According to one article I read somewhere. I'll have to search for it. Small Fiber Neuropathy damage can be seen with a skin biopsy, but they have to look using an electron microscope to see the damage to the small nerve fibers. Normal microscopes will not see the small nerves to see the damage.
Small Fiber Neuropathy was mentioned in an article regarding a person who developed EM after flying on a trip. The only thing that person had as a past medical condition was treatment for Anxiety and Depression, which was some time before they developed EM. As nerves and Neurotransmitter agents pass through the body and nerves are sending signals, either extra signals, pain signals, and even sensing pain and other things, it's easy to make assumptions as lay people about things that seem to be co-incidence and think, maybe that's a sign. For example the article talking about a guy who had SFN and EM mentioned he was treated for Anxiety and Depression in his past, but it didn't state how long his drug treatment was for that and he developed EM when he was young. My mother was being treated for Anxiety and Depression for years and also was very sensitive at times. Does she have heightened nervous reactions. Supposedly she didn't have SFN if the abnormal skin test not showing abnomal morphology cells, in her test meant anything. But I don't know if they actually looked at the skin plug tests using an electron microscope and looked at the small fiber nerves. It would seem she doesn't have small fiber neuropathy, but at times she was sensitive, and she would show more side effects to drugs, perhaps that's a sign. Do SFN patients react to drugs side effects more? Just a question for those who have it?
She also has some kind of large fiber nerve damage with 50% reduction in nerve velocity studies. So everyone can be different. As a catch all primary EM being inherited may be proven in the future to be all genetically linked, but I don't know if that has really been proven yet. I think some primary EM cases that have no other known cause, especially with the young have been found to be related to the gene mutation. It seemed like it was under 5% of the known EM cases where EM just appeared without a known cause. Maybe we should call EM without a known cause "sudden EM" or something to give it a different definition from the narrower primary definition some seem to be putting on the genetic version.
I wonder if drugs that pass the brain blood barrier that can affect the brain and nervous system can affect nerves in the hands and feet more and damage them. So drugs that are given for Anxiety and Depression which affect the brain, might affect and create a side effect causing EM. I wonder if that was the case with some who have taken nerve medications and developed EM afterwards. But I don't know if many have had that. Sometimes people get nerve pills for other ailments until the real source of the ailment is found. And then they may get additional side effects and damage from the nerve pills. This of course is just speculation about the side effects and how they may affect a minority of patients.
Some late night speculation on my part.
It's probably really difficult to get a plan together and have all the tools necessary to actually test and figure out what is going on with many patients out there who have EM.
For example with my mom's EM, certain foods and stresses can trigger it. Heat always triggers it, activity making the heart beat more and causing more work can trigger it. Calming the system down, lower the blood pressure may help, pain killers may help, some nerves blocked may help, but others won't at all. For my mom. It's almost like we have to drug her and put her into a very low functioning state, where the body is "cold" and there is no blood flow to get relief. How strange is that. Sugars, salts, heck most things that taste interesting can trigger a flare. She may weigh the pain vs pleasure of a small addition of something to her meal, based on the pain she might get from a flare trigger. So how can one even test and figure out what is going on with her or any EM suffering patient. They can do basic tests, but they can't really test the overall system or even know what tests need to be performed to figure out what is wrong. There are tests of course to see if you have large fiber damage, nerve velocity tests. And there are tests to test a plug in your skin to see what happened to the small fiber nerves. There is sympathetic nerve blocks, and radioactive bone density screening (once thought to be the best test, but not always accurate) for sympathetic nerve feedback damage RSD. Etc. There are tests to determine if you have pain from small sensations like a small brush going over the skin of your foot. These are all general tests. But how do they measure the dynamic interactions over time, what causes a flare, and what is happening first. For example how do they know it's an autonomic system failure or malfunction vs. blood flow vascular disease? There are a bunch of tests they can perform, but usually the tests, tell us "what it's not". They rarely tell us "what EM is", and that is the problem. It's often a case of elimination. And that of course makes it a long drawn out process.
By the old definition of Primary EM, meaning EM without a known cause is still used, I think only 5% of the patients with "primary EM" have it from a genetic defect. We used to say it's primary without a known cause, if we didn't know what the cause of the EM was. It's not secondary to another disease that can be treated. If Primary EM is genetic EM and we know it's from Genetics, then it's not caused by another disease, so it's primarily EM, it's genetically caused. So Genetic EM is primary EM, but people who have EM which is their primary disease may not all have it from Genetics. They have EM with an unknown cause or origin. Maybe it's a number of things and triggers that are triggering an overactive sensitive system? Maybe that's all EM is, a dysfunction.
In the case of my mom, I recently bought a FLIR cameras. I can photograph her flare. There was a case where RLS patients who had burning feet were tested with flir heat images and they tested them and photographed their flares compared to a normal persons flare and recovery from heat. And the RLS patients had EM like flares, from RLS. And their feet were evenly heated. Likely from mass muscle activity in the foot causing heat, my theory here . . .okay. But the control normal patients had uneven heating and measurements in their feet. I'd think the foot would be normal and have temperatures that were uniform for a normal person, but according to that study the normal people had uneven foot temp measurements. Which I find strange. Maybe they had a gradient of zones of temperature differences which would seem to match what I see on my "normal feet". Now my mom when she has a flare she has hot areas in parts of her feet but cooler areas in other parts of her feet, this for some flares. Other times the entire foot is hot, but there can be variations. This is strange. When my mom had "perhaps an abnormal suppression" with a tibial nerve block done on 12-30-2015 her entire foot on the blocked side had a more or less even temperature. Perhaps that is abnormal, but it being low at 75 or 76 degrees caused no pain. One part of her toes registered at 85 degrees without pain, but the nerve block blocked pain signals. By blocking pain signals the temperature of the foot was even. The other foot had temperatures much higher.
Her pain and feet can be high even with relatively normal temperatures, which seem normal to a normal person. So her feet will have swelling and pain when my feet would still be comfortable. She also at times has patches of cold on her feet which is reminiscent of some discussion of cold feet symptoms. But this only happens at times as a result of chilling of the feet and in the past year when a muscle relaxer was added to the mixture of drugs she was taking. Some pills, like Metropolol caused pain hot flares to move into her upper body and torso and she felt hot blood flow in her skull in a hospital stay while on Metropolol. So this is just our little experience as an example. How can doctors test and know what caused EM. Some of the causes may be more known and others may be speculative.
Let's think about it for a moment:
For example:
1. What if EM is caused by blood pooling up due to loss of circulation in your feet. This would be like the small blood vessels being plugged up, as in the case of diabetes. A vascular surgeon can do a doppler flow. One did on my mom and said her circulation was great and much like an 18 year old. And my mom's an old lady.
2. What if it's a case of the nerve thresh hold that is nerve messages regarding pain being misread and that is due to damage in the nerves in the spinal cord area. That might be triggering some kind of strange message thresh hold, which is much more sensitive than normal. Like being very ticklish, but your ticklish to heat. Maybe that's what SFN is doing? Then the nerves are sending some kind of signal that results in feedback to the brain which responds with pain or the autonomic nerves are sending more blood for the "problem" a kind of autoimmune disorder or damage to the autonomic system.
3. What if it's due to sympathetic nerve damage that is causing pain to be send down the sympathetic nerves. That's known as RSD, but perhaps some variation of that could be happening and a sympathetic nerve block might help in that case.
4. What if it's due to a person having their nerves die, large fiber neuropathy, which is causing the blood vessels to not respond correctly or sending bad signals of pain. Is the pain first, or the blood flow first? Is the blood causing pain, or the pain perceived with a normal vascular system? Also remember pain can cause a rise in blood pressure, high blood pressure might be a secondary thing from your EM, not the cause. In my mom's case her blood pressure during high pain flares can go way down simply by chilling her feet with quick chilling techniques, ice packs or cold water immersion.
5. What if it's from high blood pressure. Maybe the person had low blood pressure and low heart rates, but then their heart beat and blood pressure rose. This may have caused more heat to be generated and then pain results from blood being sent down but not returning.
6. What if it's a blood flow issue in the small blood vessels?
7. What if it's caused by a deposit of sugar on the nerves and when your sugar is lower those sugars are not on the nerves, so more nerve issues happen when your sugar level is off.
8. What if it's due to vascular dilatation issues, with blood being sent to a false injury?
9. What if it's due to some kind of drug reaction, like Serotonin syndrome? That would be very short lived as those kinds of side effects are quickly resolved as the drugs are changed. I was wondering and worrying about this because five things my mother takes can affect Serotonin, and she had symptoms that might match that, or could be just do to drug withdraw from taking less medication that adjusts that. She had for example tremors, temperature and heat issues, this perhaps due to a Vitamin B12 shot, which can help some with EM but make others with EM to have worse symptoms. She also had less pills that day and sometimes if she misses her pills that suppress the pain she will have pain flares. She also had Ativan withdrawals or so that seems to be the case. So every test has to have a lot of variables looked at and measured and hopefully a lot of constants during the test remain the same, when your testing a change in a drug. It's very hard to make tests for example when someone with EM is taking a ton of drugs for symptoms, because the drugs can affect the results of the tests. (This Point is kind of a tangent and covers to much and has a lot of speculation.)
10. What if it's from a secondary disease or chemo treatment that can be resolved and that stops the problem? In those cases it's considered secondary EM, because when the primary disease that caused the burning feet to happen, the EM is resolved. You can get EM from chemotherapy drugs that affect your nerves, if your dying from cancer and have chemo the rest of your life, you may have EM the rest of your life.
11. Fungal infection. A fungal infection might cause it? Well perhaps not, but some may confuse the two. A fungal infection is kind of like Mushroom poisoning which is a kind of fungus. I suppose if the fungus infects the nerves and damages them, it could cause EM.
12. Vitamin B5 deficiency. WWII vets in Japanese prison camps had EM from a lack of vitamin B5.
13. Pox Virus that affects autonomic nervous system. In China a pox virus caused EM in Chinese students. They have rare strains of viruses that can be given to test animals who develop EM from the virus.
14. Some people with "RLS" or Restless Leg Syndrome can develop Burning feet from the build up of energy from muscles moving in the restless leg, or it would seem that is the case.
15. It's "normal" for a human to push hot blood to their extremities at night to lower their core temperature. This might be from a kind of evolutionary or (created design) trait or characteristic of the human organism. We might have a tendency to push blood to the outer hands and feet at night in order to cool our core body temperature.
15. Typical neuropathy. A typical diabetic neuropathy which may have been talked about briefly in one of the earlier points, can have burning and shooting pain symptoms and have burning feet at times. I think this is a kind of "cold neuropathy" where the nerves are dying and people loose sensation and feeling, and they may get shooting pains and hot reactions, but normally the foot is cold and purple more often. That is the common neuropathy. I think that is the polar opposite of a "hot Neuropathy" but this is just my guess. Kind of like EM being due to Axiom damage to the nerve but MS being the destruction of the outer nerve sheath. I think the two major conditions, one being more numbing and cold and the other being super sensitivity and being almost always hot and extra excitement or feeling. I think they are polar opposites and likely respond to different therapies. But this is just my speculation as a casual observer.
(Note some of the points mentioned above are speculation some are based on articles I've read, but my memory and speed at typing this post might not include all factual points, so take some of my post with a grain of salt.)
All these things are some examples of EM like problems or things that might cause it. How can we tell the cascade of what is happening and the triggers. Genetics might have a part of the answer, but I don't know if we can say it's all genetically predisposed. I'm not putting down genetics or genetic diseases or the things and role it can play. There is just a ton of things that the body is doing and all kinds of interactions. Obviously the EM suffering patient has unfortunately gone far from the fold of normalcy, due to their rare illness. It can take a long time to figure out what may be causing it and even once one starts figuring out what it was, there may be little in the way of a cure or way to cope with the problem.
It seems that common neurological problems, remember if it's from the nerves, it can be from anywhere in the nervous system. I could be anywhere from the brain, down through the entire nerve trunk to the area of the pain. Nerve issues can develop when some nerves die and others "make up signals" to fill in the lack of signals as well.
With many neurological problems something has attached itself to the nerve and damaged it.
What about some kind of damage to the neurotransmitters. Think about it? Side effects from drugs that are altering the neurotransmitters (like nerve pills) can alter brain chemistry to get some "good" desired effect. What if the effect is not so good, and what if the side effect or damage damages the nerves in some other part of your body. The same drugs we might be using to treat nerve issues might be damaging nerves in other parts of our body, but this is just my guess as a layman from various articles I've read. Neurologists and others can test you and give you more specifics to your particular disease. The web can provide some nice clues and hints and be helpful to doctors with a vast array of knowledge. Hopefully more information that is verified and wide ranging as surveys can be provided to give better clues from things like the Tea website. To make it easier for doctors to figure out how to treat the different forms of burning feet and narrow down better treatments for different patients.
I find the hypersensitivity to pain and heat interesting. I wonder if most EM suffering patients have hot foot issues a lot of the time and virtually no cold feet. Or is there a cold foot version? It seems there are two types at least, and perhaps dozens or even hundreds of variations. There are Neurological tests that a Neurologist can give as mentioned in the thread which can narrow down and perhaps get rid of some of the things which might be the cause. That test takes about an hour to perform, and many doctors won't spend the time with a patient to do the entire test.
Some people also having tests done find them difficult and painful. My mother complained about the pain from the nerve testing after having the nerve velocity tests performed. She said she could feel the needles as if they were still in her from those tests, even years afterwards. I don't think this was a constant thing, but I think it was something that did bother her. Lightly brushing my mom's foot might cause great pain, even a light brush from a piece of paper could cause her to cry out. A person with RSD in comparison might feel pain via the sympathetic nerves and feel burning in their chest, like a sparkler burning constantly inside their chest cavity. A RSD patient might not even be able to stand the cold air from a fan and would say the cold air feels like fire. So there are nerve based conditions that are even more dreadful than severe forms of EM, believe it or not.
For the EM suffering patient some medications of course that help others cause their own EM to flare.
It seems anything that excites the metabolism and blood flow, heart beat elevation, extra activity, even emotional excitement and stress can trigger flares. And flares can exist with a RLS foot like issue, or without it. At least that's how my mother's EM is and how many others report EM. EM seems to be worse with certain medications or treatments and this can vary from patient to patient.
DISCLAMER to MY LONG POST HERE.
I'm of course speaking as one who has seen EM in my mom who has a chronic form of it, so my viewpoint is limited by my experience and the limited knowledge I've read from the net. I often don't have time to search and read a lot, even on these forums. So my comments here (sorry for the long post and lack of proofread), is mostly from my own experience and can't be taken as a summary of all the facts and evidence found in the posts of others. I'm just a guy witnessing EM in my mom's case.