Is Fibromyalgia Also A Peripheral Neuropathy?

Today's post from neurologyadvisor.com (see link below) looks at a problem that bothers lots of people with or without confirmed nerve damage and that is: is this fibromyalgia: if so, is that a form of neuropathy and if not why not - it seems so clearly to be nerve related? Doctors and scientists now seem to be concluding that small fibre polyneuropathy causes many cases of fibromyalgia...but not all! The article is somewhat complex unless you have a very good understanding of medical terms but you will get the gist of what's being said. Nevertheless, the jury still seems to be out on this question - not that many fibromyalgia and/or neuropathy patients will care - their pain is still excruciating!

Fibromyalgia: A Peripheral Pain Disorder?

Chris Illiades, MD November 13, 2015

 Fibromyalgia is a common, debilitating condition that has long confounded researchers — the syndrome has had no demonstrable pathology or definitive diagnostic test. Now, new research suggests that fibromyalgia may have a neuropathic basis in some patients.

In a study published in the October issue of Seminars in Arthritis and Rheumatism, researchers found that women with fibromyalgia exhibited corneal nerve atrophy consistent with neuropathic pain. The findings suggest that some patients with fibromyalgia may actually have small fiber polyneuropathy (SFPN), a disease with potentially treatable causes.

For the study, noninvasive corneal confocal bio-microscopy was used to examine corneal small fiber nerves in 17 women with severe fibromyalgia and 17 age-matched healthy women. Fibromyalgia patients had a mean Fibromyalgia Impact Questionnaire (FIQ) score of 69.3

CLINICAL CHART: Neuropathic Pain Treatments

Compared with healthy controls, patients with fibromyalgia had significantly thinner corneal stromal nerves (mean, 5.0 ± 1.0 µm vs 6.1 ± 1.3 µm, P = .01), as well as diminished sub-basal plexus nerve density per square millimeter (85 ± 29 vs 107 ± 26, P = .02).3

All but 1 patient in the fibromyalgia group had a Leeds assessment of neuropathic symptoms and signs (LANSS) score above the 12 cut off point, suggesting a neuropathic component to their pain. Patients also had high Composite Autonomic Symptoms and Signs (COMPASS) tallies (54.6 ± 16.9), reflecting prominent autonomic nervous system dysfunction.

Further analysis revealed a link between nerve slenderness and LANSS neuropathic pain symptoms questionnaire scores (Fisher׳s exact test P = .007); similarly, an association was found between sub-basal nerve scarcity and LANSS score (Fisher׳s exact test P = .008).

“We found an association between stromal nerve slenderness and neuropathic pain symptoms,” lead author Manuel Martinez-Lavin, MD, a professor of rheumatology at the Instituto Nacional de Cardiologia Ignacio Chavez in Mexico City, Mexico, told Clinical Pain Advisor.

Although symptoms of neuropathic pain are not uncommon in fibromyalgia, the syndrome has been primarily considered to be a central nervous system (CNS) processing disorder.3,4

“Our group suspects that fibromyalgia is a neuropathic pain syndrome. We believe it is primarily a peripheral nerve disorder that causes central nervous system sensitization. We think that fibromyalgia is sympathetically maintained based on stress as a triggering event; heart rate studies suggest ongoing sympathetic hyperactivity,” Dr. Martinez-Lavin stated, noting that further studies are needed to confirm the controversial hypothesis.

Up To 50% of Fibromyalgia Cases Affected

“I would not say that small fiber polyneuropathy causes all cases of fibromyalgia. However, we now have enough confirmation from independent groups, using different research techniques, to say that SFPN is found in close to 50% of people with fibromyalgia,” Anne Louise Oaklander, MD, PhD, from Harvard Medical School in Boston, told Clinical Pain Advisor.

In a study conducted at Massachusetts General Hospital5, Dr. Oaklander and colleagues used leg skin biopsies to show that 41% of 27 patients with fibromyalgia had undiagnosed SFPN.

In contrast with the nebulous syndrome known as fibromyalgia, SFPN is a disease associated with objective evidence of pathology and pathophysiology that can be included in a differential diagnosis, Dr. Oaklander pointed out.
SFPN Linked To Other Fibromyalgia Symptoms

Although some fibromyalgia patients have symptoms of neuropathic pain, others report widespread pain, deep tenderness, insomnia, cognitive dysfunction, and fatigue.2

Research is clarifying that SFPN causes more symptoms than first thought. Abnormal small-fiber control of muscle microcirculation appears to cause deep tenderness and exercise intolerance4, while poor perfusion of the brain from neurogenic orthostatic hypotension can produce cognitive dysfunction or fibromyalgia “brain fog,” Dr. Oaklander said.

Fibromyalgia often begins after a period of physical or emotional stress. “We propose that stress causes sympathetic sprouting in dorsal root ganglions leading to changes in sodium channel gate keeping. A sodium channelopathy may be the underlying mechanism for some cases of fibromyalgia and small fiber neuropathy,” Dr. Martinez-Lavin explained.
Clinical Implications

“The major clinical implication [of the findings] is that fibromyalgia is real,” Dr. Martinez-Lavin said.

As corneal confocal microscopy is not readily available, ankle skin biopsy remains the recommended method of diagnosing SFPN. Samples taken during an office visit can be mailed to an accredited lab for testing.

“If skin biopsy reveals small fiber polyneuropathy, medical causes should be looked for because disease-modifying treatments, and even cures, may be available,” Dr. Oaklander advised, noting that symptoms may improve with management of underlying conditions, such as autoimmune disease, hepatitis, malignancy, diabetes, or prediabetes.

For patients with fibromyalgia and diagnosed SFPN, medications such as serotonin norepinephrine reuptake inhibitors (SNRIs), tricyclics, gabapentin, pregabalin, and duloxetine may be effective.1,

“If sodium channelopathy can be confirmed as a cause of fibromyalgia, new, more specific sodium channel blockers may be developed to treat fibromyalgia,” Dr. Martinez-Lavin said.

Although the role of small fiber neuropathy in fibromyalgia is still not entirely clear, researchers are now beginning to unravel details about this complex condition. A demonstrable pathology has been found in about half of patients, and a cause is being actively pursued for the other half. Once causes are identified, better treatments often follow — all of which mean a brighter future for fibromyalgia patients.

References
Bottom Line/Health. Fibromyalgia: New Research Helps Unravel the Mystery. http://bottomlinehealth.com/fibromyalgia-new-research-helps-unravel-the-mystery/
Pain Research Forum, Multiple Studies, One Conclusion: Some Fibromyalgia Patients Show Peripheral Nerve Pathologies, http://www.painresearchforum.org/news/33529-multiple-studies-one-conclusion-some-fibromyalgia-patients-show-peripheral-nerve
Ramirez M, Martinez-Martinez LA, Hernandez-Quintela E, et al. Seminars in Arthritis and Rheumatism, Small fiber neuropathy in women with fibromyalgia. An in vivo assessment using corneal confocal bio-microscopy. Semin Arthritis Rheum. 2015. Oct;45(2):214-9. doi:10.1016/j.semarthrit.2015.03.003.
Albrecht PJ, Hou Q, Argoff CE, Storey JR, Wymer JP, Rice FL. Excessive peptidergic sensory innervation of cutaneous arteriole-venule shunts (AVS) in the palmar glabrous skin of fibromyalgia patients: implications for widespread deep tissue pain and fatigue. Pain Med. 2013. Jun;14(6):895-915. doi:10.1111/pme.12139.
Oaklander AL, Herzog ZD, Downs HM, Klein MM. Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia. Pain. 2013. Nov;154(11):2310-6. doi:10.1016/j.pain.2013.06.001.

This article originally appeared on Clinical Pain Advisor.

http://www.neurologyadvisor.com/pain/fibromyalgia-neuropathic-pain-peripheral-nerve-disorder/article/453804/