Acquired angioedema: Autoantibody associations and C1q utility as a diagnostic tool

Acquired Angioedema (AAE) is a rare condition classified into two subtypes: Type I, which is associated with lymphoproliferative disorders, and Type II, which is linked with autoantibodies against C1-esterase inhibitor (C1-INH). Unlike Type I AAE, Type II has no correlation with lymphoproliferative disorders. We report the evaluation of angioedema that was associated with an underlying lymphoproliferative disorder for the purpose of discussing the relationship between C1q and a diagnosis of AAE. A literature review was completed for the purpose of assessing the diagnostic value of C1q when used in the workup of AAE. A PubMed/Web of Science search (1976‐2010) produced 78 references (yielding 167 individual cases of AAE) using terminology “AAE.” The case described a patient with a depressed C1q (<3.5 mg/dL), decreased C4 (<3 mg/dL), decreased C1-inhibitor (1 mg/dL), decreased functional C1-INH (12%), and decreased total complement (<10 U/mL). Autoantibodies against C1-INH (free and bound respectively) were normal (12.4% and 10.1% of the standard of deviation). Using the above figures and data collected from the literature search, we tabulated 168 individual cases of AAE. Of the 168 cases, C1q was drawn in 104 cases, and 64 cases have no information regarding C1q. There are 10 cases where the C1q was documented as normal. With these values, a correlation between C1q and a diagnosis of AAE was assessed: A decreased C1q correlated with a diagnosis of AAE approximately 56%‐94% of the time. C1q is a useful tool when working up a case of AAE.