Abstract
DAS28 is interpreted as the inflammatory disease activity of RA. Non-inflammatory pain mechanisms can confound assessment. We aimed to examine the use of DAS28 components or DAS28-derived measures that have been published as indices of non-inflammatory pain mechanisms, to inform interpretation of disease activity.Data were used from multiple observational epidemiology studies of people with RA. Statistical characteristics of DAS28 components and derived indices were assessed using baseline and follow up data from British Society for Rheumatology Biologics Registry participants (1) commencing anti-TNF therapy (n = 10,813), or (2) changing between non-biologic DMARDs (n = 2992), (3) Early Rheumatoid Arthritis Network participants (n = 813), and (4) participants in a cross-sectional study exploring fibromyalgia and pain thresholds (n = 45). Repeatability was tested in 34 patients with active RA. Derived indices were the proportion of DAS28 attributable to patient-reported components (DAS28-P), tender-swollen difference and tender:swollen ratio. Pressure pain detection threshold (PPT) was used as an index of pain sensitisation.DAS28, tender joint count, visual analogue scale, DAS28-P, tender-swollen difference and tender:swollen ratio were more strongly associated with pain, PPT and fibromyalgia status than were swollen joint count or erythrocyte sedimentation rate. DAS28-P, tender-swollen difference and tender:swollen ratio better predicted pain over 1 year than did DAS28 or its individual components.DAS28 is strongly associated both with inflammation and with patient-reported outcomes. DAS28-derived indices such as tender-swollen difference are associated with non-inflammatory pain mechanisms, can predict future pain and should inform how DAS28 is interpreted as an index of inflammatory disease activity in RA.
Highlights
Disease activity score for 28 joints (DAS28) is interpreted as the inflammatory disease activity of RA
Datasets from four published studies were used to explore statistical characteristics of DAS28 components and derived indices of inflammatory or non-inflammatory disease activity; baseline data collected from participants in the British Society for Rheumatology Biologics Register (BSRBR) with active, established RA and a valid DAS28ESR score who were (1) initiating anti-TNF therapy (BSRBR anti-TNF cohort; n = 10,813) [13], or (2) changing between non-biologic disease modifying anti-rheumatic drugs (DMARDs, BSRBR-Control cohort; n = 2992) [14], (3) participants in the Early Rheumatoid Arthritis Network (ERAN cohort; n = 813) [15], and (4) participants undergoing routine care in a hospital-based, cross sectional study exploring FM status and pain pressure thresholds (PPT group; n = 45) [7]
Measurement properties of DAS28-Erythrocyte sedimentation rate (ESR), its components and derived indices Tender:swollen ratio underwent logarithmic transformation to give a closer approximation to a normal distribution
Summary
DAS28 is interpreted as the inflammatory disease activity of RA. We aimed to examine the use of DAS28 components or DAS28-derived measures that have been published as indices of non-inflammatory pain mechanisms, to inform interpretation of disease activity. The 28 joint disease activity score incorporating erythrocyte sedimentation rate (DAS28-ESR) is widely used as a measure of inflammatory disease activity in people with RA during clinical decision-making. Non-inflammatory mechanisms, through their effects on pain, can confound interpretation of DAS28-ESR ≥3.2 as a measure of active inflammation. Swollen joint count (SJC) and ESR are markers of inflammation. Tender joint counts (TJCs) might be increased in people with centrally augmented pain, and the visual analogue scale for global health (VAS-GH) might be high in people fulfilling fibromyalgia (FM) classification [6, 7].
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