Fibromyalgia should be seen as one, not two disorders

The symptomatology and severity of fibromyalgia is virtually identical among people with primary and secondary forms of the disorder, researchers say, and the two should therefore be considered the same.

Currently, patients classified as having primary fibromyalgia have a defined set of pain, fatigue, cognitive, and psychological symptoms in the absence of a clinically important inflammatory disorder, while secondary fibromyalgia occurs in the context of a disease such as rheumatoid arthritis.

In research published online in the Journal of Rheumatology, investigators led by Frederick Wolfe, MD, of the National Data Bank for Rheumatic Diseases and the University of Kansas in Wichita, sought to understand whether patients with primary and secondary diagnoses “had the same level of outcomes, symptoms, and characteristics” at different points across the polysymptomatic distress (PSD) scale, a measure to assess severity in fibromyalgia.

The PSD is calculated by combining two measurements used in fibromyalgia: the widespread pain index (WPI), which counts the number of painful regions in the body, and the somatic symptom scale (SSS), which measures fatigue, sleep, emotional and cognitive problems, and the extent of symptom reporting. Higher PSD scores correlate to worse outcomes, including for disability and health-related quality of life.

Dr. Frederick Wolfe

Dr. Wolfe and his colleagues compared records from 1,525 patients (mean age 57, 95% women) in the National Data Bank who were diagnosed with fibromyalgia only, with those from 12,037 people with rheumatoid arthritis (mean age 61, 82% women) and not evaluated for fibromyalgia. They also looked at data on fibromyalgia symptoms from a general population sample in Germany.

A total of 22% of the RA patients in the cohort met the criteria for a fibromyalgia diagnosis under current (2016) ACR criteria, while 53% of the patients in the primary fibromyalgia group and 2.0% of the general population sample did. Symptom magnitude and severity differed only slightly between the RA and fibromyalgia-only groups, the investigators found. Those without RA had a mean PSD score of 21.9 (of a possible 31) and those with RA and who met the fibromyalgia criteria had a mean score of 20.7.

The researchers found that the disease behaved similarly whether it occurred alone or with RA. Patients with higher PSD scores experienced worse outcomes across symptom domains regardless of RA status. When controlled for PSD, pain, patient global, and health-related quality of life, scores were similar between groups. However, disability scores and painful joint counts were slightly higher in the RA group.

“Fibromyalgia can exist whether or not there’s another disorder present,” Dr. Wolfe said in an interview, “but we don’t tend to think of it that way.” Clinicians, Dr. Wolfe said, “have to be able to identify [fibromyalgia] within other disorders. It can’t be only something that you find once you’ve ruled out everything else.”

Clinicians can look to PSD scores to inform management choices, the researchers said, instead of whether the fibromyalgia is considered primary or secondary.

Dr. Wolfe said that the current bifurcated concept of the disease also creates difficulties for research into fibromyalgia treatments. For example, using RA patients as a comparator group in a clinical trial is problematic because RA patients, as this study demonstrates, also have a substantial burden of fibromyalgia. And the use of so-called healthy controls in fibromyalgia studies is also a problem, Dr. Wolfe said.

“People say they’ve tried this drug or treatment in people with fibromyalgia and on normal controls. But there’s no such thing as normal controls for fibromyalgia. Does normal mean people with zero fatigue or pain? Or do we look at what’s normal among people who have multiple sclerosis or RA? If you’re going to test things in people with fibromyalgia, you never really have normal controls because it depends on where in this whole continuum you are.”

But what this new research also shows, he said, is that while up to now “you couldn’t easily study people with fibromyalgia [in other disorders], it doesn’t matter if you have RA or another disorder in addition to fibromyalgia. You get the full spectrum or severity regardless. The underlying disease wouldn’t affect your identification of the fibromyalgia symptoms.”

Dr. Wolfe and his colleagues described as a limitation of their study the lack of comparator groups besides RA patients. Secondary fibromyalgia is also commonly reported with osteoarthritis, they noted.

The study had no outside funding and investigators reported no conflicts of interest.

SOURCE: Wolfe F et al. J Rheumatol. 2018 Jul 15. doi: 10.3899/jrheum.180083.