What makes a lesion an MS lesion?


Earlier this week, I was diagnosed with MS.

It was a weirdly easy diagnosis. My hand has been numb for 3 months, I had an MRI and it showed lesions on both my brain and spine - around six. They’re certain enough they want me to go on a drug.

But I’ve read a lot of stuff since, and so many people are in limbo. Many people have MRIs that DO show lesions but then they’re not definitely diagnosed… even with way more lesions than me.

So, I don’t understand what made my lesions different and therefore so certainly MS.

I asked and was told it was to do with the fact that some of the lesions are old and some are new. But I still don’t really get it, because if other people have lesions and NOT MS, why do I definitely have it? I think maybe they’re in parts of the brain that definitely indicate MS… but does that mean other people’s are not??

if anyone can shed any light on this, that would be awesome.


the lesions need to be separate in time and space. that is the multiple bit. the sclerosis are the scars or lesions. i was diagnosed on just one mri and a lumbar puncture. also inflammation plays a part. 10 years into ms now and i have a vague understanding but not an outright knowledge. how are you coping with the diagnosis?

Had 2 bright spots on my brain but was told neither was indicative of MS and did not represent inflammation. Interesting question. Would love to know the answer too.

It’s the McDonald Criteria:

The lesions should be specifically demyelinating plus be disseminated in time and space. So be in different parts of the brain/spine and clearly show that they’ve occurred at different times.

So if you have lesions which are not caused by demyelination, ie caused by an inflammatory process whereby the myelin - the stuff that coats the nerves (always makes me think about electrical wiring with damaged plastic coating) is attacked and the nerves are affected, then it’s not MS.

And you could have a dozen lesions that are caused by demyelination but are not separated by time - that wouldn’t necessarily be labelled as MS either (unlikely I’m sure, with a dozen lesions, but still…)

The drug the neurologist wants you to have will be a disease modifying drug (DMD). Have a look at: It might help to be familiar with the various options. You probably won’t have a completely free choice, you’ll be offered maybe 3 drugs and be able to choose which one. An MS nurse should be able to help you with the drug choices.

It’s an odd time, having been diagnosed pretty quickly, there’s an awful lot to learn. Use the MS Trust information and/or the About MS tab at the top of this page. There are lots of information pages to help. And of course, so will we.

Best of luck.


Thanks for the comments everyone. What you’re saying makes sense I think, Sue. But now I want to know how a doctor can tell a lesion is demyelinating!

I don’t know. You’d have to ask a doctor I think!!