Patient-reported joint tenderness and quality of life, the subjective components of the DAS28 disease activity score, are valuable in identifying fibromyalgia in patients with rheumatoid arthritis (RA).
Based on those two factors, researchers used a score called DAS28-P to distinguish between RA patients with fibromyalgia and those with simple RA.
The study, “The subjective components of the Disease Activity Score 28-joints (DAS28) in rheumatoid arthritis patients and coexisting fibromyalgia” was published in the journal Rheumatology International.
The coexistence of fibromyalgia increases disease activity and worsens pain, mental health, and response to treatment in RA patients, according to several studies, including results from the large ESPOIR cohort of early RA patients.
Fibromyalgia can cause confusion in evaluating RA disease activity scores, as patients may complain more about joint tenderness and their overall health.
A study done with early RA patients suggests that Disease Activity Score 28-joints (DAS28) — a well-established tool to address disease activity in RA — may be influenced by the presence of fibromyalgia, particularly the patient-reported components of the score.
DAS28 includes patient-reported counts of tender and swollen joints from a list of 28, plus laboratory measurements of erythrocyte sedimentation rate (ESR) or C-reactive protein — blood markers of inflammation — and a patient-reported assessment of quality of life.
Researchers conducted the study to discern the impact of fibromyalgia on the subjective components of the DAS28 and investigate whether these could be used to distinguish patients with fibromyalgia RA from those with RA alone.
The study included 292 RA patients with moderate to high disease activity, in treatment with conventional or biological disease-modifying anti-rheumatic drugs.
The patients were 63 years old on average, and had a mean disease duration of 11.6 years. They were recruited from an outpatient clinic of a rheumatology center in Italy.
All were tested for ESR, C-reactive protein, and RA blood biomarkers. The DAS28 score and a shorter version (DAS28v3) without the overall health assessment were calculated for each patient.
They also completed two surveys: Recent-Onset Arthritis Disability (ROAD) and the Rheumatoid Arthritis Disease Activity Index (RADAI).
A significant portion of the RA patients (14.7%) also had fibromyalgia. Compared to patients with RA only, those with fibromyalgia reported stronger disability (ROAD) and higher disease activity — measured either by RADAI or DAS28. They also complained of worse overall health, joint tenderness, and pain.
Values of DAS28-P were also significantly raised in fibromyalgic RA. The score also correlated strongly with disease activity indexes (DAS28, DAS28v3 and RADAI) and, to a lesser extent, with disability reports (ROAD). The higher the DAS28-P scores, the greater the other scores.
The diagnostic ability of DAS28-P was considered “very good” to distinguish patients with simple RA from those with fibromyalgia, reaching a sensitivity of 81.4% and a specificity of 80.3%.
Its positive likelihood ratio was 4.14, meaning that DAS28-P is over four times more likely to be correct when classifying an RA patient as fibromyalgic.
Pain is still a major problem for RA patients, and patients tend to underscore their need for relief.
But for that, reliable instruments to measure disease activity are required. Although active inflammation contributes to pain, other sources of pain such as fibromyalgia can lead to misinterpretation of disease activity.
“DAS28 of patients whose assessments are discordant with those of their physicians may not accurately reflect disease activity.” the researchers wrote.
To overcome that, the DAS28-P “may be a convenient and useful means of identifying patients with fibromyalgic RA and selecting patients for specific treatments,” they added.