Causes and Risk Factors of Angioedema

Allergy, environment, and genetics may all play a part

Angioedema is the swelling of the layer of tissue immediately beneath skin called the subcutaneous layer. The condition typically affects the face, tongue, throat, arms, and legs, and may be caused by allergy, a drug reaction, environment, or even stress.

Angioedema can either be acquired (triggered by an allergic reaction) or hereditary (caused by a gene mutation passed through families).

The underlying mechanism of both is a malfunction of the immune system in which chemicals called histamine or bradykinins are abnormally released into the bloodstream.

Acquired Angioedema

Acquired angioedema (AAE) can either be immunologic (related to allergy), non-immunologic (triggered by non-allergic causes), or idiopathic (of unknown origin).

Immunologic Causes

Allergy is the most common cause of angioedema, triggered by a reaction to medications, food, insect stings, or other substances such as latex. The cause is considered immunologic because it involves an abnormal response of the immune system.

For reasons unknown, the body will sometimes mistake an otherwise harmless substance for a dangerous one and disperse large quantities of histamine into the bloodstream as a means of defense.

While histamines are meant to dilate blood vessels so that white blood cells can get closer to the site of an injury, when they are released in the absence of harm, they can trigger an array of adverse symptoms, including hay fever (allergic rhinitis), hives (urticaria), and allergic asthma.

However, unlike any of those reactions, angioedema occurs in subcutaneous tissue just beneath the top layer of skin or mucous membrane. The swelling will neither be itchy nor red and can last for several hours or days. When the swelling finally stops, the skin will usually appear normal with no flaking, peeling, or bruising.

Non-Immunologic Causes

With immunologic angioedema, the cells responsible for instigating the attack are known as mast cells. Mast cells contain granules rich in histamine and, when instructed by the immune system to do so, will undergo a process called degranulation to release histamine into the system.

With non-immunologic angioedema, the immune system has nothing do with the release. Instead, certain chemicals or physiological processes can induce mast cells to degranulate. Reactions will often occur in people with an underlying mast cell disorder, such as mastocytosis.

The drugs commonly associated with this include:

Other non-immunologic causes include blood transfusion, cancers like lymphoma, autoimmune diseases like lupus, and certain infections such as hepatitis, HIV, cytomegalovirus, and Epstein-Barr virus.

Certain physical stimuli such as heat, cold, excessive exercise, vibration, sun exposure, and even emotional stress have been known to cause angioedema.

Idiopathic Angioedema

With idiopathic angioedema, there will no known cause or explanation for the sudden acute swelling. What makes the condition so vexing is that those affected are prone to recurrence, sometimes severe.

According to research from the University of Wisconsin School of Medicine, 55 percent of the 99 people diagnosed with idiopathic angioedema experienced recurrent episodes for more than a year. The face, mouth, and tongue were the areas most commonly affected.

More concerning yet was the fact that 52 percent required at least one visit to the emergency room, while 55 percent reporting receiving at least one course of high-dose corticosteroids to alleviate swelling.

Hereditary Angioedema

Hereditary angioedema (HAE) is considered an autosomal dominant disorder, meaning that you can inherit the problematic gene from just one parent. There are two types of HAE related to mutations in the SERPING1 gene and a third caused by the mutation of the F1 gene.

All three types cause the abnormal activation of the immune system and can cause swelling in all parts of the body. Where HAE differs from AAE is that the main culprit is not histamine. Rather, the attack will be instigated by another naturally occurring compound known as bradykinin.

Bradykinin, like histamine, causes the dilation of blood vessels but does so as a means to regulate body functions. For example, the body will release bradykinins to lower the blood pressure or to regulate respiratory or kidney function.

The abnormal release of bradykinins can trigger angioedema, most often of the legs, arms, genitals, face, lips, larynx, or gastrointestinal (GI) tract. A minor injury or emotional stress can trigger an attack, but most occur without any known cause.

Angioedema of the GI tract can be severe, causing violent vomiting, intense pain, and dehydration from not being able to keep fluids down. If swelling occurs in the throat, it can be life-threatening.

Because ACE inhibitors (used to treat high blood pressure) work by sustaining bradykinin levels, they are among the most common cause of drug-induced angioedema (albeit with a different disease mechanism that opiates or aspirin).

HAE is considered rare, occurring in one of every 50,000 people, and is often only suspected if someone with angioedema does not respond to antihistamines. HAE can usually be confirmed with three blood tests that evaluate the immune response.

Risk Factors

There is really no way to explain why some people get angioedema and others with the same health conditions don't. With that being said, you may be at higher risk if you have or have experienced any of the following:

  • Past drug reactions involving a rash or hives
  • Past allergies involving hives
  • A history of angioedema
  • A family history of hives or angioedema
  • An autoimmune disease such as lupus or Hashimoto's thyroiditis for which angioedema is a possible symptom

If you or a loved one have suffered multiple bouts of angioedema, treatments may be available to prevent future attacks. Options include a nightly dose of the antihistamine Zyrtec (cetirizine) if the cause is allergic or the immune-altering drugs such as Kalbitor (ecallantide) or Firazyr (icatibant).

Source:

Bernstein, J.; Lang, D.; Khan, D. et al. "The diagnosis and management of acute and chronic urticaria: 2014 update." J Allergy Clin Immunol. 2014; 133(5):1270-7.

Inomata, M. "Recent Advances in Drug-Induced Angioedema." Allerg Int. 2012; 61(4):545-57. DOI: 10.2332/alergolint.12-RAI-0493.

Rosenberg, D.; Mathur, S.; and Viswanathan, R. "Clinical Characteristics of Idiopathic Angioedema." J Allergy Clin Immunol. 2017; 139(2):AB235. DOI: 10.1016/j.jaci.2016.12.757.