title: Unmasking of acquired autoimmune C1-inhibitor deficiency by an angiotensin-converting enzyme inhibitor.
abstract: BACKGROUND
  A majority of angioedema arise from unknown etiologies. Angioedema may also arise from medications or deficiency of C1-esterase inhibitor (C1-INH); either of these may lead to recurrent, sometimes life-threatening attacks of subcutaneous or submucosal edema if the angioedema involves the tongue, throat, or larynx. We describe a patient with unknown acquired C1-INH deficiency, who experienced only mild attacks of angioedema before treatment with an angiotensin-converting enzyme (ACE) inhibitor. This therapy led to life-threatening respiratory distress.
  
  
  OBJECTIVE
  To investigate this patient's life-threatening angioedema.
  
  
  METHODS
  Serum protein electrophoresis and immunofixation were performed. The titer of anti-C1-inhibitor autoantibody was determined by ELISA, and the specificity of the autoantibody demonstrated by using purified C1-INH to block binding in the ELISA. Finally, fractions from the immunoelectrophoresis gel were tested for C1-INH autoantibody by ELISA.
  
  
  RESULTS
  Complement activation was documented by reduced C1-INH, C1q, and C4, and the patient was found to have an autoantibody of IgG2 isotype specific for C1-INH. After discontinuation of the ACE inhibitor, he continued to have decreased C1-INH and positive C1-INH autoantibodies.
  
  
  CONCLUSIONS
  This case describes a patient who had a history of mild facial and extremity swelling with abdominal symptoms before ACE inhibitor treatment; this medication resulted in life-threatening respiratory distress. The use of the ACE inhibitor may have unmasked this patient's acquired autoimmune C1-INH deficiency.
authors.affiliation: Division of Clinical Immunology, Mount Sinai-New York University Medical Center, New York, USA. klein014@mc.duke.edu
authors.forename: G I
authors.initials: GI
authors.lastname: Kleiner
authors.forename: P
authors.initials: P
authors.lastname: Giclas
authors.forename: G
authors.initials: G
authors.lastname: Stadtmauer
authors.forename: C
authors.initials: C
authors.lastname: Cunningham-Rundles
mesh_terms: D000368:Aged; D000799:Angioedema / Q000276:immunology*; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000009:adverse effects*; D000911:Antibodies, Monoclonal / Q000276:immunology; D001323:Autoantibodies / Q000276:immunology; D001327:Autoimmune Diseases / Q000276:immunology*; D001797:Blood Protein Electrophoresis; D003174:Complement C1 Inactivator Proteins / Q000172:deficiency* / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis / Q000276:immunology; D008297:Male
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D003174:Complement C1 Inactivator Proteins; D007074:Immunoglobulin G