Many Fibromyalgia Patients Have Small-Fiber Polyneuropathy

The underlying cause(s) of fibromyalgia is still undetermined but a recent study found that almost half of all fibromyalgia patients had small-fiber polyneuropathy, a potentially treatable disease that could be traced back to diabetes, malignancy, or other cause of nerve damage. The lack of a distinct pathology associated with fibromyalgia means that it is technically a syndrome rather than a disease.

This also means that many patients are trapped in a cycle of failed therapies and no clear curative treatment for the widespread chronic pain condition that can cause neck pain, shoulder pain, fatigue, and cognitive symptoms.

This research may provide an opportunity for specific testing and tailored treatment that can make a huge difference to quality of life for fibromyalgia sufferers.

A Target for Fibro Treatment?

This latest fibromyalgia research was carried out at Massachusetts General Hospital by Anne Louise Oaklander, MD, PhD, and colleagues from Harvard Medical School in Boston. Details of the work were presented late last month at the American Neurological Association (ANA) 137th Annual Meeting and Oaklander hopes that small-fiber polyneuropathy (SFPN) could represent a target for effective treatment for many patients.

SFPN and Fibromyalgia – Similarities and Differences

Fibromyalgia differs from SFPN in that the latter is a true disease with objective tests for diagnosis and the possibility of disease-modifying treatments. However, the symptoms of fibromyalgia and SFPN are very similar with widespread chronic pain, including neck pain, and tender points found in both conditions.

Skin Punch Biopsies and Other SFPN Tests

During this latest research, the scientists looked at twenty-five patients meeting the criteria for clinical diagnosis with fibromyalgia. These patients were all over eighteen years old (mean age was 46.5) and they were demographically matched with controls (average 44.8 years old). Just as the majority of those diagnosed with fibromyalgia are women, so it was in this study that 76-79% of patients and controls were women. All patients were tested for SFPN using standard diagnostics autonomic function testing, an early neuropathic scale, and PGP9.5 immunohistochemical staining of a 3mm skin punch biopsy specimen.

Nerve Loss in Fibromyalgia Patients

As nerve fiber density differs between men and women and young and old, the tests and markers were normalized and analyzed in a blinded fashion to remove bias. Small-fiber polyneuropathy is diagnosed when a patient’s nerve fiber density is below the fifth percentile for their predicted value, given their age and sex. Half of the fibromyalgia patients showed evidence of nerve loss, with 46% meeting strict criteria for SFPN (17% of controls also met these criteria). Using just the IENF staining testing method, some 40% of the fibromyalgia patients met SFPN criteria but there was no overall difference between fibromyalgia patients and controls on autonomic function testing (17% of the former met SFPN criteria, versus 15% of controls).

Diabetes and Fibromyalgia – What’s the Connection?

These results will hopefully go some way towards helping physicians apply appropriate testing to patients they suspect have SFPN. IENF densities were 28% (plus or minus 6%) of the predicted norm for fibromyalgia patients, whereas they were 47% (plus or minus 6%) for controls. Diabetes is the most common cause of loss of nerve fiber density and small-fiber polyneuropathy in people in the US and many remain unaware that they have diabetes or prediabetes. Uncovering a possible cause of pain in those diagnosed with fibromyalgia could lead to further testing to determine if diabetes, prediabetes or some other condition is at the root of nerve pain. Thus, restoring healthy blood sugar control may, theoretically, reduce symptoms of fibromyalgia in some patients.

Misdiagnosing Neck Pain and Fibromyalgia

There is a real concern that patients with neck pain attributable to no clear cause are given a diagnosis of fibromyalgia and then struggle to undergo further testing to elucidate the cause of their suffering. Decades of pain can cost patients the opportunities for happy and fulfilling careers, relationships and family life, but understanding the real cause of fibromyalgia may change all that.

Treatable Causes of SFPN

Autoimmune conditions, tumors, neurotoxins, genetic mutations, and other causes of SFPN could all be treated and symptoms of pain associated with fibromyalgia may dissipate with such therapy. SFPN can also affect blood pressure homeostasis, gastrointestinal function and other systems not normally connected with simple pain in the neck or chronic pain from fibromyalgia. The often confusing medical and symptom history of patients finally diagnosed with fibromyalgia may incorporate dizzy spells, digestion problems, cognitive symptoms, weakness, numbness and paraesthesia in the limbs, and fatigue, stress and depression.

Testing Fibro Patients for SFPN

SFPN may account for many of these symptoms but, as patients with suspected fibromyalgia are usually sent to a rheumatologist rather than a neurologist such a diagnosis is unlikely to be foremost in the physician’s mind. That this recent study found half of fibromyalgia patients had small-fiber polyneuropathy may change diagnostic procedures for patients presenting with neck pain and other symptoms of fibromyalgia.

Reference

American Neurological Association (ANA) 137th Annual Meeting in partnership with the Association of British Neurologists. Abstract W1409. Poster presented October 7-9, 2012.