--that you're showing up negative/normal for some of the nastier causes of peripheral nerve damage (such as autoimmune cross-reactivity due to neoplasm).

It is very difficult, when one keeps coming up negative/normal on these tests, to determine if one has an idiopathic small-fiber syndrome, or if one has some degree of central sensitization of central pain. Most cases of central pain do originate from some form of identifiable "smoking gun"--stroke, MS, combined subacute degeneration due to B12 deficiency--but it's certainly true there can be trophic changes to spinal neurons, especially in the spinothalamic, that can be very hard to detect. The chemistry of these reactions has become better known (interactions with Substance P, particularly), but try sampling that is spinal neurons without subjecting a patient to massive potential complications . . .

One of the neuros I've corresponded with at Hopkins about ganglioneuropathy (cell damage in the dorsal root ganglia) said, with typical neurologist humor, that finding such damage, or other trophic changes, awaits either better imaging techniques--or our autopsies, and I imagine that's true with a lot of Central Pain patients, too.