Angioedema (BE: angiooedema), also known by its eponym Quincke's edema, is the rapid swelling (edema) of the dermis, subcutaneous tissue, mucosa and submucosal tissues. It is very similar to urticaria, but urticaria occurs in the upper dermis.
In the past, angioedema was referred to by the term angioneurotic edema, which wrongly implied that the phenomenon was due to neurosis.
Cases where angioedema progresses rapidly should be treated as a medical emergency as airway obstruction and suffocation can occur. Epinephrine may be lifesaving when the cause of angioedema is allergic. In the case of hereditary angioedema, treatment with epinephrine has not been shown to be helpful.
Additionally, there are three autosomal dominant inherited forms known, due to mutations in the genes that control the clotting cascade, including the SERPING1 gene, which results in deficiency of the blood protein C1-inhibitor (type I HAE) and the F12 gene, which controls Factor XII (type III HAE). There is an additional type in which C1 levels are normal but C1 function is decreased (type II HAE). All three forms are called hereditary angioedema (HAE) or occasionally by the outdated term "hereditary angioneurotic edema" (HANE). In all forms of HAE, swelling may also occur in the digestive tract and other organs. It is life-threatening when it involves the larynx due to the potential for asphyxiation.
In severe cases, stridor of the airway occurs, with gasping or wheezy inspiratory breath sounds and decreasing oxygen levels. Intubation is required in these situations to prevent respiratory arrest and risk of death.
In hereditary angioedema, there is often no direct identifiable cause, although mild trauma, including dental work and other stimuli, can cause attacks. There is usually no associated itch or urticaria, as it is not an allergic response. Patients with HAE can also have recurrent episodes (often called "attacks") of abdominal pain, usually accompanied by intense vomiting, weakness, and in some cases, watery diarrhea, and an unraised, non-itchy splotchy/swirly rash. These stomach attacks can last anywhere from 1-5 days on average, and can require hospitalization for aggressive pain management and hydration. Abdominal attacks have also been known to cause a significant increase in the patient's white blood cell count, usually in the vicinity of 13-30,000. As the symptoms begin to diminish, the white count slowly begins to decrease, returning to normal when the attack subsides. As the symptoms and diagnostic tests are almost indistinguishable from an acute abdomen (e.g. perforated appendicitis) it is possible for undiagnosed HAE patients to undergo laparotomy (operations on the abdomen) or laparoscopy (keyhole surgery) that turns out to have been unnecessary.
HAE may also cause swelling in a variety of other locations, most commonly the limbs, genitals, neck, throat, and face. The pain associated with these swellings varies from mildly uncomfortable to agonizing pain, depending on its location and severity. Predicting where and when the next episode of edema will occur is impossible. Most patients have an average of one episode per month, but there are also patients who have weekly episodes or only one or two episodes per year. The triggers can vary and include infections, minor injuries, mechanical irritation, operations or stress. In most cases, edema develops over a period of 12-36 hours and then subsides within 2-5 days.
The hereditary form (HAE) often goes undetected for a long time, as its symptoms resemble those of more common disorders, such as allergy or intestinal colic. An important clue is the failure of hereditary angioedema to respond to antihistamines or steroids, a characteristic that distinguishes it from allergic reactions. It is particularly difficult to diagnose HAE in patients whose episodes are confined to the gastrointestinal tract. Besides a family history of the disease, only a laboratory analysis can provide final confirmation. In this analysis, it is usually a reduced complement factor C4, rather than the C1-INH deficiency itself, that is detected. The former is used during the reaction cascade in the complement system of immune defense, which is permanently overactive due to the lack of regulation by C1-INH.
Bradykinin plays a critical role in all forms of hereditary angioedema. This peptide is a potent vasodilator, leading to rapid accumulation of fluid in the interstitium. This is most obvious in the face, where the skin has relatively little supporting connective tissue, and edema develops easily. Bradykinin is released by various cell types in response to numerous different stimuli; it is also a pain mediator. Dampening or inhibiting bradykinin has been shown to relieve HAE symptoms.
Various mechanisms that interfere with bradykinin production or degradation can lead to angioedema. ACE inhibitors block ACE, the enzyme that among other actions, degrades bradykinin. In hereditary angioedema, bradykinin formation is caused by continuous activation of the complement system due to a deficiency in one of its prime inhibitors, C1-esterase inhibitor (C1INH), and continuous production of kallikrein, another process inhibited by C1INH. This serine protease inhibitor (serpin) normally inhibits the conversion of C1 to C1r and C1s, which - in turn - activate other proteins of the complement system. Additionally, it inhibits various proteins of the coagulation cascade, although effects of its deficiency on the development of hemorrhage and thrombosis appear to be limited.
There are three types of hereditary angioedema:
Consumption of foods which are themselves vasodilators such as alcohol or cinnamon can increase the probability of an angioedema episode in susceptible patients. If the episode occurs at all after the consumption of these foods, its onset may be delayed overnight or by some hours, making the correlation with their consumption somewhat difficult. In contrast, consumption of bromelain in combination with turmeric may be beneficial in reducing symptoms.
The use of ibuprofen or aspirin may increase the probability of an episode in some patients. The use of acetaminophen typically has a smaller, but still present, increase in the probability of an episode.
As an alternative, drugs known as fibrinolysis inhibitors, such as tranexamic acid, are used, although their effect is comparatively weak and their potential for side effects is questionable.Short-term prophylaxis Short-term prophylaxis is normally administered before surgery or dental treatment. In Germany, C1-INH concentrate is used for this and given 1-11/2 hours before the procedure. In countries where C1-inhibitor concentrate is not available or only available in an emergency (laryngeal edema), high-dose androgen treatment is administered for 5-7 days.Long-term prophylaxis In those with frequent or unpredictable attacks, regular infusions of plasma or inhibitor concentrate may be used. C1-INH concentrate is not available in the US, so sometimes fresh frozen plasma is used. C1inh concentrate is currently under late-stage development for both acute and prophylactic use.New treatment options Clinical development of several new active substances, which intervene in the disease process in different ways, is currently ongoing.
Icatibant (marketed as Firazyr) is a selective bradykinin receptor antagonist, which has been approved in only Europe and not in the USA. After initial borderline results this drug was shown to be effective in phase III trials.
Pharming, a Dutch biotechnology company, is developing a recombinant C1 inhibitor for acute attacks of hereditary angioedema.
No studies have been done on these agents in relation to HAE type III.