Background and aims Although both systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) may lead to the joint deformity, different characteristics such as the absence or the presence of bone destruction have been recognised as well. We aimed to clarify the difference of joint and tendon involvements between SLE and RA patients by using ultrasonography (US).

Methods Fifteen SLE with joint symptoms and 40 RA patients, who were treatment-naïve, were enrolled in this study. The wrist, metacarpophalangeal and proximal interphalangeal joints and related extensor/flexor tendons were ultrasonographically examined. Their joints and tendons were evaluated using a gray-scale (GS) for synovial thickening and synovial fluid retention, and power Doppler (PD) for blood flow according to a semiquantitative method based on a scale of grades 0 to 3, and patients graded with GS ≥2 or PD ≥1 were judged as having joint or tendon involvement.

Results Joint involvement was comparably observed in patients with SLE and RA (80% versus 95%, p=0.119). However, tendon involvement was more frequent in SLE than in RA (93% versus 65%, p=0.045), especially in the wrist joints (73% versus 40%, p=0.037). Moreover, when we investigated the intensity of US findings, the joint involvement score (GS+PD) per affected joint was lower in SLE than RA (2.0 versus 2.6, p=0.019), although tendon involvement score was similar (2.1 versus 2.2, p=0.738).

Conclusions As compared with RA, joint involvement is less intense and tendon involvement is more frequent in SLE with articular symptoms.