The fact that the number has gone up is likely a result of longer lives, but also an increase in diagnoses of MS. No one knows why MS is on the increase, but it is. The fact that the number has “only” gone up by 20,000 is likely to do with the fact that people die: for every one new MSer, there will probably be one who’s died. It will probably also have something to do with population dynamics. MS is normally diagnosed in early adulthood. Increase the number of adults in a population, increase the incidence of MS.
If a disease has an approximate incidence of 1:1000, one can expect a population of 65m to have approximately 65,000 people with that disease. However, the UK has a higher than average incidence of MS thanks to dodgy genes and dodgy weather. So we come in at approximately 100,000.
The DWP does not have data on who has MS. Why would they? When I applied for DLA, I put down 5 conditions. Which one should they record me under? The DVLA wouldn’t either because not everyone drives and not everyone tells them.
And why would PCTs have data on who has MS? As Tina says, it’s not a notifiable disease. And even if someone paid someone to look through every (hand-written!) medical file in the country they still wouldn’t know because then they’d have to check who was still alive, who was still living in Britain, who hadn’t had their diagnosis changed, etc.
So, what about going forward? Should these data be captured? Ideally perhaps, but only if someone has a bottomless pit of funding. First of all you’d have to pay for the software, then the hardware, then the people to use it all, then the people to use it forever after because it would need to be constantly updated. And how do we account for all those double/triple/etc entries? And now multiply that for all the different conditions out there - it wouldn’t just be a matter of checking for MS; we’d have to do it for everything. And then what would we do with the data anyway? Would it justify all that expense?
Epidemiologists have tried and tested methods for estimating the incidence of medical conditions. It’s not necessary to literally count how many people have something - there’s an established science that does it without that level of cost or effort.
That’s where the figure of 100,000 comes from. I see no reason to distrust it. Why would I? It’s probably right!