Angioedema is an area of swelling (edema) of the lower layer of skin and tissue just under the skin or mucous membranes. The swelling may occur in the face, tongue, larynx, abdomen, or arms and legs.

Often it is associated with hives, which are swelling within the upper skin. Onset is typically over minutes to hours.

The underlying mechanism typically involves histamine or bradykinin. The version related to histamine is due to an allergic reaction to agents such as insect bites, foods, or medications. The version related to bradykinin may occur due to an inherited problem known as C1 esterase inhibitor deficiency, medications known as angiotensin-converting enzyme inhibitors, or a lymphoproliferative disorder.

Treatment to protect the airway may include intubation or cricothyroidotomy. Histamine-related angioedema can be treated with antihistamines, corticosteroids, and epinephrine. In those with bradykinin-related disease a C1 esterase inhibitor, ecallantide, or icatibant may be used. Fresh frozen plasma may be used instead. In the United States the disease affects about 100,000 people a year.

The skin of the face, normally around the mouth, and the mucosa of the mouth and/or throat, as well as the tongue, swell over the period of minutes to hours. The swelling can also occur elsewhere, typically in the hands. The swelling can be itchy or painful. There may also be slightly decreased sensation in the affected areas due to compression of the nerves. Urticaria (hives) may develop simultaneously.

In severe cases, stridor of the airway occurs, with gasping or wheezy inspiratory breath sounds and decreasing oxygen levels. Tracheal intubation is required in these situations to prevent respiratory arrest and risk of death.

Sometimes, the cause is recent exposure to an allergen (e.g. peanuts), but more often it is either idiopathic (unknown) or only weakly correlated to allergen exposure.

In hereditary angioedema (HAE), often no direct cause is identifiable, 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, nonitchy splotchy/swirly rash. These stomach attacks can last one to five 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 13,000 to 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.

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