Belimumab in refractory lupus serositis: a multicenter case series highlighting pleural, pericardial and rare peritoneal involvement

Abstract Background Serositis is a well-recognized manifestation of systemic lupus erythematosus (SLE), most commonly affecting the pleura and pericardium, while lupus peritonitis remains a rare and underreported entity. Management of refractory cases remains challenging, particularly in patients with steroid dependence or inadequate response to conventional immunosuppressive therapy. Objective To describe the clinical course and potential steroid-sparing effect of belimumab in patients with refractory lupus serositis, including rare peritoneal involvement. Methods We report a multicenter case series of four patients with systemic lupus erythematosus (SLE)-associated serositis refractory to standard immunosuppressive therapy, identified from three tertiary rheumatology centers in two countries. Clinical, laboratory, and disease activity outcomes using the Safety of Estrogens in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI) were assessed before and after initiation of belimumab. Baseline and follow-up laboratory parameters, imaging findings, and SELENA-SLEDAI scores were reviewed for all patients whenever available. Prior to initiation of belimumab therapy, all patients underwent screening for hepatitis B, hepatitis C, human immunodeficiency virus (HIV), and latent tuberculosis according to institutional biologic therapy protocols. Results All patients showed clinical improvement after belimumab initiation, with reduction or resolution of serosal inflammation across pleural, pericardial, and peritoneal sites. Disease activity scores improved in all patients, with SELENA-SLEDAI decreasing from baseline values of 8–12 to 0–2 during follow-up. Corticosteroid tapering was successfully achieved in all cases. Conclusion Belimumab may be a useful steroid-sparing add-on option in selected patients with refractory lupus serositis, including rare cases of lupus peritonitis. This multicenter case series adds real-world clinical experience to the limited literature on B-cell activating factor (BAFF) inhibition in serosal manifestations of SLE. Larger studies are needed to further evaluate its role in this setting.