Tender joint count may not be a reliable indicator of ongoing inflammation in patients with established rheumatoid arthritis (RA), according to research published in the Annals of the Rheumatic Diseases.

Through post hoc analyses of 209 patients with RA, researchers set out to examine the relationship between ultrasound synovitis and joint swelling and tenderness, and patient-reported joint pain, at both the patient and joint level. Patients underwent examination 6 times in a 12-month period, where 32 joints in both upper and lower extremities were assessed for joint swelling and joint tenderness, using both grayscale and power Doppler ultrasound.

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The patient cohort was 81% women, with a mean age of 53.3±13.2 years and a 10±8.8 year disease duration. Median tender and swollen joint counts were 5 and 6, respectively (range 2-11 and 3-11). The sum of patient-reported joint pain scores was 17 (range 7 to 32), and the sum of grayscale and power Doppler scores was 26 and 10, respectively (range 16 to 41 and 3 to 21). Disease Activity Score in 28 joints was 4.5 (range 3.6 to 5.5).

On a patient level, tender joint count was most highly correlated with the patient-reported joint pain sum score; conversely, the relationship with swollen joint count “ranged from weak to moderate and negligible” for the grayscale and power Doppler sum scores. However, during follow up, swollen joints “strongly correlated” with these scores.

More than 4100 joints were assessed at baseline (n=4131), with 11% of joints only tender, 14.5% of joints only swollen, 12.1% of joints both tender and swollen, and 62.5% of joints neither tender nor swollen. In terms of ultrasound, a grayscale score of ≥2 was detected in 27.9% of joints, and a power Doppler score of ≥1 was found in 25.2% of joints.

Ultimately, 51.1% and 46.5% of tender joints had ultrasound synovitis at baseline and all visits; similar concordance was found with patient-reported joint pain and ultrasound synovitis (45.3% and 42.1%). Swollen joints had a higher prevalence of ultrasound synovitis (75.7% and 76.4%). Nontender joints and joints without patient-reported joint pain had ultrasound synovitis at baseline and all visits in 25.9% and 21%, and 20.8% and 17.7% of joints, respectively. Similarly, nonswollen joints had ultrasound synovitis in 15.8% and 14.6% of joints.

Upon assessment of all joints, researchers of the study noted an increased percentage of swollen-only joints with higher grayscale and power Doppler scores; a similar increase was not noted in tender-only joints.

Limitations to the study included the single-center design, which limits the generalizability of findings, and the inclusion only of patients with established RA. Finally, the researchers said that there may be limitations of ultrasound “to detect small pathologies that could cause extracapsular joint tenderness.”

The researchers of the study concluded, “Swollen joints were strongly associated with ultrasound detected synovitis at both [the] patient and joint level. These results may question if tender joints reflect ongoing inflammation in established RA.”

Multiple researchers report relationships with the pharmaceutical industry. For a complete list of disclosures, please see the full text of the study online.

Hammer HB, Michelsen B, Sexton J, et al. Swollen, but not tender joints, are independently associated with ultrasound synovitis: results from a longitudinal observational study of patients with established rheumatoid arthritis [published online June 6, 2019]. Ann Rheum Dis. doi: 10.1136/annrheumdis-2019-215321