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Hereditary angioedema (HAE) and histaminergic angioedema both refer to swelling that occurs under your skin and possibly elsewhere in your body. But they have different causes and often need different treatments.
Getting the right diagnosis can help you and your doctor make a plan for future swelling episodes. Here’s how doctors may tell the difference between HAE and histaminergic angioedema.
At a glance, HAE and histaminergic angioedema might look very similar. But they have different causes and often need different treatments.
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Hereditary angioedema is a rare genetic condition that causes swelling episodes throughout a person’s life because of a genetic mutation (change).
HAE swelling can be sudden and painful. It most often affects the face, hands, feet, and genitals. It can also affect other body parts, including the intestines and airway.
Swelling can move to different areas during a single HAE episode, called an HAE attack. Airway swelling is rare but can be a life-threatening complication if it causes asphyxiation (when you don’t get enough oxygen).
Histaminergic angioedema means swelling caused by the release of histamine and other immune chemicals, often from immune cells called mast cells. It can happen during an allergic reaction, such as a reaction to food, medicine, an insect sting, or latex. But it can also happen for unknown reasons, including with spontaneous hives or angioedema.
Histaminergic angioedema includes both allergic angioedema and spontaneous angioedema.
When no clear allergy trigger is found, doctors may call it spontaneous or idiopathic angioedema.
Histaminergic angioedema can involve swelling in many of the same areas as HAE, including the lips, face, tongue, throat, and hands and feet. It too can be life-threatening if it restricts a person’s breathing or if it comes with a severe allergic reaction called anaphylaxis.
If you visit your doctor for a swelling episode, they’ll ask a series of questions to gather more information. These questions help them differentiate between HAE and histaminergic angioedema and determine which tests you might need.
Your doctor will likely ask about known conditions in your family history that cause swelling. Because HAE is a genetic condition, most people with HAE have immediate family members (like a parent) who have it too. Tell your doctor if any of your family members experience similar swelling episodes.
Allergic reactions affect people with a family history of allergies more than people who don’t have family members with allergies. If you’re aware of allergies in your family, be sure to let your doctor know.
In HAE, attacks happen frequently and can be unpredictable. Before any swelling starts, you might notice early warning signs like a hoarse voice, skin tingling, or fatigue.
Allergic angioedema tends to appear very soon after you come into contact with an allergen, like a food or insect sting. The swelling can happen within minutes of the exposure or can appear up to a couple of hours later. Severe reactions tend to happen rapidly, just seconds or minutes after you come into contact with the allergen.
Spontaneous or idiopathic angioedema can also occur. Usually this angioedema is associated with urticaria (hives) and is unrelated to allergen exposure or HAE.
An HAE attack can last for days at a time. Most swelling in HAE resolves within three to five days. The swelling may be less severe if you take an on-demand medication as soon as you notice warning signs of an attack.
If your angioedema is due to an allergy or arises spontaneously, the swelling usually lasts a day or so. You should let your doctor know if the swelling lasts longer than two or three days, as this may indicate another underlying cause that needs treatment.
Hives and itching can indicate that the swelling comes from the release of histamine due to an allergic reaction or spontaneous hives and angioedema. Hives are itchy welts or spots that appear across your skin. Hives often appear red or pink on lighter skin tones and purple on darker skin tones. Not all allergic angioedema comes with hives.
HAE never causes hives, which sets it apart from other types of angioedema. An HAE attack can sometimes involve a rash, but the rash isn’t itchy.
Gastrointestinal (GI) symptoms like abdominal pain, vomiting, and diarrhea can accompany HAE swelling if the HAE attack also causes swelling in your GI tract. Severe allergic reactions can also cause similar symptoms.
However, in allergic reactions, the GI symptoms tend to occur along with other signs of anaphylaxis. In HAE, the GI symptoms are often the only sign of swelling during the attack.
Don’t forget to tell your doctor about GI symptoms, even if they seem unrelated to your angioedema at first.
HAE swelling can occur with or without a trigger. In some HAE attacks, there is a clear trigger that leads to symptoms. Not all triggers are clear, but some of the most common triggers of HAE swelling are:
Histaminergic angioedema can be triggered by something that you are allergic to (certain foods, insect stings, medications), or it can be triggered by stress, illness, heat, or cold.
HAE episodes can happen repeatedly — and often unpredictably — throughout a person’s life. In one study, the median number of HAE attacks per month was six, but people can experience them more or less frequently. Attacks often become more frequent after puberty.
Histaminergic angioedema can occur due to an exposure to an allergen or can be spontaneous. Allergic angioedema can occur any time you’re exposed to your allergen. If you know you have an allergy, it’s important to avoid your allergen to the best of your ability.
After your doctor asks questions about your angioedema, they can use additional tests to confirm a diagnosis of HAE, histaminergic angioedema, or another cause of swelling. They’ll recommend tests based on your answers to their questions.
Most cases of HAE can be diagnosed with blood tests that measure the level and function of C1 inhibitor (C1INH). C1INH is a protein that helps control swelling in the body.
Your doctor may also use blood tests to check your levels of another related protein called C4. In some people with HAE, C1INH and C4 test results can be normal. This is called HAE with normal C1 inhibitor.
If your symptoms still seem like HAE, your doctor may recommend genetic testing or refer you to a specialist.
If your doctor thinks your angioedema is related to an allergy, they can use allergy skin tests or allergy blood tests to help confirm the diagnosis.
Doctors may explore other possible causes of swelling if they can’t narrow it down to HAE, histaminergic angioedema, or an allergy. For example, ACE inhibitors can cause angioedema in some people.
Confirming your diagnosis can help you manage your condition and take the right actions in the event of emergency throat swelling. Treatments that work for histaminergic angioedema, such as antihistamines, corticosteroids, and emergency epinephrine, won’t help with swelling from an HAE attack.
Conversely, HAE treatments won’t help with histaminergic angioedema, whether it’s allergic or spontaneous. Your doctor may prescribe HAE-specific on-demand medications to use as soon as swelling occurs, or they may prescribe preventive medications to prevent future HAE attacks.
When triggers are known, avoiding them may reduce swelling episodes. But some people with histaminergic angioedema never find a clear trigger. Your doctor can still help you find a treatment plan to reduce future episodes.
On myHAEteam, people share their experiences with hereditary angioedema, get advice, and find support from others who understand.
Can you think of any other differences between hereditary angioedema and histaminergic angioedema? Let others know in the comments below.
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