The tender joint count (TJC) is included in composite disease activity scores (CDAS) (the Disease Activity Score in 28 joints, the Clinical Disease Activity Index, and the Simplified Disease Activity Index). The impact of having predominantly tender joints was explored by use of the Tender-Swollen Joint Count Difference (TSJD), and ultrasound (US) provided a measure of joint inflammation. The current study aimed to explore the cross-sectional and longitudinal associations between the TSJD and a spectrum of outcome measures, including US scores in patients with established rheumatoid arthritis (RA) during follow-up and while receiving treatment with biologic disease-modifying antirheumatic drugs (bDMARDs).
This was an observational study of 209 patients with established RA consecutively included upon initiation of bDMARD treatment and followed-up with clinical, laboratory, and comprehensive US examinations at 0, 1, 2, 3, 6, and 12 months. Patients were categorized into 2 groups: those with predominantly tender joints (TSJD >0) and those with predominantly swollen joints (TSJD ≤0). Statistical analyses included Pearson's correlation coefficient, an independent samples t-test, and regression analyses.
The TJC had high correlations only with patient-reported outcomes (PROMs) (P < 0.001). Levels from CDAS and PROMs were significantly higher (P < 0.001) at all visits in patients with TSJD >0 compared to those with TSJD <0. Laboratory markers and assessor's global visual analog scale scores were similar, and US sum scores were significantly lower (P < 0.001-0.03). The baseline TSJD positively predicted levels of all CDAS at 6 months (P < 0.001-0.019) but was a negative predictor of US sum scores (gray-scale and power Doppler) at 6 and 12 months (P < 0.001).
Patients with predominantly tender joints had higher CDAS but lower levels of inflammation as defined by US. These findings indicate that inclusion of the TJC in the CDAS may contribute to misleading information about inflammatory activity.