Acquired C1 esterase inhibitor deficiency
Acquired C1 esterase inhibitor deficiency, also referred to as acquired angioedema (AAE), is a rare medical condition that presents as body swelling that can be life threatening and manifests due to another underlying medical condition. The acquired form of this disease can occur from a deficiency or abnormal function of the enzyme C1 esterase inhibitor (C1-INH). This disease is also abbreviated in medical literature as C1INH-AAE. This form of angioedema is considered acquired due to its association with lymphatic malignancies, immune system disorders, or infections. Typically, acquired angioedema presents later in adulthood, in  contrast to hereditary angioedema which usually presents from early childhood and with similar symptoms. Acquired angioedema is usually found after recurrent episodes of swelling and can in some cases take several months to diagnose. Diagnosis usually consists of medical evaluation in addition to laboratory testing. Laboratory evaluation includes complement studies, in which typical cases demonstrate low C4 levels, low C1q levels, and normal C3 levels. Determining the etiology, or cause, of acquired angioedema is often helpful in providing appropriate management of AAE. Management of AAE usually includes treating any underlying disorder that could be responsible for the condition. Additionally, symptom  management is important, especially in cases that are life threatening. There are medications available to treat AAE, which are focused on replacing deficient levels of C1-INH or abnormal C1-INH enzymes. There are some cases of partial improvement and full resolution with treatment of the underlying medical problems contributing to AAE. Epidemiology. It is estimated that the worldwide prevalence of AAE ranges from 1 person in every 10,000 people are affected to 1 case in every 150,000 people. However, it is thought that this disease prevalence could be higher due to diagnostic oversight and the shared symptoms of acquired  angioedema with similar diseases. This disease tends to affect males and females equally. Additionally, individuals with acquired angioedema usually develops symptoms in their fourth decade of life or older. Of note, Saini reports the difficulty of diagnosing angioedema accurately due to certain challenges. These obstacles include the lack of awareness about angioedema presentation and potentially higher than expected worldwide prevalence. More challenges include the similarities to paraneoplastic disorders that often require higher priority of care, the evolution of symptoms over time, and mild cases might be attributed to medication use or allergic reactions from an individual's existing medical history . As a result, accurate diagnosis of AAE can take several months, which can delay targeted and specific treatment. Causes. There are various disease comorbidities associated with acquired C1 esterase inhibitor deficiency, including: Pathophysiology. The C1 esterase inhibitor (C1-INH) enzyme plays a role in the classical pathway of the complement cascade, which is a component of the immune system response that acts to protect the human body from a variety of foreign substances. As shown in the figure above, the complement cascade starts with the C1q protein which binds to an antibody-antigen complex that arises during an immune response  to an invading substance. When the complex is signaled for activation, or turned on, then downstream proteins in the complement cascade are activated, including complement component 2 (C2), complement component 3 (C3), and complement component 4 (C4). When these particular enzymes such as C3 and C4 are activated, their subsequent signals lead to an inflammatory response that involves localized edema, or swelling. The role of C1-INH is to regulate and control the activities of the complement cascade, such that complement proteins remain in check and do not lead to unnecessary activity. When there is a deficiency of C1-INH  due to one of the previously mentioned causes, then the complement cascade remains continuously activated and can lead to potentially life-threatening swelling. Clinical Presentation. Acquired angioedema presents as mucosal swelling on external and/or internal surfaces of the body. Typical areas of swelling include the face, arms, and legs, while internally some individuals have swelling of the tongue and upper airways. In contrast to hereditary angioedema, there tends to be less symptoms of the abdomen or gastrointestinal tract, but symptoms of nausea, vomiting, and diarrhea have been seen in acquired angioedema. Although this condition appears similar to other skin conditions  in which swelling occurs, acquired angioedema does not lead to itchy skin (pruritus) or hives (urticaria). Diagnosis. Acquired angioedema is diagnosed through a supportive clinical examination usually in addition to laboratory evaluation. The clinical history consists of recurrent angioedema episodes, symptom onset after 30 years of age, and negative family history of hereditary angioedema. Laboratory evaluation typically consists of complement studies, genotyping, and/or checking for antibodies against C1INH. The most useful complement studies obtained are as follows: To help confirm cases of acquired angioedema, the following pattern of complement studies are observed: low C4 level, low C1-INH protein level , low C1q level, and decreased C1-INH protein function. Using the diagnostic approach mentioned here and in the figure shown above, acquired angioedema is categorized into subtypes for targeted management. The following subtypes include: AAE-I, AAE-II, sex-hormone dependent AAE, and drug-induced AAE. AAE-I subtype groups paraneoplastic syndrome or B-cell malignancies that lead to destruction of the C1-INH enzyme causing acquired angioedema. AAE-II subtype groups autoimmune disorders, such as systemic lupus, causing acquired angioedema. Sex-hormone dependent AAE is associated with case reports of individuals with abnormally elevated estrogen levels or in cases  where physiologically elevated estrogen is expected as in pregnancy. Drug-induced AAE can be triggered by certain medications, including ACE inhibitors or angiotensin receptor blockers. Furthermore, additional laboratory testing can be done to consider other causes of swelling that appear similar to angioedema. Some of the common differential diagnoses for angioedema include: allergic reactions, contact dermatitis, skin and soft tissue infections (i.e. cellulitis), lymphedema, and foreign body aspiration. Management. Treatment of acquired angioedema is separated into two main parts. First controlling acute symptoms during angioedema attacks is crucial for preventing and lowering the risk of mortality. Second, managing AAE chronically  with prophylactic treatment is important to improve prognosis and quality of life. Both pharmacologic therapies (i.e. medications) and symptom management can be used in both acute and chronic treatment of AAE. Pharmacologic treatment in acute situations consists of replacing the enzyme concentrate that is deficiencent or dysfunctional in this disease process. In life threatening situations, including cases of oral and pharyngeal swelling, it is important to manage these symptoms and to protect the airways in order to lower the risk of mortality. Typical treatments for anaphylaxis and allergic reactions, such as epinephrine, corticosteroids, and antihistamines, are often used in acute  cases of AAE with variable resolution. C1-INH concentrates are available in intravenous (IV) and intramuscular (IM) methods of delivery. C1-INH concentrate therapy has shown considerable efficacy (or effect) in acute and prophylactic treatments of hereditary angioedema, but has varying levels of efficacy in AAE. For prophylaxis, clinicians focus on controlling underlying underlying disorders, such as those mentioned under causes, that could be contributing to AAE pathophysiology. Beyond controlling comorbidities, angioedema is usually managed through medications to prevent attacks and to reduce the number of attacks. C1-INH concentrate can be used to replace deficient or abnormal C1-INH  enzyme with considerable efficacy. The following list of medical therapies have been used for prophylaxis, including androgens, tranexamic acid, and monoclonal antibody such as rituximab. These agents all have varying roles, efficacy, and potential risks through their use. Prognosis. The evaluation of acquired angioedema usually prompts an investigation into the underlying cause. As mentioned in the causes section, malignancy or autoimmune disorders are the more common causes, which must be further explored and considered for treatment if found in an individual. Prognosis depends on the underlying disorder, which may be found at the time of initial diagnosis or through ongoing  monitoring. Additionally, successful treatment of the underlying disorder has been observed in some cases to resolve acquired angioedema from partial to complete remission.