AE without urticaria can be non-histamine mediated due to C1 inhibitor (C1-INH) deficiency (hereditary or acquired), or related to angiotensin converting enzyme (ACE) inhibitor use, autoimmune diseases, malignancies, or nonsteroidal anti-inflammatory drug (NSAID) use, but in many cases is idiopathic. Here, ACE is linked to autoimmune disease.