The government’s division of epidemiology is based in Atlanta at the Centers for Disease Control and Prevention (CDC).

This is not a small department; they have about ten times the budget of the FDA and are kept busy investigating any sudden outbreak of disease around the country, from a common food poisoning to a rare anthrax death. Well, enough about history, now about Fibromyalgia Syndrome (FMS).

Prevalence is a measure of how many people in a population suffer from a disease at one time.  The first general population survey of primary fibromyalgia was reported in the Scandinavian Journal of Rheumatology in 1989 showing a prevalence of 1%. This was just about the same number that was found for people suffering from rheumatoid arthritis. Other surveys of the general population in subsequent years found a prevalence of 0.5% to 5%. A mailed survey of 3006 adults in Wichita, Kansas in 1995, conducted by one of the best known researchers in FMS, Dr. Frederick Wolfe, found an overall prevalence of 2%; 3.4% in females and 0.5% in males.

A 1999 similar general population survey of 3395 individuals in London, Ontario, Canada found an overall prevalence of 3.3%; 4.9% in females and 1.6% in males. This survey found a peak prevalence, meaning the most people in a particular age group (epidemiologists like to categorize people in groups of 10 year age groups), in females of approximately 10% in the 55 to 66 age group.

Both surveys found that FMS, at that time, was associated with low household income and the failure to complete high school. Epidemiologists also like to look for factors that seem to be common among people with a particular disease.

Many people feel that FMS is a disease of the wealthier countries, that it affects people who are better off financially, at least in terms of the world’s population. They do not think FMS extends into other less fortunate countries or the developing nations. Contrary to what has been thought regarding this misconception, FMS was found in 2.6%, 3.2%, and 0.1% of the rural, poor urban, and affluent adult populations, respectively, in north Pakistan. FMS is a world-wide disease.

Surveys made at rheumatology clinics from the 1970s and 1980s indicated that patients with “fibrositis” accounted for approximately 2% to 15.7% of outpatient rheumatology practices. In 1983, Dr. Wolfe found 3.7% of 1,473 new patients in an outpatient rheumatology clinic fulfilled the criteria for “primary fibrositis” and 12.2% of patients with rheumatoid arthritis and 15.7% of patients with primary neck and back pain syndromes met the criteria for “secondary fibrositis.” These studies were done before FMS was recognized by the American College of Rheumatology in 1990; fibromyalgia was then known as fibrositis. The term “secondary” means that the diseases of rheumatoid arthritis and the neck and back complaints were thought to be causing more of these patients’ problems than the problems caused by the “fibrositis.”

An Australian general rheumatology clinic diagnosed FMS in 10.2% of 216 consecutive new referrals in 1992. This was a similar finding to the 10.4% of FMS diagnoses made in 673 patients seen as new consultations to a hospital rheumatology outpatient clinic in Madrid, Spain, two years earlier. In 1995, a random mail survey of Canadian rheumatologists found FMS to be one of the three most common diagnoses made among the new patients they were seeing and was considered by 69% of those physicians surveyed to have increased in frequency within the previous five years.

In the general population surveys approximately 75% of those diagnosed with FMS were female while in the specialty rheumatology clinics the number was slightly higher at 84% to 86%. Women do tend to seek medical care more frequently than males so there is an accepted fact of FMS being under-diagnosed in males.

Epidemiologists are always looking for explanations, for example, why do family practice clinics report an incidence of approximately 2% while major centers such as hospitals may have an incidence of greater than 7%? One reason is something called “diagnosis bias” in which particular physicians may be more prone to recognize and diagnose FMS. For example, rheumatologists and more recent graduates from medical school are more likely to diagnose FMS while orthopedic surgeons are less likely to do so. Has anyone reading this had a similar experience?

So, you may be asking what are the final numbers and statistics? If you were having lunch with a group of FMS epidemiologists, here is what their conversation may sound like:

• According to the CDC, the prevalence of fibromyalgia is about 5%,  with about 5 million adults are affected, as of 2005. However the National Women’s Health Center calculates up to 8 million people are affected.
• The female to male ratio is 7 to 1, so seven times as many females are affected as males.
• Overall the prevalence of FMS increases with age; 1% in women age 18 – 29 and 7% in women 70 – 79 years of age and most women are diagnosed in middle age.
• Most people with FMS have about 3 hospitalizations per year. They also receive about 1.8 million physician visits and 266,00 emergency room visits.

Of more recent concern is the prevalence of FMS in Gulf War veterans, 17% of returning veterans were diagnosed with FMS in one 1998 report. A recent 2010 study describes a chronic musculoskeletal pain syndrome in veterans where those afflicted, similar to FMS patients, reported some of the same symptoms as patients with FMS, in fact, the only major difference was that these occurred in men, which is not unexpected given that they were soldiers. They were tested in a manner that had been used to test patients with FMS by being asked to exercise and then report how they felt. They were then given a “heat stimulus” at different times during their exercise program which was gradually increased and were asked to tell the researchers when it became uncomfortable.

The researchers found that the naturally occurring, exercised induced, muscle pain in these men was said to be more intense than normal, compared to the people they were being tested against; and these people were soldiers! They were also much more sensitive to a heat source the researchers were using to test their responses to an artificial stressor.

This “heat test” is actually something very unique.  It reflects a phenomenon termed exercised-induced hypoalgesia, or EIH.  In people without FMS, exercising tends to make someone able to tolerate a little more discomfort. It happens naturally and involves rather complex processes in the way the nervous system works. Basically, the central nervous system sends messages down the spinal cord to tell the body, “It’s OK, we know you’re hurting a little, and we’re going to deal with it, so let’s not bother with this bit of pain, after all you just finished exercising.” Technically, it’s called “descending inhibition,” where the inhibition refers to inhibition of the sensation of pain. We’ll talk more about this in a later short report on this web site.

In this experimental situation, the soldiers should have been able to tolerate more heat before saying it was uncomfortable due to their exercising. However, the soldiers, like patients with FMS, actually became more sensitive to the discomfort of the heat. Patients with FMS do not have EIH, in fact they have the opposite situation, they become more sensitive as a result of exercise. It has been shown to be one of the characteristic findings of FMS.

Unfortunately, the prevalence numbers for FMS may be changing quite drastically as a result of the war in the Middle East and not in a good way, and there may be far more men joining the ranks of those with FMS.