Sounds like these neurologist are sitting back with the 'wait and see what develops' game.
MS sometimes will present itself with ON. Once ON subsides (pain and inflammation of the optic nerve)...it will not show on an MRI.
If I woke up in your shoes. I would find a qualified, well-versed MS specialist.
I told my neurologist that whatever I had...under no circumstances did I want him to tiptoe around me if it was a dx that he did not want to give...as I am stronger than I look...and that is exactly what happened...
Yes it is possible to have MS with 1 lesion (some docs prefer to see multiple ones)...others will wait to see what clinical findings would be. It's your health...demand answers!
Keep in mind there are other diseases that mimic MS and visa versa...have you been checked for Lyme disease (there are certain tests for that as well)
Best Wishes,
Zig