Types of nerves
I have wondered too about the various involvements. I am sure there are multiple reasons. One, I think it likely that the myelin that surrounds the CNS nerves is a bit different from the myelin that surrounds the PNS nerves, although I have no real proof of this. The reason I think so is CNS myelin is made by oligodendrocyte cells, with one cell myelinating multiple nearby nerves, while PNS myelin is made by Schwann cells, with one associated with a single nerve. It seems likely that there are slight differences in the myelin from each type of cell, such that an attack on one type is not as efficient as an attack on the other. Two, the “porosity”, for lack of a better word, of the blood-brain barrier (that it CNS nerves) and the blood-nerve barrier differ. Some things may transit one barrier more easily than the other, leading to different attacks.
Autonomic nerves, which are part of the PNS and not the CNS, are responsible for the viscera, which includes the heart, lungs (and breathing by a feedback loop), bladder, and bowels. If someone has trouble breathing or with heart regulation and is known to have GBS/CIDP, the problem is likely a PNS problem and much less likely a CNS problem. My guess as to why this subset of the PNS seems to have less frequent involvement is that the nerves are shorter, so the overall damage is less significant.
Types of nerves
I hope that the olfactory involvement proves to be something other than truly olfactory. Here’s why. There are twelve cranial nerves. The optic nerve, the one that takes the signal from the retina and into the brain, is considered a central nervous system nerve. The olfactory nerve also is considered a central nervous system nerve. The other ten, such as those that control the eye, and the auditory nerve, are considered peripheral nerves. If you have either optic or olfactory nerve involvement, either you have an unusual presentation of CIDP or something else [I]may[/I] be going on.
Godspeed in sorting it out.