Seems like you've got the picture together pretty well -- as you said, it's a neurological disorder where the central nervous system is malfunctioning, signals aren't getting through to the gi tract, and when that happens, all sorts of things in the gi tract can go awry, including the bowel problems you're experiencing.
There are lots of ailments that aren't by themselves diseases, but are indicators of something else gone awry. Like, in MS, spasticity isn't in itself a disease, but is a sign that the signals from brain to muscles isn't working right, and the muscles are contracting. Or like a fever isn't a disease, but a signal that there is some disease somewhere in the body that causes it.
The challenge for the doctor, now, is to figure out WHICH central nervous system disorder it is that is causing your problems. Is it MS, or something else, which is causing the signals from the brain to the gi tract to go awry? I don't know what other disorders can cause that...but presumably (hopefully!) your doctor will be able to tell you what she learns from the results of all your testing.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....