Acquired C1 esterase inhibitor deficiency.

Acquired C1 esterase inhibitor deficiency is a rare condition associated with autoimmune or low-grade lymphoproliferative disorders. Adults or elderly patients are most commonly affected. The diagnosis is suspected when patients present with recurrent angioedema and low serum levels of C4 with normal levels of C3. Low levels of C1q and low C1 esterase inhibitor activity confirm the diagnosis. In this paper, we summarize experience with 22 cases of acquired C1 esterase inhibitor deficiency in the context of a review of the published literature on diagnosis and treatment of this condition.