Treatment & Research News

Small Nerve Fiber Damage in Fibromyalgia

The tiny nerves in your skin detect information about pain, temperature, and light touch. Damage to these small fibers occurs in roughly half of fibromyalgia patients and research shows it’s linked to the severity of your pain.

What about your burning, stabbing, prickling, and numbness symptoms? These unpleasant sensations are also produced by the small peripheral nerves and are often associated with neuropathies. Yet fibromyalgia is not like most neuropathic conditions.¹ Indeed, neurologist and lead investigator in the field, Claudia Sommer, M.D., of Germany, describes the findings in fibromyalgia and puts them into perspective.

Loss of Nerve Fibers

Just pressing on your skin or touching a cold object elicits pain. Even brushing your skin can hurt. These symptoms prompted Sommer’s team to examine skin biopsies for changes in the small nerves conveying tactile sensations. They found a reduced nerve fiber density (or number) in patients compared to healthy controls.² In other words, there are fewer fibers because many have been damaged.

But if the sensory fibers in your skin are reduced, shouldn’t this cause less pain, not more? Not necessarily. Sommer offers two explanations for this paradox.

The small fibers in your skin play an important role in filtering out most of the painful stimuli. Otherwise, just sitting for an hour would really hurt. So, a reduction in filtering fibers may lead to more pain transmissions to your brain.

Alternatively, Sommer says, “Many of the skin fibers that are lost may be pleasant touch fibers which can mitigate pain. Unfortunately, we do not have a marker to identify them in the skin biopsies, which could test this hypothesis.”

“My theory is that many fibromyalgia patients have a predisposition (genetic or environmental) to less nerve fibers in the skin,” says Sommer. “It may be one of the susceptibility factors for developing the disease, especially if the lost fibers are those for pleasant touch.”

After Sommer’s initial report, several researchers replicated her findings. In fact, skin biopsies from various locations (feet, thighs, hands, face, and even the eyes) reveal loss of nerve fibers in 40 to 60 percent of fibromyalgia patients.

Taking a Closer Look

Is there something structurally different about the small nerve fibers in the skin of fibromyalgia patients? Sommer’s team used electron microscopy to answer this question.³

“Regardless of whether you take the biopsy at the lower or upper leg, or at the finger, the fiber diameters in fibromyalgia patients are always thinner than normal,” says Sommer. This finding occurs in patients with fiber loss as well as those without it. As a result, Sommer speculates that this thinning of fibers precedes their eventual loss in the skin.

Altered Nerve Function

Putting aside the structural damage, the skin fibers also behave differently. They give off an excessive number of signals even when they are not stimulated. It’s spontaneous activity and can be measured by inserting an electrode needle into the skin.

Why the skin fibers are in a hyperactive state is unclear and the finding applies to fibromyalgia patients with and without nerve fiber loss. “We might not even see the early phases of fiber degeneration, where spontaneous activity might be the strongest,” says Sommer. In fact, she suspects the hyperexcitable fibers precede the structural changes (before they thin out and disappear). However, more research is needed.

Links to Symptom Severity

If you are wondering whether the reduced skin fiber density explains your symptoms of numbness, tingling, and burning or stabbing pain, the answer is NO. These neuropathic-like symptoms occur in fibromyalgia patients regardless of their skin biopsy findings. However, Sommer’s group found symptom severity is worse in patients with widespread reductions in nerve fibers.⁴

Some patients showed the abnormality involving the long nerves ending in their feet and others showed it in their upper thighs (short nerves). But 15 percent had damage to the nerve fibers in both their feet and thighs. In other words, both their long and short nerves were affected. Based on multiple symptom questionnaires, Sommer says, “This subgroup is more severely impacted by their fibromyalgia.”

What About Brain Function?

“My lab is not only looking at the skin, but we are also looking at the brain,” says Sommer. She found decreases in cortical thickness and white matter (the protective sheaths). She also found altered communication between brain regions. These abnormalities are well-documented in fibromyalgia patients. But the question is, can they be linked to the loss of small fibers in the skin? The answer is yes.

All three brain abnormalities were more pronounced in the subgroup of patients with nerve fiber loss.⁵ Summing it up, Sommer says, “More severe small fiber loss in the peripheral nervous system corresponds to a greater severity of central nervous system abnormalities. Rather than an either-or situation, these systems are interacting with each other.”

Sommer’s Fibro Model

“I suspect there is a genetic predisposition and there are also adverse life events,” says Sommer. “This can lead to changes in the immune system and a disruption of substances that regulate nerve growth and survival. There are also lifestyle and environmental factors. And all these processes may damage the nerve fibers in such a way that they develop ongoing activity.”

“If this ongoing activity continuously arrives at your brain, it can disrupt the pain control circuits,” says Sommer. “In turn, this can lead to altered pain processing, which then feeds back to the whole process. It’s a vicious cycle.”

Are Men Different?

A recent study of 43 men documents reduced nerve fiber density compared to healthy male controls.⁶ Looking at the subgroup of men with nerve fiber loss, they also experienced more severe fibromyalgia symptoms.

Possible Treatments

With half of fibromyalgia patients displaying small nerve fiber abnormalities, do neuropathic pain medications work better in this subgroup of patients?

Sommer compared the response to two medications (pregabalin and duloxetine) in patients with and without evidence of skin fiber loss.⁷ She found no relationship between nerve fiber loss and improved drug response. Unfortunately, the number of patients taking either medication was too small to completely rule out an effect.

There is another explanation for the failure of neuropathic pain medications. Fibromyalgia is not like other conditions with small fiber neuropathies. Typically, neuropathies only involve the long nerve fibers (not the short ones). It also does not include thinning of the fibers (decreased diameters), which exist in fibromyalgia patients.

Important Takeaways

The neuropathic-like symptoms of numbness, tingling, burning and stabbing pain occur in fibromyalgia patients regardless of their skin fiber density. Still, those with nerve fiber damage associated with both long and short nerves have more severe symptoms.

Fibromyalgia patients with and without nerve fiber loss appear to have hyperactive nerve fibers and their diameters are smaller. More studies are needed to understand the impact of these changes.

There are no proven treatments for the skin fiber abnormalities in fibromyalgia. Nevertheless, reduced small fiber density is an objective finding in half of patients. It also highlights the role of the peripheral nervous system in this disease.

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References for Small Fiber Nerves in Fibromyalgia

Sommer C, Üçeyler N. Pain Rep 10(1):e1220, 2025. Free Report
Üçeyler N, et al. Brain 136(Pt6):1857-67, 2013. Abstract
Doppler K, et al. Pain 156(11):2319-2325, 2015. Abstract
Evdokimov D, et al. Ann Neurol 86(4):504-516, 2019. Abstract
Aster HC, et al. Sci Rep 12(1):6707, 2022. Free Report
Feulner B, et al. Pain Rep 9(6):e1212, 2024. Free Report
Aster HC, et al. Pain Res Manag 2022:1217717, 2022. Free Report