I'll tell you my experience. Ive had MS for 20yrs now. Last October I had a really big flare and the mri showed no new or active lesions. Had another really big flare in December this time I could barely walk, but could not walk on my own, had to have a walker or I just fell. Even with the walker I could barely move. MRI showed no lesions on the spine. My neuro told me just because the mri didnt show a lesion or active lesion, doesnt mean its not there, just means it didnt "light up" on the mri.