A study from the journal Pain, published in June 2013, reports that almost half of the small group of fibromyalgia patients they tested were found to have damage to nerve fibers in their skin and other evidence of a disease called small-fiber polyneuropathy (SFPN).
Small-fiber polyneuropathy is a type of peripheral neuropathy (nerve pain) that occurs from damage to the small unmyelinated peripheral nerve fibers. Although it is characterized by severe pain attacks that typically begin in the hands and/or feet, some people initially experience a more generalized, whole-body pain.
The pain has been described as stabbing, shooting or burning. SFPN can also result in hyperalgesia (increased sensitivity to pain) or allodynia (experiencing pain from stimulation that is not normally painful). Additionally, patients may have abnormal skin sensations such as tingling or itchiness. For some, the pain is more severe during times of rest or at night.
Study Design and Results
The purpose of the study was to investigate possible connections between fibromyalgia and SFPN. The researchers examined 27 adult patients with fibromyalgia diagnoses and 30 healthy volunteers.
Participants went through a battery of tests used to diagnose SFPN, including assessments of neuropathy based on a physical examination and responses to a questionnaire, skin biopsies to evaluate the number of nerve fibers in their lower legs, and tests of autonomic functions such as heart rate, blood pressure and sweating.
The questionnaires, exam assessments, and skin biopsies all found significant levels of neuropathy in the fibromyalgia patients but not in the control group. Of the 27 fibromyalgia patients, 13 had a marked reduction in nerve fiber density, abnormal autonomic function tests or both, indicating the presence of SFPN.
Participants who met the criteria for SFPN also underwent blood tests for known causes of the disorder. None of them had diabetes, which is a common cause of SFPN. Two were found to have hepatitis C. Interestingly, more than half had evidence of some type of immune system dysfunction.
What Happens Next?
"Until now, there has been no good idea about what causes fibromyalgia, but now we have evidence for some but not all patients. Fibromyalgia is too complex for a 'one size fits all' explanation," says Anne Louise Oaklander, MD, PhD, director of the Nerve Injury Unit in the Massachusetts General Hospital Department of Neurology and corresponding author of the Pain paper. "The next step of independent confirmation of our findings from other laboratories is already happening, and we also need to follow those patients who didn't meet SFPN criteria to see if we can find other causes. Helping any of these people receive definitive diagnoses and better treatment would be a great accomplishment."
This is the third separate study in as many months to make some kind of connection between FM and small nerve fibers. There are still many questions to be answered but I think it's becoming increasingly evident that - at least for a number of FM patients - there is some kind of small-fiber nerve involvement.
While the authors of this study seem to think that SFPN may cause some cases of FM, I can't help but wonder if this might be a chicken and egg situation. Does SFPN trigger fibromyalgia or does fibromyalgia lead to SFPN?
We know that people with other chronic pain conditions (i.e. rheumatoid arthritis, lupus, MS) frequently develop FM, so it's not surprising that people with SFPN (a chronic pain condition) might also develop FM. However, since FM manifests as numerous different types of pain in different people, it also seems plausible that something about the pathophysiology of FM could result in damage to the small-fiber nerves.
Regardless, I think all of these studies are bringing us closer to unraveling the mysteries of fibromyalgia, explaining why we're in pain, and hopefully eventually developing more effective treatments.
Oaklander AL, et al. "Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia." Pain. June 5, 2013.