Yes Dej - you should be proud of me
Here is some info I have found - the quotes are not necessarily direct, I got it all from this source, but only included relevant stuff that jumped off the page at me. If you follow the link, you may have to fish around a bit through links etc to find all the info I have used:
Most patients were treated with rapid removal of natalizumab from the circulation using plasma exchange or immunoadsorption. Nearly all of the patients (91%) developed immune reconstitution inflammatory syndrome (IRIS) and were treated with corticosteroids.
IRIS presented as new or worsening neurologic symptoms, tended to be severe, and usually occurred within days or weeks after rapid removal of natalizumab, the investigators note. "By 6 months post diagnosis, most of these patients had either recovered from IRIS or had started to recover from IRIS," Dr. Richman added.
Of the survivors followed up for at least 6 months from the time of PML diagnosis, one-third had mild disability, one-third had moderate disability, and one-third had severe disability, based on physician-reported Karnofsky scores. However, the investigators urge caution in interpreting the residual disability data, which were "probably confounded by disability attributable to underlying MS."
201 cases of PML have been reported among approximately 96,582 patients treated with Tysabri worldwide through January 4, 2012. The survival rate is now at around 71 %.
However, among those patients who have survived with at least 6 months of follow-up, most (87%) rate moderate to severe on the Karnofsky Performance Status Scale.
In addition, although the data show an 80% survival rate, this comes at a price, he said. "This is a miserable disease. If you got it, you'd probably rather be dead because there's no treatment for it — it destroys brain tissue. Eighty percent to 90% of people are highly disabled if they survive PML."
Anti-JCV Antibody Positive*
Tysabri Exposure 1-24 months <1/1,000
Tysabri Exposure 25-48 months 4/1,000
http://www.fda.gov/Drugs/DrugSafety/ucm288186.htm#hcp