Hi Lauren,
Unfortunately, having lesions in the frontal lobes and no where else still doesn't actually mean you can't have MS, because there is no single test to rule in or rule out MS with 100% confidence but that location and with none lighting up with contrast, doesn't specifically add any weight to support MS as a more likely causation either.
I had a look at the sx's you listed and abnormal test results.......
http://www.medhelp.org/posts/Multiple-Sclerosis/Finding-out-if-I-have-MS/show/2168061
.......and because you do have abnormal nerve conductor tests, there would be little doubt that something is going wrong some where, though I'm not sure MS would necessarily be the more likely answer, because your sx's and test results (so far) are not particularly suggestive of the cause being central nervous system.
Just a thought.......with your abnormal nerve testing on your legs and arms, it could actually be indicating the problem is with your peripheral nervous system, as i thought it was 'more common' in pwMS for these tests to be perfectly normal and it could be a red flags leading away from MS as the cause. It might be worth exploring that thought and looking up all the conditions that do cause abnormal results like you have, something might just stand out with your sx's too.
I did notice you didn't mention if you've had any visual testing or spinal MRI's and i think you're sx's would probably warrant some further tests, i definitely think its well worth getting because it could be important additional test evidence, all adding weight to what it is or isn't.
Cheers............JJ