Small Fiber Neuropathy: Genetics, Causes, and Possible Solutions

Key takeaways:

• In small fiber neuropathy, the tiniest nerve fibers break down and cause burning pain, numbness, odd sensations, or autonomic nervous system issues.
• Small fiber neuropathy is a type of peripheral neuropathy, but the symptoms can differ from what you would typically think of as neuropathy.
• Genetics can play a role in who is more likely to get small fiber neuropathy when triggered by certain factors.

Members will see their genotype report below, plus additional solutions in the Lifehacks section. Join today. 

What is Small Fiber Neuropathy (SFN)?

Nerve cells have long, slender fibers called axons that carry a signal from one nerve to the next. When the tiny peripheral nerve fibers are damaged in your skin or organs, it can lead to small fiber neuropathy, or SFN. [ref]

Symptoms of small fiber neuropathy include:

• Burning or aching pain usually in the feet or hands
• Tingling, numbness, and prickling sensation
• Dizziness or lightheadedness
• Heat intolerance and sweating
• Bloating and digestive issues

Small fiber neuropathy often starts with odd sensations in the feet or hands. Some people say ‘pins and needles’; others compare it to ants biting or itchiness. It can progress up the legs and arms and then throughout the body. The abnormal activation of these nerves can cause pain, diffuse sensations, and itching.

Small fiber neuropathy can also cause abnormal activation of autonomic nervous system functions like those in the heart, gastrointestinal tract, or bladder. Fatigue is common in SFN, which is thought to be due to the cardiac issues.[ref]

Small fiber neuropathy may also be involved in burning mouth syndrome.[ref]

Nerve types involved in SFN:

Nerves are categorized by type, including group A, group B, and group C nerve fibers. The group A and B fibers are myelinated, which means that they are insulated with myelin and carry the electrical impulse more quickly to the next neuron. Group C fibers are unmyelinated and carry information that is not needed as quickly, such as warm or cool sensations.

Small fiber neuropathy affects group C neurons and a specific subtype of myelinated group A neurons called Aδ.

• Type C fibers: unmyelinated, slower signal, sense diffuse pain, itch, and warmth.
• A-δ fibers: thin myelinated, faster signals, sense sharp prick pressure, cold, and specific rapid threat signals.

What goes wrong in small fiber neuropathy?

Small fiber neuropathy (SFN) is described as a structural anomaly of small nerve fibers along with degeneration of the nerve endings. It is diagnosed by a skin biopsy that looks at the tiniest nerve fibers. In SFN, the biopsy can show fewer than normal small nerve fibers in the skin, indicating nerve damage.[ref][ref]

The C-fibers involved in SFN transmit a more dull, diffuse pain sensation, which is a slower nerve conduction reaction. C-fibers are also involved in cold temperature pain (<5^oC) and warming skin (41^oC). Damage to the C-fiber neurons can cause temperature sensitivity and diffuse pain.[ref]

Sharp, pricking pain in SFN can be due to the involvement of the Aδ-fibers, which also respond to heat. The Aδ-fibers also respond to hair movement (skin hair movement), skin cooling (25^oC), heat pain (>45^oC), and excess stretching.[ref]

What causes the nerve endings to be damaged or degenerate? SNF can be caused by a variety of factors, according to research.

Causes of SFN can be classified as follows:[ref][ref]

• metabolic diseases (e.g., in diabetes)
• toxins (e.g., drugs)
• immune-mediated (e.g., autoimmune disorders, viral infection)
• genetic factors
• B-vitamin deficiency

SFN is heterogeneous, with not everyone having the exact same presentation. Subtypes of SFN can be classified by phenotypes including the areas affected and length of affected nerves.[ref]

Small fiber neuropathy and the autonomic nervous system:

It is easy to visualize how the damaged nerves in the skin on your feet or hands could cause pain, burning, numbness, or tingling. However, autonomic nervous system involvement can be harder to envision.

The autonomic nervous system involves all bodily systems that we don’t have to think about — heart rate, digestion, etc. We can divide the autonomic nervous system into categories: the sympathetic system (stress response), the parasympathetic system (rest response), and the enteric nervous system (digestive system).[ref]

Small nerve fibers control the following systems:

• heart rate variability with deep respiration (e.g., Valsalva maneuver)
• heart rate and blood pressure response to postural change (e.g., standing up after lying down)
• urine flow rate and feeling of need to urinate
• isometric exercise
• sweating
• skin wrinkling in water

Thus, damage to the small nerve fibers can cause disruption in heart rate, blood pressure, bladder irritation, lack of sweating, and a lack of skin wrinkling when in water for 30 minutes.[ref][ref]

How do nerves fire? A little background science.

Nerves send electrical impulses to the brain to activate specific brain functions. Here is an animated image showing how the electrical signal travels along the axon of a nerve cell.

Sodium and potassium ion channels open and close in response to a signal from another neuron (or a receptor). These ion channels allow positive or negative ions in or out of the membrane, thus changing the electrical potential. The buildup of charge then travels along the length of the axon to the axon terminal. The axon terminal can cause the next neuron to fire, relaying the message.

The axon terminal is at the end of the axon, where the signal is relayed to the next neuron. In SFN, the axon terminal can be damaged or altered, and biopsy shows reduced nerve endings in the skin, possibly due to the damage. The nerve damage causes pain when there shouldn’t be (called mechanical allodynia) and reduced small fiber nerve endings in the skin.[ref]

Genetic research points to a couple of mechanisms for SFN:

Ion channels in the nerve: Genetic mutations in voltage-gated sodium channels are one known cause of small fiber neuropathy. Specifically, mutations in the genes that code for part of the NaV1.7 and NaV1.8 sodium channels have been identified as causing SFN.

This type of sodium channel is located in the small nerve fiber cells that transmit pain signals to the brain (nociceptors). These gain-of-function mutations can cause the sodium channel to not completely close when the channel is turned off, or they can cause the sodium channels to open more easily than usual. Either way, increased nerve firing results.[ref][ref]

Pain receptor: Another cause of SFN shown by genetics research surrounds the TRPV1 channel. TRPV1 is the transient receptor potential vanilloid subtype 1 receptor, activated by heat and capsaicin (spicy chillis). In neurons, activation of TRPV1 signals for pain — like when you eat a jalapeno. A lack of TRPV1 receptors causes ‘thermal analgesia’ or lack of pain from touching (or eating) hot stuff. While this sounds good, paradoxically, a lack of TRPV1 receptors is associated with SFN.

Inflammatory cytokine: Research shows that TNF-alpha, an inflammatory cytokine, is involved in neuropathic pain through the activation of TRPV1 channels along with the TNF-alpha receptor.[ref]

Rare mutations: In addition to the voltage-gated sodium channel mutations known to cause SFN, a 2022 study found that patients with SFN were more likely to have rare mutations that affected the function of other ion channels and other TRP channels.[ref] This means that there are multiple ways that impaired ion channels (including potassium channels) or altered TRP pain receptors can influence susceptibility to small fiber neuropathy – explaining why there is likely no one-size-fits-all solution.

Small Fiber Neuropathy can be part of another disorder:

Looking beyond genetics, small fiber neuropathy can be caused by autoimmune disease. Autoantibodies to neuronal proteins, such as trisulfated heparin disaccharide and fibroblast growth factor, are found in about 20% of patients with SFN.[ref]

Disorders that are associated with small fiber neuropathy include:[ref][ref][ref][ref]

• Hereditary: rare genetic diseases including sodium-channel disorders, Fabry disease, Wilson’s disease, familial amyloidosis, hemochromatosis
• Metabolic: diabetes or insulin resistance.
• Micronutrient deficiency: vitamin B12 deficiency, vitamin B6 deficiency or excess, or copper deficiency
• Infectious and post-infectious: Lyme, HIV, hepatitis C, SARS-CoV-2
• Toxins or medications: alcohol, chemotherapy, vaccine reactions, or neurotoxic drugs
• Autoimmune /inflammatory: lupus, sarcoidosis, rheumatoid arthritis, chronic inflammatory demyelinating polyneuropathy, FGFR3 autoantibodies, primary systemic amyloidosis, fibromyalgia, celiac, monoclonal gammopathy, neuropathic POTS, and Ehlers-Danlos syndrome

About 50% of patients with small-fiber neuropathy get a diagnosis of idiopathic, meaning no known cause.[ref] For some (most?) of these patients, there could be a genetic cause or an underlying genetic susceptibility to the root cause. For someone diagnosed with idiopathic SFN, pursuing the root cause may help with dialing in the right solution or treatment.

Overlapping conditions with SFN:

About 21% of SFN cases have an underlying autoimmune or inflammatory condition.[ref]

Here are some common immune-mediated disorders that overlap with SFN, leading  to missed or delayed diagnoses:

Fibromyalgia:
Between 40-60% of people diagnosed with fibromyalgia meet the biopsy criteria for small fiber neuropathy, according to one study.[ref]

Related article: Fibromyalgia genes

Mast cell activation syndrome (MCAS) or hereditary alpha tryptasemia (HαT):
In a study involving patients with MCAS or HαT, about 80% of each patient group were found to have reduced small nerve fibers consistent with SFN.[ref]

Related article: MCAS genes

Chronic Lyme:
A study in people with widespread pain symptoms after Lyme disease showed that small fiber neuropathy was present in all patients. The patients all responded to IV immunoglobulin therapy.[ref]

Related article: Chronic Lyme disease susceptibility genes

Celiac:
Small fiber neuropathy was found in celiac patients who also had numbness and tingling in the periphery.[ref]

Related article: Celiac genes

Ehlers-Danlos Syndromes:
Small fiber neuropathy is also common in people diagnosed with joint hypermobility syndrome or EDS hypermobility.[ref]

Related article: Ehlers Danlos and hypermobility hEDS genes

Postural orthostatic tachycardia syndrome (POTS):
Neuropathic POTS is a subtype of POTS involving small fiber neuropathy that affects blood vessel function in the legs. While often diagnosed as POTS due to the changes in heart rate upon standing, neuropathic POTS has small fiber neuropathy as the underlying cause. This form of POTS is associated with blood pooling in the legs and Livedo reticularis.[ref]

Related article: Genes related to postural orthostatic tachycardia syndrome (POTS)

Vitamin B12 deficiency:
Skin biopsy samples in people with vitamin B12 deficiency show that “vitamin B12 deficiency causes symptomatic as well as asymptomatic small fiber loss”. [ref] Conditions such as pernicious anemia or long-term lack of dietary B12 could cause or contribute to SFN.[ref]

Related article: Pernicious anemia and genetic causes of B12 deficiency

Small fiber neuropathy in Covid and long Covid:

Several viruses, including HIV, hepatitis C, and now SARS-CoV-2, are associated with an increased relative risk of small fiber neuropathy.

Studies on SFN in Covid show:

• A study involving 23 patients who had recovered from Covid showed that 91% had changes to the cornea consistent with small fiber neuropathy. Nerves in the cornea express ACE2 receptors as well as other receptors that the SARS-CoV-2 virus can use for entry. Alterations in the corneal nerves can cause sensitivity, pain, and dry eyes.[ref]
• The Mayo Clinic published a study in April of 2021 showing that autonomic dysfunction could follow Covid infections. Among other findings, the study showed that COVID-19 exacerbated small fiber neuropathy in people who already had it.[ref]
• Mt. Sinai also published a study showing small fiber neuropathy developing in patients after COVID-19.[ref]
• Another study from Mass General showed new onset of small-fiber neuropathy in patients with long Covid.[ref]

Long Covid may also involve damage to the small fiber neurons.

A follow-up study of people developing neuropathy or sensory changes from Covid showed that skin biopsy results for 82% of the patients still showed SFN long after the infection. Importantly, 70% of the patients also had autonomic dysfunction symptoms.[ref] Another study looked at piloerector muscle nerve fiber density in biopsies from long Covid patients. The results showed “autonomic small fiber damage is a prominent and measurable feature of painful long COVID syndrome”.[ref]

A 2026 study showed that gastric mucosal biopsy samples in long Covid patients had a significant reduction in the autonomic nerve density. The researchers compared biopsy samples from 12 long Covid patients to those of 9 patients who underwent biopsies for dyspepsia. The long COVID patients had significantly reduced nerve density, including cholinergic nerves. This type of nerve is unmyelinated and meets the definition of small fiber nerves, but the small study doesn’t really distinguish the nerve type exactly – so a conclusion of SFN from long Covid can’t fully be drawn here.[ref]

Small Fiber Neuropathy after vaccinations:

A rare side effect of several vaccines includes small fiber neuropathy:

• Case studies show a few cases of SNF onset after the HPV vaccination.[ref][ref]
• An observational study of 23 people with neuropathic symptoms after a Covid vaccine found that >50% of them met the criteria for new-onset SFN (biopsy, symptoms). [ref]
• A case study published in April 2021 outlines the reaction of a 57-year-old woman who developed small fiber neuropathy a week after the Pfizer mRNA vaccine. Antibody testing ruled out a prior Covid infection, and she was not on any medications nor an alcoholic. Her symptoms included burning and tingling in the extremities, loss of pinprick, and cold sensations in her feet. The biopsy confirmed the small fiber neuropathy.[ref]
• An investigation published in April 2021 that looked at immune-mediated disease flares after the COVID-19 vaccines showed that flare-ups affected 78% of the patients with autoimmune diseases. This investigation included autoimmune diseases that cause small fiber neuropathy.[ref]

Reversing small fiber neuropathy:

Nerve fibers can and do regrow, and this can occur after removing the trigger or underlying cause of the nerve damage.[ref] However, this isn’t always straightforward (or quick). While nerve-fiber density can improve, sometimes symptoms don’t immediately reverse. Upregulation or hypersensitivity of pain receptors can take a while to return to normal.[ref]

As we head into the Genotype report section to look at your genetic variants, keep in mind that SFN is a combination of genetic susceptibility and trigger factors.

Lifehacks:

First, some encouragement:
You may read on health websites that small-fiber neuropathy is a lifelong, progressive disease. No hope, essentially. Research studies show that isn’t true — at least not for everyone. Small nerve fibers have the highest regenerative capacity of any nerve, and preventing future damage or reversing some of the current damage may be possible. I want to encourage you to keep looking for solutions and not take ‘it’s a lifelong problem’ as a final answer.[ref]

Test first: The starting point for SFN is to talk with your doctor or neurologist about getting a skin biopsy to test. Your doctor can order the test kits and do it right in the clinic, in most places. While symptoms and even genetic susceptibility can give you a starting point, you can’t really know that you have SFN without testing for it.

Dietary and lifestyle changes:

Metabolic causes:
If your small fiber neuropathy is related to metabolic health (diabetes, pre-diabetes), then focusing on your diet is an obvious place to start. Test your blood glucose levels:

• If you don’t know your normal fasting blood glucose levels, you can get a blood glucose meter at most pharmacies or even large grocery stores. They are relatively inexpensive and will give you a baseline to know if you should focus on your blood glucose levels for SFN.
• If your fasting blood glucose is high, talk with your doctor about your options. Dietary interventions can include cutting out sugar and processed foods, and replacing those foods with a whole-foods diet.

Autoimmune diet:
If you think your small fiber neuropathy is due to an autoimmune disease, look into the Autoimmune Paleo (AIP) diet. It essentially cuts out processed foods and common allergens. The diet focuses on nutrient-dense whole foods. If your SFN is related to celiac disease, then a strict avoidance of gluten may be needed. Talk with your doctor about your best options for autoimmune-related SFN.

Alcohol Avoidance with SCN11A:
Mutations in SCN11A that cause small fiber neuropathy and episodic pain are aggravated by alcohol.[ref] Avoiding alcohol may not help everyone with SFN, but it is worth experimenting to see if alcohol exacerbates your nerve issues.

General dietary goals:
In general, supporting nerve function with a healthy diet is a good idea. This can include whole foods, including omega-3 fatty acids, limiting added sodium and sugar, and meeting your dietary requirements for vitamins and minerals with a well-rounded diet. The overall goal is to reduce inflammation and prevent nutrient deficiencies that could worsen the nerve damage.

Limiting excess sodium:
Several clinical websites recommend limiting sodium or at least making sure you aren’t eating a lot of high-sodium foods with SFN. One reason for the recommendation to limit excess sodium is that the sodium-channel mutations related to SFN cause an increase in function, allowing the nerve to fire too much.[ref]

Potassium in your diet:
Potassium is one mineral to be sure to check to see if you are getting enough of in your diet to support optimal nerve function. While you don’t want to go overboard with potassium supplements (a sudden excess of potassium is bad), making sure that you are getting enough through your diet is important. Foods rich in potassium include potatoes with the skin, bananas, spinach, and avocados. [ref][ref]

Therapies available:

Below are a few of the therapies that are available for SFN with good research or clinical trials on them. There are also a number of therapies undergoing clinical trials right now, so be sure to keep up with ongoing research.

IV immunoglobulins:
A 2018 study showed that IVIg therapy helped about three-quarters of the patients with small fiber neuropathy associated with an autoimmune disease.[ref] Talk with your doctor about whether IV immunoglobulin therapy would be a good option for your situation. IVIg therapy isn’t without possible side effects, and it is costly. Be sure to investigate thoroughly and have an educated conversation with your doctor about how to mitigate side effects and how to navigate insurance reimbursement.

Prescription medications:
Your doctor may also have recommendations for prescription medications. In a small clinical trial, both gabapentin and tramadol were more effective than diphenhydramine for SFN pain. Both helped about 1 out of 4 study participants with the pain.[ref] Do some research on the significant side effects of both of those medications before you talk with your doctor about them so that you can make an educated decision.

Ion channel blocker study for neuropathic POTS:
Talk with your doctor about your medication options. A 2026 clinical trial showed that for neuropathic POTS, the subtype associated with small fiber neuropathy, the patients had a better response to ivabradine, a prescription ion channel blocker.[ref] The point here is not necessarily the specific medication but rather that neuropathic POTS may respond to different medications than other types of POTS.

SCN9A gain-of-function mutations:
Lacosamide, a prescription medication for seizures, is being investigated for people with SFN from SCN9A mutations.[ref] Talk with your neurologist about the pros and cons of lacosamide if you have a confirmed SCN9A rare mutation.

Natural supplements for small fiber neuropathy:

Research studies show that a number of natural supplements can help SFN, and understanding your underlying cause of SFN can help you dial in what is more likely to work for you. The links to the research studies are included below, and you’re encouraged to read the study and talk with your doctor about it.

Specialized Pro-resolving Mediators:
Formed from DHA and EPA (fish oil), specialized pro-resolving mediators are a class of lipids that cells produce to resolve and heal inflammation. Several new research articles point to the vital role of specialized pro-resolving mediators in healing neuropathies.[ref][ref] One article points explicitly to the role of pro-resolving mediators in healing from long Covid.[ref]

Learn all the details about SPMs here: article on pro-resolving mediators.

Agmatine Sulfate:
Known for boosting nitric oxide and marketed as a body-building supplement, agmatine sulfate was found in a clinical trial to reduce SFN pain by 46% on average. All patients in the trial had some pain reduction.[ref]

TRPV1 and vitamin D: 
New research shows that vitamin D may be able to bind to the TRPV1 receptor. Topical application of vitamin D shows promise for neuropathy.[ref] Liquid vitamin D supplements or piercing gel caps with vitamin D in coconut oil could be a workaround to try.

Genetic variants that cause nutrient deficiencies:

Correcting an underlying nutrient deficiency can help to reverse SFN for some. Keep in mind that genetic variants can help you figure out where you are likely to be susceptible to deficiency, but a blood test is the only way to truly know what your level of a vitamin or nutrient is.

Related Articles and Topics:

Elevated Fibrinogen: Risk factor for blood clots

Nattokinase and Lumbrokinase: Natural supplements for clots

Spike Protein, Mast Cells, Histamine, and Heart Rhythms

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