VEP result, heat and when lesions show up on MRI


My brain MRI from august showed a possible area of damage to my left optic nerve but I have had a VEP done now which is normal. I currently have problems with my vision if I have a hot bath and at other times where it goes cloudy or just not right. I also had an episode 10 years ago where I lost vision in both eyes for a few days. Is it possible to have a normal VEP and still have had optic neuritis or other vision involvement in MS. Also does anyone know if any other neurological conditions other than demyelinating ones lead to increased symptoms with hot baths and other heat? Finally if it were to be MS obviously I would expect lesions to show up on MRI at some point. Does anyone have any experience of them not showing up at first and how long it took for them to show up. How long after a first MRI would be reasonable to do another? Sorry for all the questions. Just so confused everyone including the MS specialist seems to be expecting to find that I have MS but dont seem to be getting any evidence.



I’ll do my best…

  • It is possible to have normal VEPs, but still have abnormal vision. No test is perfect, plus “normal” just depends on a set of measurements which define most of the population. Perhaps yours were particularly fast before the ON, so the ON has left them now slower, but still officially normal? It is also possible that the vision loss 10 years ago was not due to a vision problem per se, but perhaps something interfering with the visual pathways? This is probably highly unlikely, but (e.g.) a pituitary tumour can press on the optic chiasm and cause blindness. Could there be something self-healing that might do something similar, but once healed, leave the visual pathway intact? I really don’t know - but an ophthalmologist should.

  • Uthoff’s (the heat/vision thing) can happen in any demyelinating condition. There are actually quite a lot of these. MS is the obvious one, but there is also NMO (Devic’s), AMN, leukodystrophies, and even things like vitamin B12 deficiency.

  • There is a small but significant percentage of MSers without visible brain lesions on MRI. Most would go on to develop lesions, but not all do I believe. How long it takes for lesions to show is impossible to say, sorry.

  • The best time to have another MRI is probably when something new has happened.

Sorry, but I can’t remember what other symptoms you have? It is possible to get ON on its own. If you have other symptoms, then have you had the blood test for NMO done (a spinal MRI is needed too) - people with NMO often have clear brain MRIs (I’m assuming yours was clear)? Also, have you got a family history of Addison’s or any other relations with eye or neuro problems or a love of salt? If so, then you should maybe have a look at AMN. Most neuros don’t test for it.


Karen x

Thanks Karen. You are always so knowledgeable. I have had the blood test for B12 which was normal and also the one for NMO which was also normal. We have no history of Addisons or neuro problems. The AMN information seems to say it is only young men. My MRI of brain without contrast in august showed a possible increase signal to left optic nerve. I have also recently had a full spine one which showed a syrinx in the thoracic area but the consultant says this will not explain most of my symptoms. I started with a dizzy spell in february. I then had many symptoms from shooting pains in my head which then left a prickly sensation, tingling in toe, achey and stiff leags, off balance, reoccuring tingling/numbness in tongue and lips and cognitive issues. The main ongoing symptom though has been fatigue with a lightheaded foggy headed feeling. I have suffered with bouts of fatigue and funny head on and off for a long time but thought it was normal. Thankfully it seems to be much much better now and only returns generally when tired. If I have a bath I am left weak, lightheaded and funny vision.

I have to have regular MRIs to monitor my syrinx so was thinking that maybe lesions would show up then rather than have to have a lumbar puncture which is obviously what the MS specialist wants to do next. One more question how definitive an answer is LP? I am trying to work out if it is worth it or not for me. For some reason it absolutely scares the heebie jeebies out of me. You would think as a nurse I would be a bit better about it lol.

AMN also happens in women, but it’s pretty rare so not usually considered. The reason I mentioned it is that optic nerve demyelination is fairly common, but not everyone has brain lesions. It is unlikely if there’s no family history though. LPs are about 90%, but I’ve seen numbers from 80s to mid 90s. The LP isn’t just a test for MS though - it might provide info for other possibilities so it’s definitely worth doing if you are stuck. Make sure you get someone who knows what they’re doing though - and that they use a small gauge needle (reduces the headache risk). It’s really not bad if it’s done right. If they’ve ruled out everything but MS then I guess it’s worth factoring in what happens if you have a positive or negative LP result though. Maybe you’ll still need the MRI confirmation, in which case it’s less important to get the LP. Tricky! Karen x