--small fiber neuropathy is hardly rare; it is the most common type of neuropathy from diabetes and a large majority of "idiopathic" neuropathy sufferers have predominantly small-fiber involvement.

There well may be a link between small fiber neuropathy and fibromyalgia--but a lot of that would depend on what one's criteria for fibromyalgia are (a subject that is still in considerable dispute among doctors and researchers).

Small fiber neuropathy, by definition, involves the small, unmyelinated nerves that subsume the sensory sensations of pain and temperature, and also most autonomic functions. There is no muscle involvement with small fiber neuropathy, as it is the larger, myelinated nerves that ennervate muscle. However, some think that muscle knots or trigger points can tighten and compress small fiber nerves that pass nearby them, leading to neural symptoms.

The muscle involvement reported with fibromyalgia (myo means "muscle") makes it unlikely that small fiber dysfunction is the primary or only mechanism involved in the condition. It is likely multifactorial and would certainly involve larger, myelinated nerves as well.