Fibromyalgia should be considered a condition that exists across a continuum in the population, and is not a categorical disorder as it has often been considered, researchers concluded from a survey analysis in Germany.
On a polysymptomatic distress scale, patients with fibromyalgia had mean scores of 16.4 out of 27, compared with mean scores of 3 in the general German population, according to Frederick Wolfe, MD, of the National Data Bank for Rheumatic Diseases in Wichita, Kan., and colleagues.
With the cutoff diagnostic score being 12 on that scale, 2.1% of the population met the criteria for fibromyalgia, but continuous and linear correlations were seen throughout the population sample for multiple relevant disease domains including pain, physical and psychological distress, and quality of life (P<0.001 for all), the researchers reported online in Arthritis Care & Research.
"We found strong evidence that fibromyalgia is not a discrete -- yes or no -- disorder. Rather, the symptoms that characterize fibromyalgia exist in a continuum from none to very severe across all people in the population," lead author Wolfe told MedPage Today.
"In those with fibromyalgia there is overwhelming polysymptomatic distress, with severe pain and severe symptoms of all sorts," Wolfe explained.
"One doesn't either have fibromyalgia or not have it," he added.
The publication in 2010 of revised diagnostic criteria for fibromyalgia, eliminating the requirement for tender points and emphasizing the importance of a wide variety of symptoms, made population-based studies of the condition more feasible.
Accordingly, Wolfe and colleagues identified a representative sample of 2,445 German adults who completed questionnaires on health, diet, education, and sociodemographics.
"The most important finding of the study is the idea that fibromyalgia is more of a dimensional disorder than a disease," said Brian Walitt, MD, of Georgetown University in Washington, who was not involved in the study.
"That's a very big departure from how people like to think about fibromyalgia," Walitt told MedPage Today.
Fibromyalgia was assessed on the summary polysymptomatic distress scale, as well as on the scale's individual components of the widespread pain index and the symptom severity score as established in the 2010 criteria.
Those revised criteria required patients to have a score of 7 or higher on the widespread pain index and a symptom severity score of 5 or higher, or a pain index score between 3 and 6 and a symptom severity score of 9 or higher. Either variation led to polysymptomatic distress scores of 12 or higher.
The researchers found that the prevalence of fibromyalgia increased significantly with age, being 0.8% in adults younger than 40, rising to 2.5% for those between 40 and 60 and then to 3% for those older than 60 (P=0.004).
The summary polysymptomatic distress score rose by 0.59 units for each decade of life, while the symptom severity score increased by 0.14 units and the widespread pain index rose by 0.45 units.
The widespread belief that women are more commonly afflicted was not borne out, since the prevalence was similar in women and men, at 2.4% and 1.8%, respectively (P=0.372).
In clinical practice before the revised diagnostic criteria were implemented, up to 90% of patients with fibromyalgia have been women, which may have related to their greater likelihood for having tender points and possibly for seeking medical care for these concerns, the researchers observed.
The analysis also identified a strong correlation (r=0.790) between polysymptomatic distress scores and scores on a somatic symptom questionnaire that reflects how severely a person is distressed by symptoms such as fatigue, unrefreshing sleep, and gastric discomfort.
This was shown by the finding that for a diagnosis of fibromyalgia, the area under the receiver operating curve for the polysymptomatic distress score was 0.996 and was similar, at 0.973, for the somatic symptom score, according to the researchers.
Overall, 53.8% of individuals with fibromyalgia had one or more severe somatic symptoms, while 32.7% had two or more, and 38.5% would qualify as having a physical symptom disorder in the proposed DSM-V.
While the prevalence of fibromyalgia in Germany was only about 2%, estimates from the U.S. have been slightly higher, at about 4%.
It's unclear whether this reflects a difference in the populations or more refined measuring techniques, Walitt pointed out.
"Although fibromyalgia in clinical practice is treated as a categorical disorder, the confirmation of fibromyalgia as a spectrum disorder has important research, clinical, and societal connotations," the researchers wrote.
"Future research, whether clinical or neurobiological, must account for the continuum nature of fibromyalgia to be valid," they argued in conclusion.
