Small Fiber Neuropathy in Fibromyalgia and CFS

In Some Cases, Nerve Damage May be to Blame

Illustration shows bright, star-like structures that are neurons and their radiating axons.
PASIEKA/Getty Images

Is the pain we feel with fibromyalgia and chronic fatigue syndrome from a type of nerve damage called neuropathy? It's an idea that's been around for several years—after all, our pain is very similar—but is garnering wider support as researchers find more evidence.

Research first presented at the American Academy of Neurology's 2010 annual meeting in Toronto suggests that many of us with these conditions have something called small fiber neuropathy—abnormalities in the small nerve fibers, which are near the surface of your skin and deal with pain and temperature sensation. Both pain and temperature sensitivity are extremely common symptoms of fibromyalgia and chronic fatigue syndrome.

In this study, the researchers took skin biopsies from 30 people who had either fibromyalgia, chronic fatigue syndrome, chronic pain syndrome, or a combination of these illnesses, as well as from a control group. Of the people with the painful conditions, biopsies showed that 13 of them, or 43 percent, had evidence of small fiber neuropathy.

That's a large percentage, certainly, but given the small sample size of just 30 people, it's not conclusive. It is, however, promising enough to lead to larger studies in the future.

Dr. Devanshi Gupta, the lead researcher, says doctors should check for small fiber neuropathy via skin biopsies in patients who have the following symptoms:

  • Sharp, shooting pains
  • Orthostatic hypotension (dizziness upon standing)
  • Autonomic symptoms
  • Skin changes related to interrupted nerve supply
  • Incontinence
  • Sexual dysfunction
  • Other neuropathic symptoms

However, some doctors say that skin biopsies aren't reliable enough alone and should only be used to confirm a diagnosis based on examination and history.

You'll likely recognize several of the symptoms listed above as fibromyalgia and chronic fatigue syndrome symptoms, including the pains, orthostatic hypotension, and autonomic symptoms. The overlap of symptoms can make it harder to diagnose small fiber neuropathy based on symptoms and an exam alone, so the biopsy may be more useful for confirming the diagnosis in us than in the general population.

Further Testing

A small study published in a 2013 issue of brain has provided further evidence of small nerve fiber neuropathy in fibromyalgia.

Researchers examined the small fibers in different areas of the body using three different methods: sensory testing, pain response, and skin biopsy. They compared them between people with fibromyalgia, those with depression, and healthy control subjects.

They determined that people with fibromyalgia had:

  • Impaired small fiber function that lead to increased temperature sensitivity
  • Sensory irregularities in the feet, face, and hands
  • Lower total nerve fibers and fewer regenerating nerve fibers in the skin​
  • Fewer unmyelinated nerve fiber bundles in the skin, but normal levels of myelinated nerve fibers

Researchers concluded that all three testing methods support the idea of impaired small fiber function, and therefore a high likelihood of neuropathic pain, in fibromyalgia.

Understanding the Science

A quick lesson in neurology now, so that these findings make sense to you.

First, look at the picture above. The pink spots are neurons, the cells that make up nerves. The stringy things connecting them are called axons or fibers.

The fibers in the skin, organs, and peripheral nerves are called C fibers or small fibers. Their job is to provide sensation for your skin and to control autonomic function--all the automatic jobs your body does, like regulating heart rate, breathing, and body temperature. Damage to these nerves is called peripheral neuropathy.

Now let's look at the final finding listed above: Fewer unmyelinated nerve fiber bundles in the skin, but normal levels of myelinated nerve fibers.

Picture a large electronic cable cut in half. Inside, it contains a bunch of smaller cables that are bundled together and put inside a casing. Small fibers in your body are bundled in a similar way as they travel together away from nerve cells and toward the areas they serve.

Some of those bundles are in a protective casing called myelin, or a myelin sheath. The medical term for a sheathed bundle is myelinated.

Other bundles are "naked." They don't get a myelin sheath. It's these naked, unmyelinated bundles that, according to this study, appear to be damaged in fibromyalgia. That could be an important clue to researchers as they try to uncover the reasons for the damage.

The Relevance

More evidence is mounting to support the theory that these conditions, or at least a large subgroup of them, are neuropathic. The prevalence of intense nerve pain, strange nerve sensations, and abnormal nerve response all point that direction, as does the fact that many of us are helped by treatments aimed at neuropathy, such as Lyrica (pregabalin) and Neurontin (gabapentin). Checking for small fiber neuropathy may help doctors determine which of us are likely to respond to these kinds of treatments.

This could be an extremely important avenue of research. Doctors understand neuropathic pain. It's common in diabetes and as a result of nerve damage. It's a concrete explanation for our pain, which is currently classified as "poorly understood" or "idiopathic" (meaning without cause.)

It also raises a new question - what is damaging our small fibers? Is it our immune systems, which would mean fibromyalgia is autoimmune? (We already have some evidence suggesting that at least some cases of chronic fatigue syndrome are autoimmune in nature.) Do we lack an enzyme that aids in axon growth and repair? Is it a problem with cellular metabolism (mitochondrial dysfunction)?

Let's hope that researchers start asking those questions and looking for answers, because if it truly is nerve damage--and not just dysfunction--it brings us better credibility along with more concrete targets for treatment.

A Word From Verywell

So if this research is accurate and just under half of us have this type of neuropathy, what does that mean for the rest of us? That's something that'll need to be explored further, but that exploration will be much simpler if they can exclude the subgroup with small fiber neuropathy. We know we're not all alike, and the more we can be accurately subgrouped, the sooner we'll be able to find real answers to our many questions.

Was this page helpful?
Article Sources
  • Gupta D, Harney J. Small fiber neuropathy demonstrated in pain syndromes. Poster session presented at Annual Meeting of the American Academy of Neurology; 2010 Apr 10-17; Toronto, Ontario.
  • Uceyler N, et al. Brain. 2013 Jun;136(Pt 6):1857-67. Small fibre pathology in patients with fibromyalgia syndrome.