I have researched and studied ms extensively since I was diagnosed with it in june 1998. All my readings show absolutely no connection between the two. Ms does not cause strokes; the damage that is incurred in a person with ms concerns their nerve (neural) pathways.
The insulation around the nerve pathways gets attacked by "something" which causes scar tissue to build up in that attacked spot (sclerosis means "scarring"), blocking messages from the brain that would ordinarily go down that nerve pathway. In turn, the lack of whatever the brain's message was may cause something bad to happen to the body.
For example, if the hand is reaching toward an open flame, with the assistance of the nerve pathways, a feeling of heat is recognized by the brain. In return, the brain sends out the message by means of the same or a different nerve pathway to withdraw the hand because an injury is imminent. If that message is blocked because of scar tissue short-circuiting the warning, the person could end up with a nasty burn.
Ms does not affect the vascular system, unless it is in an indirect way as with the hand in the above example. Strokes are caused primarily because of blood clots in the blood vessels in the brain. When the blood clots, there is no blood flowing past that spot and that means oxygen is not getting carried to the "heart" of the brain where it is needed to carry out normal brain function (including vision, movement of limbs, speech, and so much more). The amount of the damage the stroke causes is dependent upon where in the brain the blood clot occurred; different body functions are controlled by different areas of the brain.
25 is extremely young to suffer a stroke. Has your doctor found a specific cause for it? Why specifically are you scared that you have something wrong besides the stroke? Since you have already had the primary test (the mri) that usually rules out or confirms ms, has a neurologist read the mri? It is possible to have ms without anything showing up on the mri yet. Another test is usually performed if a diagnosis of ms is suspected. It's called a spinal tap (or "lumbar puncture") wherein a sample of the fluid in your spinal column is tested for certain antibodies and other data. The spinal tap can be negative also and you can still have ms. In my case, my mri showed "lesions" on my brain (which corresponds to attacks upon my nerve pathways, but it does not tell which ones) but my spinal tap was negative for ms. Yet I was diagnosed using my symptoms and the positive mri.
What kind of doctor have you dealt with already? If it was a neurologist, i'd suggest talking to him specifically about what the mri showed in relation to the symptoms you are having now. If you aren't satisfied by his answer or if he just brushes you off, i'd certainly get a copy of your mri and take it to a second neurologist, preferably a ms specialist, to get a second opinion. Ms is notoriously hard to diagnose and can sometimes take years to pin down, but there is no reason you have to suffer the way you are in the meantime. There are medications to help out with your symptoms, which a competent neurologist would give some consideration to.