SAN FRANCISCO — Fibromyalgia in the presence of rheumatoid arthritis (RA) was associated with greater declines in functional status compared with RA without fibromyalgia, Canadian researchers reported here.
In a prospective observational study, RA patients with fibromyalgia had a significantly larger increase in their Multidimensional Health Assessment Questionnaire (MDHAQ) score from baseline to 2 years than RA patients without fibromyalgia, according to Hyein Kim, MD, of Western Reserve University in London, Ontario, and colleagues.
"Pain in RA is an important clinical feature because it is the primary reason why a lot of our RA patients seek medical attention, and it is often a highest priority for improvement for a lot of the patients as well," Kim said during a presentation at the American College of Rheumatology meeting.
"These patients often have ongoing pain despite being treated with anti-tumor necrosis factor agents in both the articular and non-articular sites," she added.
Although pain in RA is often considered to have an inflammatory origin, pain correlates poorly with measures of inflammation such as erythrocyte sedimentation rate, C-reactive protein, and swollen joint count. "Fibromyalgia is the prototypical non-inflammatory pain condition," Kim said.
The prevalence of fibromyalgia in RA is about 20% compared with about 2.5% in the general population. Functional status is one of the most significant predictors of future outcome in RA. Compared with RA without fibromyalgia, patients with both diseases have higher disease activity, worse quality of life, and worse functional status, although studies with these endpoints were limited by their cross-sectional design.
She and colleagues assessed the impact of fibromyalgia on 2-year changes in functional status of RA patients in a prospective study. The study participants were a subgroup of 156 patients who participated in the Brigham and Women's Hospital Rheumatoid Arthritis Sequential Study. They completed a questionnaire every 6 months and underwent yearly physical examinations and laboratory tests.
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Overall, the mean age of the study participants was 58.5 and 85.9% were female while 93.6% were Caucasian. Mean RA disease duration was 15.4 years.
The primary outcome was the change in MDHAQ score from baseline to 2 years. MDHAQ assesses physical function, pain, and global status, and is scored on a scale of 0 to 3, with 3 indicating the worst functional status. The primary predictor for the study was fibromyalgia status as a dichotomous variable, with fibromyalgia defined as a score ≥13 on the Fibromyalgia Symptom Scale. This scale has two components, one that assesses widespread body pain and the other that assesses somatic symptoms, with scores ranging from 0 to 12, with higher scores indicating more severe symptoms.
Of the 156 RA patients included, 26 also had fibromyalgia. Compared with RA patients without fibromyalgia, those with fibromyalgia had significantly higher baseline mean scores on the disease activity score using C-reactive protein (2.8 versus 3.6, P=0.01), higher baseline widespread pain on the Fibromyalgia Symptom Scale (6.5 versus 16.4, P<0.001), higher MDHAQ scores (0.3 versus 0.7, P<0.001), and higher Hospital Anxiety and Depression Scale scores (8.2 versus 13.7, P<0.001).
In an adjusted multivariable linear regression model, RA patients with fibromyalgia had a 0.14-unit greater increase in MDHAQ score over 2 years than RA patients without fibromyalgia (P=0.02). In a secondary analysis examining the association between continuous Fibromyalgia Symptom Scale score and change in MDHAQ, higher fibromyalgia scores were significantly associated with greater 2-year increases in MDHAQ score (β coefficient 0.013, P=0.01).
Kim said the difference is striking given that the expected MDHAQ score increase in established RA patients is only 0.02 to 0.032 over 2 years.
"Formal assessment of fibromyalgia characteristics in RA patients may be beneficial and it may identify a subgroup of patients who are more likely to experience further worsening in functional status over time," she said.
Kim disclosed no relevant relationships with industry.
Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered preliminary until published in a peer-reviewed journal.
Primary Source: American College of Rheumatology, September 29, 2015. By Kim H, et al., Fibromyalgia Predicts Two-Year Changes in Functional Status in Rheumatoid Arthritis Patients.