Hi Debbie,
Sorry I don't know the answer to that. I think it is very individual how steroids work. I have used oral ones, high and low dosages. I have used them for a longer amount of days at times also.

I have had IVSM for 10 days at 1000 mg a day with no oral taper, or 5 days of 1000 mg alternating the dose up and down for a few days to knock the crapola out of a bad relapse.

Sometimes I found the steroids helped right away, other times it took months. Sometimes they take their good old time and I see improvement 6 months down the road. At what point it takes away the inflammation, and how long it takes to help heal the lesion, is different from person to person and flare to flare.

I have been told that my MRI looked good at one point. I said great! The MS Specialist had said that was because you just had steroids within the last 6 months. What he meant I don't really know. If I asked him every question I wanted to ask Him I would be in the office a week. Maybe ask you doctor or radiologist when you see him/her.
Maybe someone else has that information.
Lady