--is meant by "bilateral lesions"? Are we talking evidence consistent with spinal nerve root problems, spinal cord problems (in both cases MRI's would be in order), or something more peripheral?

I will say that the B12 level is concerning. Usually don't see levels that low in younger people unless they are vegan/strict vegetarian or have some autoimmunity that would result in it, such as pernicious anemia or celiac, and you should be tested for both.

Problems with spine or nerve root issues can produce symptoms exactly mimicked by more peripheral conditions, which is why I often recommend the following rather comprehensive list of tests for neuro problems (so you can compare what you've had and track over time):

Liza Jane's Neuro Lab Sheets