What test for to Find The Source of My Small Nerve Neuropathy?

Hello @kumye, welcome to Mayo Clinic Connect, a place to connect with others patients like you. If I understand what you are asking, you haven't been diagnosed with small fiber neuropathy yet but you have neuropathy symptoms and are asking what tests are used to diagnose small fiber neuropathy. Here is some information from Mayo Clinic that might answer your questions.

-- Small Fiber Neuropathy: Diagnosis and Treatment - Insights:
https://news.mayocliniclabs.com/2022/04/13/small-fiber-neuropathy/
Do you mind sharing a little more about your neuropathy symptoms?

I've already been diagnosed I was just wondering if there are any tests that recommend why I have it. Over time it has gotten worse over the last two years but it consists of burning, tingling and overall burning at first in my legs and full body but over time it stopped. And since then every day randomly i'd get a random sensation along with it become easier for my limbs to fall asleep/ feeling lost little by little. It gets worse when I wakeup and eat high carb/sugary meals but I stopped that a while ago. and now im losing sensation everywhere in my body and it has progressed really far and it gives me anxiety and stress everyday. But this is full body neuropathy and mostly effects my sensory nerves.

I have no medical training or background but I think finding a specific cause can be difficult for most people. There are a couple of sites I really like for learning more about neuropathy that you might find helpful.
-- Neuropathy Commons: https://neuropathycommons.org/
-- Foundation for Peripheral Neuropathy: https://www.foundationforpn.org/

I shared my neuropathy journey in another discussion here - https://connect.mayoclinic.org/comment/310341/. A few years ago I made some lifestyle changes to see if I could help reduce the numbness I have in my feet. Since I've been in the pre-diabetic category most of my life and it runs in my family, I've always been worried about getting diabetes but it's never progressed that far. I recently learned about the Metabolic Syndrome and most doctors don't mention it but I fit that category as do most people that are pre-diabetic. So, I started a low carb healthy fats and intermittent fasting diet. It has helped me lose a lot of weight and feel better but the jury is still out to see if it will help my neuropathy. Here's more information on the Metabolic Syndrome if you are interested:
-- The Metabolic Syndrome and Neuropathy: Therapeutic Challenges and Opportunities: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3881591/
-- Metabolic syndrome as a risk factor for neurological disorders
https://pubmed.ncbi.nlm.nih.gov/21997383/

This video by Mayo is good for discussing causes and tests: https://youtu.be/HXJ--wPIhNc

Hi John,

Thanks for the hint about metabolic syndrome. My expanding waistline during covid isolation/inactivity fits this picture.

Otherwise, in my search for answers, I recently came across a published paper on B6 toxicity which might be of interest:
https://www.sciencedirect.com/science/article/pii/S221343442030013X
It used a very small cohort but even so found some individuals for whom B6 quickly accumulated to toxic levels.
(It did not accumulate for most volunteers.)
Another interesting point to note from the study is that the normal method of testing for B6 in the blood does not actually test for pyridoxine but instead for PLP. It was the pyridoxine that accumulated and caused problems.

John

Have you seen this one on B6 toxicity? This is one of the better sites I’ve found that puts it all together in an easy to understand way.

Vitamin B6 Toxicity:
http://www.easy-immune-health.com/vitamin-b6-toxicity.html

Thanks for the link. I'm struggling a bit to reconcile the analysis on the easy-immune-health site with the results on the paper that I linked.
They both indicate that it is the PLP in the blood plasma that is normally used to assess the level of B6. OK. But the research paper says that the anomaly occurs only with the measured pyridoxine, not with the measured PLP. It was the pyridoxine that accumulated with repeated supplementation. I think I have that right.
Beware, layman speculating:
Perhaps the accumulation is because there is insufficient cellular PLP and therefore the body's control system thinks there is not enough B6 and so cuts down on the excretion of the excess pyridoxine. Hmmmm. But then the question arises, is the nerve damage due to the excess pyridoxine or to the PLP deficiency in the cells? The fact that very high doses of pyridoxine can induce neuropathy seems to favour the former explanation. If the neuropathy in this case were due to a PLP deficiency then high doses of pyridoxine would have no effect.

I think that my problem with the the easy-immune-health analysis is that they seem to be saying that if you have too high levels of PLP in your plasma then the solution is to take more PLP which will (somehow?) reduce the toxic level of PLP in your plasma. It really only makes sense if they were measuring the plasma pyridoxine instead. Perhaps the plasma measurement of B6 was actually of PLP plus pyridoxine?

Good to know not all B6 is that interesting. That version of B6 testing seems easy to get inside Mayo as long as your doctor orders the right one: https://www.mayocliniclabs.com/test-catalog/overview/42360

Here are a few more references on B6...

-- B Vitamins for Neuropathy and Neuropathic Pain
https://www.omicsonline.org/open-access/b-vitamins-for-neuropathy-and-neuropathic-pain-2376-1318-1000161.php?aid=90896
-- B6 section it explains -- too much or too little gives neuropathy
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4199287/
-- FDA Safety Alert: Biotin Can Affect Medical Test Results
http://cle.clinic/2G6Mp4y
-- NIH - Nutritional Neuropathies
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4199287/
-- Vitamin B6 Toxicity Revisited: A Case of Reversible Pyridoxine-associated Neuropathy and Disequilibrium. (P4.021)
http://n.neurology.org/content/90/15_Supplement/P4.021

Again, thanks for the links, The last one was particularly interesting in that they were measuring serum pyridoxine (not PLP) and that there was significant recovery after cessation of the pyridoxine supplementation.
My own particular interest in B6 toxicity is a result of my flawed attempt to follow the 525 protocol. This may serve as a warning to others.
In order to get sufficient B vitamins (roughly 50mg each of B1, B2 and B3 as in the protocol) I found a B-50 complex. This also had 50mg of B6 which is not part of the protocol. I quickly checked the usual medical websites where the advice was (and is) that B6 deficiency can cause neuropathy and that B6 is not toxic even in large doses of well over 100mg taken for many months. Bad advice.
Unfortunately my PN worsened over the few weeks when I thought that I was following the protocol and I now think that this MAY have been due to B6 toxicity. So I am now back to following the protocol but without the B6.
One ray of hope which could be an extremely rare symptom: While taking the B6 I also developed recurring bouts of very hot and itchy toes, sometimes even waking me up in the middle of the night. Since I stopped the B6 about two weeks ago the hot feet problem has disappeared. Maybe just a coincidence but it gives me some hope that recovery is possible.