Some lesions are so tiny they don't show up for years. Also the doctor should write on the script, use MS protocol. the radiologist will sue a certain set of sequences, different the a regular head MRI. Also it should be in a closed MRI machine with a minimum of 1.5 telsa.

An LP can rule out other diseases. It doe not always rule in MS. If you have one lesion they may wait to see if you get more in another location. That will mean you had two attacks at different times, and spaced apart from the last one. Lesions do have many other diseases that put them there.

Location of lesion/s is important. I was dx'd before MRI's were around. Clinical exam, LP and history. Later on I had MRI's for ins purposes to go on DMD's at the time, so was Dx'd again.