Disease activity score for twenty-eight joints reflects different distribution of the inflammation as seen on ultrasound: A comparative ultrasound study in early rheumatoid and psoriatic arthritis.

Objectives: To assess the correlations of different ultrasound (US) indices with disease activity score for 28 joints (DAS28) in patients with early rheumatoid (RA) and psoriatic arthritis (PsA).

Methods: The study involved 105 patients with early arthritis - 82 patients with RA and 23 with PsA. A comprehensive US examination was performed, including bilateral evaluation of the wrists, metacarpophalangeal II-V and proximal interphalangeal joints II-V, extensor compartments IV and VI of the wrists, and the flexor tendons of digits II-V. Both gray scale US (GSUS) and power Doppler US (PDUS) modalities were utilized, and the following scores were systematically recorded for each participant: Synovitis, Mini-enthesitis and Finger Flexor Tenosynovitis Score.

Results: In RA patients, PDUS synovitis score demonstrated the strongest relationship with DAS28 (rs = 0.829), followed by the GSUS synovitis score (rs = 0.794). The associations with IV extensor compartment tenosynovitis and VI extensor compartment tenosynovitis were of low magnitude. In the group of PsA patients, DAS28 showed significant positive correlations with the pseudotenosynovitis (rs = 0.515), central slip enthesitis (rs = 0.446), and finger flexor tenosynovitis (rs = 0.434) scores.

Conclusions: US-detected synovial inflammation accounts for the disease activity in RA, whereas inflammation of the hand mini-entheses and finger tendons has the greatest impact on DAS28 in PsA. Key Points • Ultrasound (US) of the joints, tendons and mini-entheses shows different distribution of the inflammation in patients with early rheumatoid (RA) and psoriatic arthritis (PsA). • The correlation between the Disease Activity Score for 28 joints (DAS28) and the synovitis scores on gray scale (GS) and power Doppler US (PDUS) in RA, and with the mini-enthesitis score in PsA, indicates distinct inflammatory patterns. In RA, disease activity predominantly reflects joint inflammation, whereas in PsA, it involves both articular and extra-articular components, including tendon and entheseal involvement. • Integrating US imaging with clinical assessments of disease activity may enhance rheumatologists' ability to identify distinct US-driven phenotypes, thereby supporting the development of personalized therapeutic strategies in the management of early arthritis.