Background The Disease Activity Score including 28 joint count (DAS-28) is the most widely used outcome measure in RA. However, despite evidence that metatarsophalangeal (MTP) joints are often the first joints affected in RA, DAS-28 score does not incorporate them.
Objectives Our study aimed to investigate the correlation between DAS-28 assessment and objective evidence of active joint inflammation using the US examination of both hands and feet, including wrists, metacarpophalangeal (MCP), proximal interphalangeal (PIP), and MTP joints.
Methods A retrospective study was conducted, including 87 patients who were referred to the US clinic for an examination of their hands and feet in the last 6 months (46 patients with RA and 43 controls - patients with other inflammatory or degenerative arthropathies). Information about demographics, disease duration, current treatment, inflammatory markers, and DAS-28 scores was captured. The US OMERACT criteria were used for grading synovial hypertrophy, and assessing for the presence of Power Doppler (PD) signal, erosions and osteophytes. Statistical analysis methods included T-test, Mann-Whitney U test, Z score for proportions and Spearman's correlation coefficients.
Results In the RA group, DAS-28 had a weakly positive correlation with the cumulative PD scores of their hands and feet joints (R=0.14, P=0.02), but did not correlate with PD score of MTP joints (R=0.03, P=0.09). In the control group, DAS-28 did not correlate significantly with either the total PD scores of feet (R=0.42, P=0.26) or hands and feet joints (R=0.5, P=0.25). Sensitivity of US examination of hands alone compared to hands and feet was 74.3% for the RA group, while the sensitivity of US feet to detect the presence of PD was 59.2% when compared to the US of both hands and feet.
Conclusions We found that DAS-28 correlated poorly with objective evidence of inflammation as detected by US of the hands and feet, and this correlation was lost when only the presence of inflammation in the feet was taken into consideration. Further validation of our results in a larger study including patients stratified based on the disease duration might help understand which patient subgroups are more likely to have their disease activity significantly under-evaluated using DAS-28 outcome measure.
Disclosure of Interest None declared