Jesse,

As you have already surmised, I think the blood work was looking for other things, while the MRI was looking for evidence of MS (among other things). It is very common when somebody presents with symptoms that might be MS, to test their blood for all kinds of other things to look for evidence of Lupus, Rheumatism, etc. So on the whole, if all of those came back negative, but you had an MRI that looked like MS, they could use the combination as a diagnostic.

I am kind of curious why your docs would rule out MS with that radiological report from your MRI? Did they actually look at the MRI CD themselves or did they just read the report? I can see where they would say there isn't enough evidence from that MRI to call it MS for sure, but I also can't see how they would see that and rule it out entirely.