D2.31 - A Case of Acquired C1 Inhibitor Deficiency Angioedema with Anti-C1q Antibodies in Systemic Lupus Erythematosus and Negative Exome Sequencing

Rational:Acquired angioedema (AAE) associated with C1 inhibitor (C1-INH) deficiency is a rare condition, often linked to lymphoproliferative or autoimmune diseases. We present a case of AAE in a patient with active systemic lupus erythematosus (SLE) and positive anti-C1q antibodies.

Anamnesis: A 20-year-old female with a medical history of Systemic Lupus Erythematosus (SLE) diagnosed in 2021 presented with recurrent angioedema involving  face, lips, and genitalia. The symptoms started  in 2024 with the first episode of lip swelling, which resolved spontaneously within 4 days. Treatment with a four-fold increase in antihistamine dosage and on-demand  use of glucocorticosteroids had no effect. Since 2025, the frequency of attacks increased to 1–2 episodes per week, affecting the face and genital area. The swelling was described as dense, not burning, non-pruritic, with a sensation of tightness. The edema resolved spontaneously within 3–4 days or were successfully treated with subcutaneous Icatibant.

No family history was reported. The SLE course was considered active.  

Laboratory Findings:

Markedly reduced complement levels were reviled: C4 – 0.03 g/L (0.1–0.4), C3 – 0.38 g/L ( 0.9–1.7). C1-INH quantitative 0.171g/l (0.21 – 0.43) C1-INH functional 131% ( 70-130).Elevated anti-C1q IgG antibodies – 43 AU (<10). Positive ANA (6.9) and anti-dsDNA (98.73 U/mL). Total IgE was within normal range (14.4 IU/mL). Whole exome sequencing revealed no pathogenic variants.

Treatment:

Angioedema attacks were successfully  managed with subcutaneous icatibant (30 mg). Long-term management included tranexamic acid (1500 mg) for prophylaxis. SLE-specific treatment was continued with cyclophosphamide (600 mg IV every 2–3 weeks) following the absence of AEs.

Conclusion: This case highlights the importance of an individualized  therapeutic approach in patients with concurrent autoimmune disease and AAE association .