BACKGROUND
Angioedema is a rare manifestation of systemic lupus erythematosus (SLE) that can lead to life-threatening complications, including airway compromise. Acquired angioedema is classically associated with C1 esterase inhibitor (C1-INH) deficiency caused either by increased consumption of C1-INH or the development of autoantibodies against C1-INH. However, emerging reports describe patients with active SLE who develop recurrent angioedema despite preserved C1-INH levels and function, suggesting a possible complement-mediated or bradykinin-associated inflammatory phenotype that remains incompletely characterized.
CASE REPORT
We report the case of a woman in her early 20s with SLE and lupus nephritis who presented with a urinary tract infection and unilateral periorbital edema. Initial laboratory evaluation revealed anemia, thrombocytopenia, and acute-on-chronic kidney injury. She was treated with antibiotics for presumed urinary tract infection and preseptal cellulitis. During hospitalization, she developed laryngeal edema requiring prompt treatment with intravenous dexamethasone, with rapid clinical improvement. Further evaluation demonstrated low C4 and C1q complement levels, elevated C1q complement binding levels, elevated anti-C1q antibodies, and preserved C1-INH antigen and functional levels, raising suspicion for complement-mediated angioedema occurring in the setting of active SLE. Over the ensuing 6 months, she experienced recurrent episodes of angioedema with progressive renal dysfunction and concern for evolving macrophage activation syndrome or severe hyperinflammatory immune activation.
CONCLUSIONS
This case highlights a rare presentation of recurrent angioedema associated with active SLE and complement activation despite preserved C1-INH levels and function. The case underscores the importance of early recognition of airway involvement in patients with lupus and illustrates the diagnostic challenges surrounding complement-mediated angioedema phenotypes in autoimmune disease.

Keywords: Angioedema; Complement C1q; Lupus Erythematosus, Systemic; Macrophage Activation Syndrome