Hi Diggles, I know a little on this subject. Pml - Progressive multifocal leukoencephalopathy can be a side effect in a lot of these new drugs. Depends how they work. If they reduce the effect your immune system has on your brain and spine then you can get this brain disease cause by the John cunningham virus. I have had these worries but been reassured each time that the chances of contacting these are very very small. Even if you are jc positive. I was on tysabri for 10 years became jc positive in year 7 or 8 and was tested for my jc level so felt safer then. I took myself off tysabri due to this fear and feeling I wasn't looked after as well. My neurologist in Edinburgh died and so I moved my treatment to Manchester. ( I had been moved to South Cumbria but kept my treatment in Edinburgh) Manchester is very different to my ms experience in Edinburgh. Feel much less cared for. However now on kesimpta with possible similar side effects but no tests. Its all scary and I dont feel I have trust in my neurologist anymore. Speaking to my gp about this. Might try to move hospital again but I am on kesimpta so don't see anyone anymore anyway, even for annual check ups with the neuro. As long as I get an annual mri then I will possible stay. I would speak to your ms nurse/team about any worries you have. Hope my rambling helps.