What can a lumbar puncture show if MRI is clear?

Hi all, I posted here a few weeks ago asking whether my symptoms could actually be MS related when I was referred to neurology to check for the possibility of a mass on my optic nerve. Since then I’ve been told my eye problems were probably optic neuritis and had an MRI that “showed no evidence of demyelinating lesions”, according to the copy of the letter sent to my GP. However the letter also says they will offer me a lumbar puncture at my next neuro appointment. So now I’m wondering whether this is worth agreeing to or not - what could the lumbar puncture tell the doctors that the MRI can’t? Is it really worthwhile if the MRI is clear? I’m a bit confused to be honest, I’m glad the neuro is taking it seriously but I got the impression the neuro exam didn’t show anything unusual either, so it seems odd that they’re even bothering and I don’t want to go through a nasty procedure and waste everyone’s time if it isn’t going to show anything useful. As damn annoying as my symptoms are, I’m quite happy to know it isn’t a brain tumour and just carry on suffering in silence til they progress to something debilitating (although the annoying electric shocks in my hands did actually trigger a spasm that covered me in my daughter’s jelly the other day). So is it worth it, or is the neuro just trying to keep me happy because of the long fight I went through to get the referral in the first place? Thanks x

If I were you, I would be asking the neuro exactly what will happen if the LP is positive/negative and why it is necessary, but fwiw…

If your symptoms and history suggest you might have primary progressive MS, a positive LP and lesions on either the brain or spinal cord is enough for a diagnosis.

If you are more likely to have relapsing remitting MS, a positive LP indicates a higher chance of having/developing it, however, a negative LP does not rule it out.

If the neuro is unsure of the cause of your optic neuritis, a negative LP would support a non-demyelinating cause, but I would suggest that VEPs would be a less intrusive way of testing this. If both the VEPs and LP were inconsistent with MS, then it would be pretty strong, but not conclusive, evidence that you do not have MS.

Ultimately, time will tell. If it’s MS, it’s unlikely to go into permanent remission. Same goes with other things. However, I think I would want to know what the neuro was thinking before I decided to wait and see, just in case one of the possibilities is best treated early.

One final thing: did you have cervical and thoracic MRI scans?

Karen x

Thanks Karen - I intend on asking the neurologist but just figured it’ll be easier to understand his answer if I’ve found a bit out about the possibilities beforehand! He didn’t mention VEPs in the letter but maybe he will at the appointment - do you have any ideas what an LP could show that a VEP couldn’t? My MRI was brain and cervical spine, not thoracic. I do get the electric shocks when I tilt my chin down, did I understand correctly from the other posts on here that this is something that’s usually MS rather than anything else?

VEPs only give information about the visual system. An LP shows all sorts of information that together with blood tests can distinguish between lots of different conditions. (There’s bound to be a wikipedia page about LPs - it might tell you about some of the conditions.)

The only reason VEPs would be better than an LP is if the neuro wanted to work out what caused your optic neuritis.

So both would be better than one, but if there was to be only one, I would say that an LP provides more information.