Of the available disease-modifying treatments for multiple sclerosis, Tysabri (natalizumab) has arguably been the most controversial to date.  The reason for this controversy is a condition called progressive multifocal leukoencephalopathy or PML.  Any patient who is trying to decide whether Tysabri is the right medication for personal use, she/he must balance the risks and benefits and how those might fit into his lifestyle or circumstances.

Of the 79 Tysabri patients who developed PML, 16 patients have died to date.

The number of Tysabri patients who have developed PML (progressive multifocal leukoencephalopathy) has reached 79* as of December 17, 2010 says Biogen Idec, Inc.  The company also reports that an additional death among Tysabri/PML patients has occurred, bringing that total number of cases to sixteen. (*updated Dec 17, 2010)

"The number of PML cases is important because if the infection rate climbs too high, the drug's sales growth may drop. Regulators have said that they watch the cases, but have concluded that the benefits of the medicine to MS patients outweigh the risks.  The overall global PML rate is about 0.96 per 1,000 patients, a company spokeswoman said, which still falls within the 1-in-1,000 rate previously seen in clinical trials and implied on the drug's label. But the rate has been rising, and multiple Wall Street analysts raised concern about the trend on Wednesday as the MS market is becoming increasingly competitive."

Biogen reports that as of Sept. 30, 2010, there are 55,100 patients using the drug around the world and that approximately 75,500 patients have used the drug since its launch.  Of the 79 total cases of PML, 34 cases were in the United States, 40 cases were in the European Union, and 5 cases were in other areas.

"The most recent data update translates to a rate of 1.54 cases per 1,000 for patients on the drug for a year or longer, but rises to 2.05 per 1,000 for those on the drug for two years or longer.  Looked at another way, the rate is about 1.48 cases per 1,000 patients on the drug for between two and three years. The incidence is about 0.38 case per 1,000 patients in those using it for one to two years, and it is essentially nonexistent in patients using it for less than a year."

According to these growing numbers, the death rate of Tysabri/PML patients is at 20%.  I wish that we knew the condition of the other 80% of PML-affected patients.  It would be helpful to know how much PML has permanently disabled them.  Reports are limited.  The chart below shows the number of reported PML cases in patients using Tysabri, where they live, how many have died, and the percentage of deaths among Tysabri-PML patients.

What is PML?

Progressive Multifocal Leukoencephalopathy (PML) is a rare disease that damages myelin, the fatty substance which protects nerves in the white matter of the brain.  It is caused by an infection or reactivation of the JC virus in patients who have weakened immune systems due to disease (ie. HIV, Hodgkin’s disease, lymphoma), use of immunosuppressants (such as in transplant patients), certain kinds of chemotherapy, or medications for multiple sclerosis (ie. Tysabri/natalizumab), rheumatoid arthritis (ie. Rituxan/rituximab), or psoriasis (ie. Raptiva/efalizumab).