This is just my opinion (I am a retired pediatrician with newly diagnosed MS). From what you told us you have already established a pattern! I don't know why your doctor isn't proceeding with that information. Is this a neurologist that's holding off? If it is MS, and it well could be, it is important to "label" the patient, that is make the diagnosis, as early as possible. In the majority of cases of MS, the most common type is called Relapsing-Remitting and this can usually be treated with Disease Altering Medications. These meds (usually a form of Interferon) have been shown to slow the progrssion of the disease and to slow the rate at which you accumulate disability. They don't treat or improve problems that are already established. They take several months to begin having an effect, so MS specialists try to begin them as soon as possible after establishing a diagnosis.
The diagnosis of MS can be difficult to make, but it isn't always. Some people have very classic presentations and can be diagnosed shortly after their first symptoms. When you had your visual problems was it diagnosed as "optic neuritis?" Were you examined by an Ophthalmologist? If so, this is the single most classic presentation of MS. It is treated by IV steroids. You also can have optic neuritis without having MS.
The diagnosis of MS requires evidence that there have been attacks on the white matter (the myelinated part of the nervous system) in at least two different places and that attacks have occurred at at least two different times separated by at least a month.
You describe the attack of visual problems which resolved. (one attack in the visual nervous system, the optic nerve - maybe) the next "attack" was of leg weakness. Was this both knees? Bilateral symptoms are less characteristic of MS, but not impossible. That problem also went away or "remitted." If the weak knees "attack" was more than a month apart from the eye attack it could be counted as two attacks in different areas, separated by time.
Then there is the MRI with lesions both in the brain and the brain stem. Two other different sites of attack, and there was a change with increased lesion activity in the second MRI which may indicate that this was merely an evolving lesion (not a new one) or a new one right beside it. AND the MRI's indicate the lesions look like areas of demyelination. That is what MS does - it attacks the nervous system causing demyelination.
Do you have any abnormalities on your neurologic exam? Sensation defects, reflexes, balance problems, etc. A neurologic defect provides even more evidence of an attack in even other locations.
Depending on the answers to some of the questions I think you might have already established enough criteria to make the daignosis, especially if that first attack was daignosed as optic neuritis. If no diagnosis was made then you should have an evaluation by an opthalmologist called "Visual Evoked Response." This test can determine if there was a prior episode of optic neuritis.
Finally, if someone EXPERIENCED in diagnosing MS is still unsure, the next appropriate step is a spinal tap, which can provide confirmatory evidence of MS or other related diseases. People are often afraid of spinal taps and there are people here on this forum that have had problems, but ten's of thousands of taps are done every day and it is the small, small minority that have difficulty.
Have you had all the blood tests to workup "myelopathy?" This is necessary because the diagnosis of MS also requires that no other disease is causing the symptoms. This should be done immediately, if it has not been done.
There is a very nice website, that a non-MD has written about MS for people who need information. It explains this information in more detail. Copy and paste this link into your browser:
http://www.mult-sclerosis.org/
If you would like to, I would like to hear the answers to someof the questions I've asked. I hope this post has not frightened you. I looked at it like this during the two + years that I was losing function and couldn't get a diagnosis - I knew that SOMETHING was really wrong. I wanted to know what. Not knowing (but having a strong suspicion) was far worse than getting the diagnosis. Then I at least had something to deal with. Less than 25% of people with MS ever end up in a wheelchair. It is not a death sentence. AND I am not diagnosing you with it. I can't. I'm just putting together your information. Also here is the blurb that I wrote up about my road to diagnosis.
http://www.medhelp.org/forums/Multiple-Sclerosis-Support/messages/23.html
Please write me back, Quix