I declined, but still went on to be diagnosed.
In my opinion it probably did delay diagnosis by about six months, because it’s my impression he probably would have diagnosed right away, if I’d had it, and it had been positive.
Instead of which, I had to wait six months for a second MRI scan, which showed new activity, and allowed him to be sure enough.
On the other hand, if I’d had the LP and it was normal (which can happen, even if you do have MS), we would have been no further forward, and I’d have had it for nothing (one of my objections to having it - although a positive result greatly increases the evidence for MS, it cannot categorically prove it - whilst a negative result does not mean the person cannot have it, and therefore may not help the investigation whatsoever).
Personally, I wasn’t that bothered about the six months, as I believed, and still believe, I’d already had MS (or whatever “it” turned out to be) for years.
However, I know many people are desperate for a diagnosis, and my: “six months is nothing” line of reasoning may be a little unusual, to say the least.
Obviously, it wasn’t a very nice six months, but I was pretty resigned to it by then that it was MS - just a couple of scares when it briefly looked as if it might be something even worse! If you’re convinced you’ve already been ill for years, the concept of “acting fast” is a bit lost on you - six months no longer seems like a big deal.