As Karen has already said, there are defined rules, and she has given you enough leads to Google at your leisure, so you can have a read.
Personally, though, I don’t think it has anything to do with cost. I do, however, think you have an idiot, inexperienced neuro, who apparently isn’t familiar with the official guidelines in this country, and has inappropriately put forward a “cost” argument - apparently due to a mistaken understanding. I also think he’s acting totally unprofessionally by discussing a patient’s case with their relative, outside the consulting room. Now I know you may not mind, and even think it’s “handy”, as they work at the same hospital, but two wrongs don’t make a right. Realising the consultation hadn’t gone well, and attempting to explain himself to your wife, when they met in another context, is totally wrong. Smiling and asking: “How is your husband?” would have been acceptable, but not getting into the specifics of the case, and whether or not he agrees with them.
I would be absolutely incensed if this happened - even if the relative were one I trusted, and the information gleaned quite interesting. Because I’d be wanting to know: “What the heck were you doing discussing this, with my relative, when I wasn’t there?” It makes no difference that you “probably” wouldn’t have minded. The consultant has no right to decide this for you. Even if your wife attended your last consultation, it doesn’t prove that you gave ongoing permission for him to discuss the subject any time he happens to bump into her. For all he knows, you might have had a row last week, and filed for divorce! This is wrong.
Anyway, back to the LP. Yes, as Karen says, I was diagnosed without one. BUT, it’s important to understand that, LP or not, you still won’t be diagnosed until the evidence is sufficient. One scan result wouldn’t usually be enough, even where there are clear lesions. My initial scan results showed pretty “classic” evidence of MS: six lesions in my brain, and one in my spinal cord. This satisfied the “dissemination in space” requirement (lesions in two or more separate parts of the CNS). But didn’t satisfy the other diagnostic requirement of “dissemination in time”, because we couldn’t prove the lesions hadn’t all materialised at once, from a single episode.
So, what we did was wait six months, and scan again, at which time new disease activity was apparent. So my neuro could confidently say, at that point, that it was an ongoing problem, and not a one-off incident. This is necessary for an MS diagnosis. There’s no doubt my neuro would have preferred me to have a LP, if I’d given permission. But one of the reasons I declined was that it could come out negative/normal, and we’d be no further forward. I didn’t want to go through an invasive test that might not prove anything.
I’m not sure it would have resulted in immediate diagnosis, even if I’d had one, and it was positive. Because I think I’d still have had to wait for more lesions to show up, or for another clinical incident (relapse). This isn’t a money thing. It’s just to make sure you really do have it. I suppose money is one reason that might be important, but certainly not the only reason! Being diagnosed prematurely, and potentially receiving a WRONG diagnosis, is pretty serious for the patient too. If it came to a choice, I’d rather have a correct diagnosis than a fast one, but wrong.