neurologic symptoms

Hello--I am a 50 year-old woman with peripheral neurological symptoms. Three weeks ago, I developed a vertical itchy rash on my left thigh, about 6 inches long and an inch wide that went away after about four days.  At the same time the rash resolved (I was home by this time), I noticed a strange sensation on the bottom of my left foot, as if something was stuck on there.  Over the next several days, this sensation evolved into a growing tingling/numbness in both feet that began ascending up both legs and into my fingertips.  By the fourth day, the sensation had moved up to about waist level.  My internist felt this was due to a magnesium citrate supplement I had been taking for a few days for post-vacation constipation.  I stopped the supplement but the symptoms increased until.  I finally went to the emergency room (ten days after onset) and was admitted for tests and observation.  Everything was normal including lumbar puncture, reflexes, vision/eyes, muscle strength/coordination, Lyme's test, blood work, thyroid although Vit B12 was low and my T2 brain MRI showed "a few hyperintense lesions" indicating a possible demyelination process.  The ER neurologist has set me up with an MS specialist and was vague about the lesions accept to say that they were not in a typical positioning for MS and that they may have showed up for other reasons (a virus?) but he couldn't say for sure.  I have never had symptoms like these before and have been healthy my whole life accept for a teenage bout with with Mononucleosis that kept me out of school for a month.  Last year I contracted 5th Disease which I understand is a bit unusual for adults but this resolved after about 3 weeks.  I don't drink or smoke.  I am seeking input from you on these symptoms and am particularly curious if you think the vertical leg rash has anything to do with my current condition.  Thank you very much.--Ellen2075