--is just a subset of peripheral neuropathy, referring to preferential damage to the smaller, unmyelianted or thinly myelinated fibers that subsume the sensations of pain, temperature, and many autonomic functions.

It cannot be detected through standard nerve conduction studies or EMG's, as these only measure larger, myelinated sensory and motor nerves. Sometimes quantitative sensory testing or specialized autonomic testing, such as sudomtotor axon reflex testing, reveals it, but the current gold standard is skin biopsy to measure intraepdiermal nerve fiber density and condition. (There are also some other non-invasive methods being tested to detect small-fiber damage, such as refractive light microscopy, but these seem to have a way to go yet.)