Background Pain is a central characteristic of rheumatoid arthritis (RA) and axial spondyloarthritis (axSpA), but it is multifactorial. Some patients describe high fluctuation of pain intensity, but fluctuation of pain and its association with disease activity has been little investigated.
Objectives To compare the variability of pain and of self-reported disease activity in patients with RA or axSpA through repeated assessments, and to describe clinical characteristics of patients with high variability of pain.
Methods Data were extracted from a prospective cohort study (ActConnect) including patients with clinician-confirmed RA or axSpA owning a smartphone.1 Baseline characteristics were collected. Over 3 months, weekly self-assessments of pain and patient global assessment of disease activity on 0–10 points numerical rating scales (NRS) were obtained. For each patient, the mean of the inter-assessment differences of NRS (average of absolute change – AAC) of pain and disease activity were calculated. RA and AxSpA patients were compared by t-test. High variability was defined as the upper tercile of AAC. Pearson’s correlation was used to evaluate the correlation between variability of pain and of self-reported disease activity. Univariate and multivariate logistic regression compared patients with high vs low variability of pain, without imputation of missing data, on R, including weekly self-reported flare over follow-up.
Results Eighty-six patients with RA and 79 with axSpA were included, mean age was respectively 48.7 (SD 12.7) and 41.7 (SD 10.2) years, mean disease duration was 8 (SD 8.8 and 8.6 respectively) years, 81% and 44% respectively were female. Mean DAS28 and BASDAI were respectively 2.27 (SD 1.18) and 3.21 (SD 2.06) at baseline; 44% and 62% respectively of patients were receiving a biologic.
Mean levels of pain and patient global assessment of disease activity were non-significantly higher in AxSpA than RA patients (table 1) and variability of pain and disease activity were also higher in AxSpA (table 1). Correlation between AAC of pain and activity was 72% in RA, and 84% in AxSpA. In multivariate analyses, self-reported flares were the only determinant of pain AAC (Odds ratio 2.25 [1.27–4.38] p=0.01 and 3.26 [1.67–6.35] p<0.001 respectively for RA and axSpA).
Conclusions In this population of overall well-controlled patients, close repeated assessments of pain showed relatively low fluctuations of pain in RA and axSpA (around 1 point on a 0–10 scale). Patients with axSpA reported slightly more pain, self-reported disease activity and fluctuations of these outcomes, than patients with RA. Fluctuations in pain were highly correlated to fluctuations in patient global assessment of disease activity, indicating significant overall between these 2 patient-reported outcomes. Self-reported flares were the main element explaining fluctuations in pain, confirming the validity of self-reported flares.
Reference  Jacquemin C, Molto A, Servy H, et al. Flares assessed weekly in patients with rheumatoid arthritis or axial spondyloarthritis and relationship with physical activity measured using a connected activity tracker: A 3-month study. RMD Open2017;3:1–8.
Disclosure of Interest None declared
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