Successful Treatment of Acquired Angioedema Using B-lymphocyte Depletion Therapy Chang Na, MD, David Podell, MD, Christopher Randolph, David Dreyfus, Denise Kearney. Yale Primary Care Program, Waterbury, CT 1,2, Allergy, Asthma & Immunology, Waterbury, CT 3,4,5  Learning Objectives  Identify clinical manifestations of acquired C1 inhibitor (C1-INH) deficiency  Learn about the immunobiology underlying acquired C1-INH deficiency  Make treatment decisions based on mechanism of disease and the latest literature data  Case Description  Patient A: A 38 year old woman presented with seropositive deforming erosive rheumatoid arthritis (RA) and angioedema associated with acquired C1-INH deficiency.  Laboratory tests showed decreased C1q, C3, C4, and Ch50, worsening anemia, and elevated ESR.  She had a normal CT chest/abdomen/pelvis, normal SPEP, and flow cytometry that showed decreased CD4 and CD8 T cells but otherwise normal lymphoid phenotype.  Case Description Continued  Rituximab has been effective as adjunctive treatment of LPD, in particular B-cell lymphomas. Even though there was no associated LPD in our patients, they were successfully treated with B- lymphocyte depletion for acquired angioedema.  Rituximab appears to work by eliminating the clonal B lymphocyte population expressing a clonal Immunoglobulin G binding to C1 INH.  Anti-TNF agents such as adalizumab deplete B lymphocytes via effects on follicular dendritic cells and disruption of germinal center formation and maintenance.  B-lymphocyte depletion with humanized monoclonal antibodies such as rituximab or adalizumab appears to be an effective, long lasting therapy for acquired angioedema associated with a variety of autoimmune syndromes.  Learning Points  Discussion Continued  Patient C: A 41 year old woman with myasthenia gravis and anti- phospholipids syndrome, presented with angioedema and associated bowel and laryngeal edema requiring intubation.  Laboratory tests showed low C1q, C2, C3, C4 and anti-C1q antibody.  Clinical Course Thickened ascending colon  Discussion  After failure of other therapy including etanercept and corticosteroids (A), xolair (B), and kallekrein antagonist and corticosteroids (C), all three patients responded with complete remission of symptoms after B-lymphocyte depletion therapy with rituximab (A, C) or adalizumab (B).  The patients have been symptom free for 5 years, 3 years and 6 months thus far.  Acquired C1-INH deficiency is a rare condition which results in recurrent angioedema.  The condition is characterized by reduced C1-INH level or function, hyperactivation of the classical complement pathway, and bradykinin mediated recurrent angioedema.  Acquired C1-INH deficiency had been reported in association with lymphoproliferative disease (LPD) and autoimmune disorders.  The discovery of an auto-antibody IgG against C1- INH in patients with angioedema demonstrates that an auto-antibody mechanism may cause acquired C1- INH deficiency.  B lymphocytes appear to play a key part in the mechanism of action of acquired angioedema in a variety of autoimmune syndromes. Advanced rheumatoid arthritis with fusion of the carpal bones (yellow arrow). Metacarpal phalangeal joint subluxation (blue arrow).  Patient B: A 37 year old woman with Crohn’s disease and allergic asthma, presented with angioedema associated with wheezing and urticaria.  Laboratory tests showed elevated IgE levels and positive aeroallergen skin testing. A hematologic evaluation showed no evidence of lymphoma.  C1-INH deficiency is a rare condition resulting in recurrent angioedema episodes.  A lymphoproliferative autoimmune mechanism may cause acquired C1-INH deficiency.  Our cases highlight that B-lymphocyte depletion may be an effective treatment for acquired C1-INH deficiency