Introduction
Fibromyalgia syndrome (FMS) is relatively common, occurring in approximately
2 percent of the general population. Women are more likely to have symptoms of
FMS than men. Ten percent to 30 percent of patients seen in an average
rheumatology practice will have fibromyalgia. The average yearly cost to treat
FMS is approximately $2,000, about the same cost as the treatment of
osteoarthritis.
Definition
All patients with FMS complain of widespread pain. Other very common
symptoms include fatigue, sleep difficulties, and often some depression or
anxiety. Other non-specific symptoms include intermittent constipation and
diarrhea, frequent urination, headaches, numbness and tingling of the arms and
legs, and difficulty concentrating.
The American College of Rheumatology classification criteria for
FMS include the physical finding of tenderness at anatomic areas called tender
points. Eighteen such tender points have been designated. Patients with FMS will
feel tenderness at palpation of at least 11 of these 18 points. Traditional
laboratory tests and X-rays should be normal.
Conditions that might mimic FMS include other muscle diseases
such as polymyositis, endocrine diseases such as hypothyroidism or abnormalities
of calcium metabolism, inflammatory diseases such as polymyalgia rheumatica, and
neurologic conditions such as Parkinsonism. Most of these conditions can be
diagnosed by history and physical examination with minimal laboratory testing.
(Figures to the right: These show common areas of pain and
tenderness (called "tender points") in people who have fibromyalgia.)
The cause of FMS
In the mid 1970s, patients with FMS were studied in a sleep laboratory and
discovered to have brain wave abnormalities during deep sleep. This discovery
resulted in great interest in the pathophysiology of FMS. Currently, a number of
neurohormonal abnormalities — such as elevated substance P in the central
nervous system, low circulating growth hormone, and serotonin and other
abnormalities — have been found. Recent research suggests that patients with
fibromyalgia may have central nervous system dysfunction leading to
amplification of normal pain signals. The precise pathophysiological pathway
remains unproven. Certain clinical relationships, however, provide insight about
the symptoms experienced by patients with FMS. These clinical relationships
include:
- Patients with FMS have lower pain thresholds than the general
population.
- The mechanisms responsible for low pain thresholds are central, not in
the peripheral nerves or muscles.
- Changes in mood and concentration are common.
- FMS is not a discrete disorder. Symptoms of FMS exist as a continuum
throughout the population.
- The number and severity of tender points and the severity of FMS
symptoms are directly related to the degree of distress.