Fibromyalgia may be more common than previously believed, especially among men, according to a new Mayo Clinic study. Researchers there used two different methods to analyze how common the condition is in one Minnesota county. The findings, published in Arthritis Care & Research, offer new insights into a disorder that is difficult to diagnose and treat.

Fibromyalgia causes widespread muscle and joint pain as well as fatigue, sleep problems and cognitive difficulties. Although considered a rheumatic disease, it doesn’t damage the joints or other tissues. Instead, symptoms result from changes in the way the brain and spinal cord process and transmit pain signals.

Until recently, fibromyalgia has been thought to affect women in more cases than men. But experts now say men may be underdiagnosed. Study co-author Daniel Clauw, MD, a professor of medicine in the division of rheumatology and director of the Chronic Pain and Fatigue Research Center at the University of Michigan in Ann Arbor, believes men might account for as many as one-third of undetected fibromyalgia cases. One of the main reasons it’s undetected is because of the way the disorder is diagnosed, says Dr. Clauw, a leading researcher of fibromyalgia pain.

Since 1990, fibromyalgia has been diagnosed using a checklist developed by the American College of Rheumatology (ACR). The checklist has been criticized for omitting key symptoms – such as fatigue, depression, sleep difficulties and cognitive problems – and requiring a difficult-to-perform “tender point” exam – a physical check for 18 predetermined painful areas on the body.  

In 2010, the ACR published a new checklist that includes important symptoms (such as fatigue) previously left out. The checklist was revised in 2011 so fibromyalgia could be diagnosed without a tender-point exam.

For the study, Mayo Clinic researchers used both the 1990 and the 2010 checklists to look for fibromyalgia in the population of Olmsted County, Minn. “It was like using two different lenses with two different powers,” says lead author Ann Vincent, MD, medical director of the Fibromyalgia and Chronic Fatigue Clinic at Mayo Clinic in Rochester, Minn.

First, researchers retrospectively reviewed the medical records of nearly 3,500 patients with possible fibromyalgia. Of these, roughly one-third had been officially diagnosed by a doctor using the 1990 criteria. After taking into account age and sex, researchers determined fibromyalgia affected 1.1 percent of the county’s population.

Researchers then surveyed a random sample of adults in the county using the revised 2010 checklist. Of those who responded, 5.3 percent met the criteria for fibromyalgia. Researchers again accounted for age and sex, and then calculated that fibromyalgia affected 6.4 percent of the county’s population, suggesting that it might be more common than the number of officially diagnosed cases indicates.

Based on the survey, the rate of fibromyalgia in women was three times higher than officially diagnosed; in men it was 20 times higher.

Dr. Vincent says the low percentage of men diagnosed with fibromyalgia using the tender-point criteria makes sense.

“Men are innately less tender than women and they’re less likely to pay attention to pain or seek medical attention for it,” she says. “What this study shows is that men who meet the 2010 criteria for fibromyalgia are unlikely to have been diagnosed [using earlier standards].”

In addition to improving diagnosis, Dr. Vincent says broadening the definition of fibromyalgia to include symptoms other than pain is likely to improve treatment, too.

“Fibromyalgia is multidimensional,” she says. “Patients have pain receptors firing all the time. This generates a lot of pain, to which the body gradually becomes sensitized. And in fighting that pain, people become fatigued, have unrefreshing sleep and cognitive problems. It’s important for primary providers to recognize that chronic pain kicks the symptom burden much higher and that symptom management [is important].”

Dr. Clauw adds, “Some of the same neurotransmitter abnormalities that cause fibromyalgia pain are driving memory and sleep disturbances. [Traditional] pain medications only make pain better, whereas fibromyalgia drugs like Lyrica (pregabalin) and Cymbalta (duloxetine) also make sleep, anxiety, depression and fatigue better.”

Both doctors emphasize that the 2010 guidelines are intended to complement, not replace, the 1990 criteria. Dr. Vincent says, “The most important finding of our study is that the new criteria provide a more comprehensive way for clinicians to recognize fibromyalgia.”

Lesley Arnold, MD, professor of psychiatry and director of the Women’s Health Research Program at the University of Cincinnati College of Medicine in Ohio, agrees.

“The 1990 criteria are still the gold standard for research,” she says. “Combined with the 2010 criteria, they do a very good job of identifying people thought to have fibromyalgia. And the 2010 criteria, by leaving out the tenderness requirement, may allow more men to be identified who may benefit from some of the treatments that are effective for fibromyalgia.”

At the same time, she urges caution in interpreting the prevalence data.

“One of the limitations of the study is the low participation rate in the random survey. Only 27 percent of people responded overall, and those patients are more likely to have symptoms, so [the results] don’t represent actual prevalence,” says Dr. Arnold. “But it does raise the possibility that [fibromyalgia] is more common than originally thought, and certainly more common in men.”