Background: Belimumab was the first biological drug approved for the treatment of systemic lupus erythematosus (SLE) patients. Phase II/III randomized controlled trials and real-life studies identified patients with musculoskeletal involvement as best responders.

Objective: To evaluate the effectiveness of belimumab in SLE-related joint involvement.

Methods: The cohort comprised SLE patients receiving belimumab for musculoskeletal indications. Belimumab was intravenously administrated according to protocols; all the patients were evaluated at baseline (T0) and after 3 (T1), 6 (T2), and 12 (T3) months. We assessed joint activity by disease activity score 28, simple disease activity index (SDAI), clinical disease activity index (CDAI), and swollen tender ratio. Each patient underwent musculoskeletal ultrasound of 34 joints to assess synovial effusion synovial hypertrophy, and power Doppler; by using a semi-quantitative scale (0–3) we obtained the total inflammatory score (0–216).

Results: We evaluated 20 patients (males/females 1/19, median age 45 years [interquartile range (IQR) 12], median disease duration 144 months [IQR 144]). CDAI and SDAI significantly decreased at T1 (P = 0.02 and P = 0.01 respectively) and this improvement was maintained at the following time-points (CDAI: T2 P = 0.008, T3 P = 0.004; SDAI: T2 P = 0.006, T3 P = 0.01). A significant reduction of median ultrasound score was identified at T1 (T0 20.5 [IQR 13.5] vs. T1 7.5 [IQR 4.7], P < 0.001), and maintained at T2 (7.0 [IQR 5], P < 0.0001), and T3 (7.0 [IQR 9.0], P < 0.0001).

Conclusions: Belimumab induces a sustained improvement of ultrasound-detected inflammatory status at the articular level.