposure to immunosuppressants and how many infusions you have had."

"In response to a question about how do you count the number of infusions you have had if you convert from being JCV-ve to JCV+ve. This is a difficult question as the switch could be due to the variability of assay or a real biological conversion due to infection with the virus. This is when a titre may help; i.e. if it is a low titre or low antibody levels to the virus it is likely to be due to the variability of the assay a so called false negative or positive result. In comparison, if the titre is high it is likely to represent a true seroconversion due to a new infection. I also would ask for IgM antibodies to the virus. These antibodies are made with an initial infection. If positive for IgM antibodies this would indicate a recent infection."

"If your JCV+ve is due to a recent infection I would start the clock from the previous negative sample; this is being conservative and assumes you became infected shortly after that negative test. If it is due to assay variability  i.e. low titre with no IgM antibodies I would not reset the clock and start counting from your first infusion; in other words you have been infected from the beginning. I would also assume the first test was a false negative result and the new test was correct. Why am I being so conservative? You don't want to down play the risks when the potential complications are so bad!. One in 5 people who get PML die from the infection and 90% of the survivors of PML have moderate or severe disability."

CoI: multiple


  1. Thank you, it was most clarifying.
    Of course there's a difficultie in distinguishing false negatives but my concern was really about what would happen if you were a true converter and you answered that...
    Congrats for the award by the way, well deserved :-)
    /Swedish Sara


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