Chronic Pain

Recent Findings Related to Fibromyalgia

Small nerve dysfunction in persons with fibromyalgia

Posted Jul 31, 2013

Fibromyalgia is a syndrome that is frustrating to both patients and physicians. Symptoms include chronic widespread pain and muscle tenderness often accompanied by fatigue, problems with sleep, and mood disturbance. Patients with clinical depression also may develop widespread pain during depressive episodes. Some clinicians believe that the symptoms of fibromyalgia are a manifestation of clinical depression or another psychiatric illness, while others believe that fibromyalgia is its own illness that often is accompanied by depression. 

Nurcan Uceyler and colleagues recently published a paper in the journal Brain that provides support for the view that fibromyalgia is a disorder involving specific types of nerve fibers that convey pain sensations to the brain. This group’s research demonstrates specific and objective abnormalities in small nerve cells in this disorder. They also provide data suggesting that the “fibromyalgia syndrome is not a variant of depression but rather represents an independent entity that may be associated with depressive symptoms.”  If replicated, these are potentially important findings that open the door to understanding how this complex syndrome arises.

A variety of nerve cells form fibers that convey information from various parts of our bodies (including muscles, skin, and internal organs) to our brains. Some of these nerve fibers send messages to the brain quickly because they are encased in a layer called myelin that acts as an electrical insulator to enhance the flow of signals. Other nerve fibers are thin and are not wrapped by myelin; messages over these fibers travel more slowly.

Uceyler’s group demonstrated that persons with fibromyalgia have fewer of the small unmyelinated nerve fibers than healthy individuals. Furthermore, patients with fibromyalgia also had a decreased number of these small unmyelinated fibers compared to patients with clinical depression. There were no significant differences between the depressed (pain free) persons and the healthy individuals. The number of larger myelinated nerve fibers was not altered in patients with fibromyalgia suggesting that abnormalities in fibromyalgia specifically involve small, unmyelinated nerve fibers.

These investigators also examined the physiologic functioning of small, unmyelinated fibers by studying electrical activity in the brain when pinprick-type pain was evoked in the skin. The size of the electrical responses in the brain (called pain-related evoked potentials) was markedly smaller in persons with fibromyalgia. Since small, unmyelinated nerve fibers are responsible for conveying this type of pain information from the body to the brain, this decreased response in the brain to pinprick is consistent with patients with fibromyalgia having fewer of these fibers. The authors of the article speculate as to how these abnormalities in small nerve fibers lead to increased pain sensations, but more research will be required to define the exact mechanisms.

For clinicians, distinguishing fibromyalgia from other pain states or from psychiatric conditions including depression remains difficult. Also, prescribing the most appropriate treatments can be challenging. In another recent paper in the Journal of Clinical Rheumatology, Jacob Painter and Leslie Crofford reviewed medications used to treat fibromyalgia. Interestingly, an older antidepressant called amitriptyline has been shown to be beneficial. Amitriptyline can also be helpful in preventing or ameliorating a variety of other pain-related disorders, including migraine headaches and diabetic neuropathy. Certain other antidepressants as well as other categories of medications have also been shown to help patients with fibromyalgia. These authors review data demonstrating that opiate medications are ineffective for the pain of fibromyalgia, and they strongly discourage their use. This is a critical point because other data highlight a significant role for overuse and inappropriate use of opiates for pain in a recent national upswing in opiate abuse, dependence, and serious side effects, including death. In addition to medications, a variety of non-pharmacologic treatment approaches can help patients with fibromyalgia. Education, cognitive behavioral therapy, biofeedback, and gentle exercise may all be somewhat beneficial. Unfortunately, however, this syndrome remains difficult to treat.

In summary, fibromyalgia is a disorder that leads to marked distress as a result of both physical and mental discomfort. Thus, it resides at the intersection of internal medicine, neurology, and psychiatry. Hopefully, research advances will continue to shed light on this poorly understood disorder and will lead to safer and more effective treatments. 

This column was written by Eugene Rubin MD, PhD and Charles Zorumski MD