A "copy" WILL be of use. They will either send the tissue "block" (suitably processed so very thin sections can be prepared for microscopy), and / or tissue sections already prepared, on glass microscope slides. Either way the sections which will be seen here in the UK will be virtually identical to the originals because they are taken from the adjacent tissue (within a fraction of a millimetre).
(As for the suggestion of multiple sclerosis ( MS), I can understand why they considered that, as it's in the same group of conditions as ADEM, but you've been reassured by the UK specialists that they don't think it is MS).
I'm glad to have helped in addition to the great support given by other members![]()