As the unconventional thinker at this website who believes that excess insulin (hyperinsulinemia) plays a major role in the initiation of MS, I always suggest people request that their doctor order a "fasting serum insulin test." Additional blood tests for cortisol, glucose, and the thyroid hormones is a good idea, too -- it is a good idea to establish the starting points.
Insulin thickens and stiffens the smooth muscles (some are found around the bladder, the intestines, and in the walls of blood vessels). In fact, I think some of the sensations we observe could be insulin's affect on these muscles -- our nerves are working just fine. An imbalance of insulin (an excess) can affect or be affected by levels of other substances such as cortisol, glucose, and thyroid hormones, etc., I believe.
But, please remember, these are MY ideas. I have found no expert who agrees with me yet.