You may have heard the term “small fiber polyneuropathy” in the past few years in some of the newer, cutting edge discussions of chronic pelvic pain, central sensitization and chronic overlapping pain conditions. Research studies are now showing that a significant number of pelvic pain patients have observable neuropathies in some of the smallest nerves in their skin and organs. A pivotal 2018 study found that 64% of patients (men and women) with chronic pelvic pain and/or multiple pain conditions (IC, IBS, fibro, etc.) tested positive for SFPN.1 This was confirmed through two small biopsies taken from the skin in the lower leg.

Think about this for a moment. A tangible, objective analysis of a small piece of skin could confirm nerve abnormalities and explain why a patient may be struggling with pain. This could revolutionize diagnostic methods and, more importantly, provide proof that a patient has a nerve dysfunction. Need evidence for a disability application? These biopsy results could speak volumes about why some are suffering from IC, IBS and other painful conditions. Better yet, this data will absolutely destroy anyone who suggests that the pain is “all in your head.” No, it could be in how the small fibers in the nervous system are functioning.

To understand small fiber neuropathy, you have to go back to the roots of our nervous system. The central nervous system is made up of the brain and spinal cord. Within the CNS, you will find the somatic nervous system, which manages per- ceptions from your skin and muscle. The visceral nervous system manages major functions in the human body, such as your ability to breathe, blood pressure, bladder and bowel function. There is a separate nervous system that auto- matically manages your GI tract.

Small fibers are nerves that have the smallest diameter. They are found in abundance in your skin, where they relay information about pain and temperature to your central nervous system. When they are damaged or malfunctioning, patients experience heightened pain sensation. Small fibers are also found in the bladder, bowel and blood vessels where they, too, become more sensitive. Patients may feel pain when small amounts of urine are present in the bladder which we often call a “false sense of fullness.”

Potential Causes of SFN

A neuropathy occurs when a nerve isn’t functioning normally. In some cases, patients sustain an injury to the nerves while, in others, a disease can cause nerves to be damaged. Metabolic causes include diabetes and untreated thyroid dysfunction. Autoimmune diseases, such as Sjogren’s SLE, rheumatoid arthritis, IBD and sarcoidosis can cause neu- ropathy.

A healthy nervous system requires a healthy diet. Patients who struggle with B12 or copper deficiency may notice more neurological driven symptoms. B6, B1 and E can also play a role. If taken in excess, B6 can cause nerve damage which is why patients should never exceed normal dosages.

Some chemicals are quite toxic to the nervous system, including: chemotherapeutics, platinum, taxans, bortezomib and vinca alkaloids. Antibiotics commonly prescribed for patients with bladder symptoms can also cause nerve damage, including: nitrofurantoin, fluoroquinolones and TMP-SMX. Medications for HIV and gout can be harmful, as well as alcohol and exposure to heavy metals.

Some viral infections can damage the small fibers, most notably Lyme disease, herpes simplex, chickenpox, shingles and HIV. Some patients may inherit specific sodium channel mutations or perhaps vitamin B12 processing disorders.

Not surprisingly, the cause may not be found in 30 to 50% of patients.

Symptoms of SFN

The symptoms small fiber neuropathy in the skin are “sensation” or sensory disturbances, including: cold-like pain, tingling, pins and needles, burning pain, electric pain, allodynia and hypersensitivity of the skin. You might feel like some sand is in your shoe or a pebble in your sock. Symptoms usually worsen at night or during periods of rest and can fluctuate daily.

The symptoms of small fiber neuropathy in the autonomic nerves include: dysautonomia, dry eyes, dry mouth, dry skin, dizziness, light- headedness when standing, GI dysmotility, neurogenic bladder, erectile dysfunction and abnormal sweating.

Diagnosis

A diagnosis is made by a neurologist who will study your symptoms, perform a physical examination and then take a small skin biopsy (just 3 mm) on the lower leg above the ankle. They may also perform a tilt-table test.

Blood testing is essential to rule out B12 or copper deficiencies, as well as any toxicities present, such as heavy metals, industrial toxins and organophosphate insecticides. People who work with chemicals, welding or mining may be required to do a 24 hour urine test that may reveal arsenic, lead, mercury or cadmium toxicity. They will screen for hepatitis, diabetes, various inflammatory conditions, lyme disease, celiac disease, etc. etc.

They should also conduct a thorough review of medications that have been used, including: therapy for cancer or HIV, statins, colchicine, isoniazid, dapsone, hydralazine, lithium, phenytoin, vitamin B6, disulfiram, amiodarone, procainamide, perhexiline, streptokinase, nitrous oxide, metronidazole, nitrofurantoin, gold, thalidomide, TNF-antagonists, antibiotics (chlramphenicol, fluoroquinolones, metronidazole, nitrofurantoin).

Treatment

It is vitally important to stop any ongoing damage to allow the nerve fibers to regenerate. If a B12 deficiency is found, it should be treated immediately.

Neuropathic pain is treated in five potential ways:

  1. Antidepressant medications (Duloxetine, Venlafaxine, amitryptiline, nortryptiline) to calm the nervous system.
  2. Antiepileptic medications (gabapentine, pregabaline, carbamazepine, etc.)
  3. Opiate medications
  4. Topical medications (lidocaine, capsaicin)… particularly compounded formulations of lidocaine, gabapentin, amitryptiline, ketamine and baclofen.
  5. Neuromodulation and Transcranial Magentic Stimulation (TMS)

Some patients may require the use of immunodulatory agents, such as IVIG.

Conclusion

I have no doubt that I have small fiber polyneuropathy. I feel symptoms as I’m trying to fall asleep when I feel random unprovoked but mild sensations of pain or pin pricking on my skin. It’s usually one small spot somewhere on a lower leg, upper leg, back or hands. I keep two big tubs of Cerave on my nightstand that I use immediately, especially CeraVe Itch Relief Moisturizing Cream. This is also my cue to remember to take Vitamin B12 and D, which I have been remarkably low in over the years.

In addition to the normal host of IC symptoms over the years, I’ve had dry eyes and dry mouth for decades as well as hypothyroidism. I am very sensitive to caffeine, which causes tachycardia, PVC’s and/or arrhythmias. I also have delayed stomach emptying, aka gastroparesis. I don’t have the lightheadedness or sweating issues.

My sister, my mother, my brother and grandmother all had or have very sensitive skin. Could we have inherited a Vitamin B12 processing disorder, as some researchers are currently exploring (aka porphyria)? Or could this be the result of exposure to various chemicals or antibiotics? I simply don’t know. But, with this information, I certainly am going to be much more cautious about taking medications that can trigger nerve damage and reducing/removing toxic chemicals in my home and environment.

The most important take home point from this article is that we now have an objective method of verifying nerve dysfunction, a simple skin biopsy. Countless IC, IBS, chronic prostatitis, fibromyalgia, CFS, vulvodynia patients have been denied disability coverage for the lack of objective data. This is groundbreaking.

If you are struggling with nerve sensitivity, especially sensitive skin, please talk with your doctor. It’s important to have a diagnostic workup, especially some basic blood work, to determine if you, too, might have a B12 deficiency or something else going on. If the symptoms persist, referral to a neurologist for a biopsy and further workup is recom- mended.

References

1. Chen A, et al. Small Fiber Polyneuropathy Is Prevalent in Patients Experiencing Complex Chronic Pelvic Pain. Pain Medicine 2018; 0:1-7