--small fiber neuropathy does not cause weakness per se, since the small, thinly myelinated and unmyelinated fibers are sensory and autonomic in function, not motor.

Given that, though, the sensory and autonomic disruptions can cause increased fatigue as muscles have to be used in different ways to compensate, and those might be interpreted as motor symptoms.

Since the small fibers do include pain receptors, there might be some overlap with fibromyalgia. Small-fiber sufferers generally don't have the pressure points that is associated with fibromyalgia, but many with either condition experience cramping.

There were a series of reports a few years back indicating that many people diagnosed with fibromyalgia may have small-fiber neuropathy in addition to, or instead of, fibro. (This may have something to do with the lack of consensus on just what constitutes a fibro diagnosis.) The following report was typical:

http://www.medscape.com/viewarticle/772864