Update on PML cases
3rd February, 2011
According to recent information released by Biogen Idec in January 2011*, there have been 85 confirmed cases of progressive multifocal leukoencephalopathy (PML, a viral infection of the brain that can lead to death or disability) among people who have used Tysabri® (natalizumab), after it became available for prescription in July 2006.Of these cases, 44 occurred in Europe, 36 occurred in the United States, and 5 occurred in the rest of the world (one of these cases is in Australia).
As of the end of September 2010, 75,500 people worldwide have used Tysabri® since it was introduced. According to data released by Biogen Idec, based on the 85 cases, the overall risk of PML is estimated to be 1.06 per 1000 patients (95% confidence interval: 0.85 to 1.31 per 1000 patients).
Cases of PML have occurred in both men and women who had been given infusions of Tysabri® every four weeks for a duration ranging from one year to three and a half years, with an average of two years.
Typical symptoms associated with PML progress quickly and can include:
- personality or behavioural changes
- changes in thinking, memory, and orientation leading to confusion
- onset of seizures, clumsiness or progressive weakness on one side of the body
- disturbances of vision
If individuals taking Tysabri® experience new or unusual symptoms, they should contact their prescribing neurologist immediately.
Of those who have developed PML, 19 out of 85 have died (as of January 7, 2011). The degree of disability in the survivors is a wide spectrum: at the milder end, some have recovered enough to return to work, and at the other extreme, some are confined to bed, requiring extensive assistance with activities of daily living, and others were in between this range.
There are rigorous procedures to both monitor for PML and deal with cases. When PML is suspected, Tysabri® infusion is halted and removed from the patient with the blood-cleansing treatments of either plasma exchange or immunoadsorption. The best hope is then to reconstitute a person’s immune responses.
During the aftermath of PML, as the immune system begins to recover, a condition called IRIS (immune reconstitution inflammatory syndrome) usually occurs. According to the prescription label information, appropriate treatment of the associated inflammation should be undertaken.
New Tests: while there is no test that can predict who is more likely at risk for developing PML, researchers from Biogen Idec and Elan Pharmaceuticals published results on a new blood serum test that would detect antibodies to the JC virus. (The presence of antibodies indicates that a person has at some point been infected by or exposed to the virus.) In December, 2010, the company submitted an application to the Federal Drug Administration in the USA (FDA), proposing updated product labelling to include anti-JC Virus antibody status as one potential factor to help determine an individual’s risk of PML. The FDA has not yet approved the update.
Biogen Idec Australia provides a monthly update of information on PML cases to registered neurologists in Australia.
*Note - much of this information has been sourced from a recent posting on the National MS Society (USA) website.
Tysabri® is a registered trademark of Elan Pharmaceuticals.