--is highly variable, in that some people get progressively worse, some plateau, some get better with good treatment, good blood sugar control if they are diabetic, immune modulating treatment if autoimmune mechanisms are involved, etc.

For small fiber neuropathy, it is to become muscularly debilitated, as the small fibers control sensory (pain/temperature) and autonomic (sweat, blood pressure) functions, and not motor ones. When one starts to get motor symptoms, one is not in the realm of pure small fiber neuropathy anymore, there must now be some large, myelinated fiber involvement. Still, if one is in constant pain, or has little autonomic control, that can be quite debilitating in itself. But small fiber neuropathy doesn't cause people to wind up in wheelchairs, generally.

The real key is to get an extensive enough workup (easier said than done in many areas, I know) to see if a cause can be determined, because many causes are treatable, at least to the extent that progression may be arrested.