MechanicallyInclined, I have secondary progressive MS and have been using a TENS unit off and on since March 2010. It was given to me by a doctor who has been working with me to help me recover the use of my shoulder from atrophy in the trapezius and related muscles after stents were implanted in my IJVs in September 2009. I think your question relates primarily to the symptoms you are trying to treat, not to the question of MS. Your doctor is probably the best qualified to say whether there is any concern related to your MS. This layman (that's me) says there is probably no concern.
CCSVI Procedure 9/16/2009 at Stanford
Stent in left and right IJVs
Copaxone and Ampyra user
Botox Bladder Injections