Anaphylaxis

Definition

Anaphylaxis is a rapidly progressing, life-threatening allergic reaction.

Description

Anaphylaxis is a type of allergic reaction, in which the immune system responds to otherwise harmless substances from the environment. Unlike other allergic reactions, however, anaphylaxis can kill. Reaction may begin within minutes or even seconds of exposure, and rapidly progress to cause airway constriction, skin and intestinal irritation, and altered heart rhythms. In severe cases, it can result in complete airway obstruction, shock, and death.

Causes and symptoms

Causes

Like the majority of other allergic reactions, anaphylaxis is caused by the release of histamine and other chemicals from mast cells. Mast cells are a type of white blood cell and they are found in large numbers in the tissues that regulate exchange with the environment: the airways, digestive system, and skin.

On their surfaces, mast cells display antibodies called IgE (immunoglobulin type E). These antibodies are designed to detect environmental substances to which the immune system is sensitive. Substances from a genuinely threatening source, such as bacteria or viruses, are called antigens. A substance that most people tolerate well, but to which others have an allergic response, is called an allergen. When IgE antibodies bind with allergens, they cause the mast cell to release histamine and other chemicals, which spill out onto neighboring cells.

The interaction of these chemicals with receptors on the surface of blood vessels causes the vessels to leak fluid into surrounding tissues, causing fluid accumulation, redness, and swelling. On the smooth muscle cells of the airways and digestive system, they cause constriction. On nerve endings, they increase sensitivity and cause itching.

In anaphylaxis, the dramatic response is due both to extreme hypersensivity to the allergen and its usually systemic distribution. Allergens are more likely to cause anaphylaxis if they are introduced directly into the circulatory system by injection. However, exposure by ingestion, inhalation, or skin contact can also cause anaphylaxis. In some cases, anaphylaxis may develop over time from less severe allergies.

Anaphylaxis is most often due to allergens in foods, drugs, and insect venom. Specific causes include:

• Fish, shellfish, and mollusks
• Nuts and seeds
• Stings of bees, wasps, or hornets
• Papain from meat tenderizers
• Vaccines, including flu and measles vaccines
• Penicillin
• Cephalosporins
• Streptomycin
• Gamma globulin
• Insulin
• Hormones (ACTH, thyroid-stimulating hormone)
• Aspirin and other NSAIDs
• Latex, from exam gloves or condoms, for example.

Exposure to cold or exercise can trigger anaphylaxis in some individuals.

KEY TERMS

ACTH— Adrenocorticotropic hormone, a hormone normally produced by the pituitary gland, sometimes taken as a treatment for arthritis and other disorders.

Antibody— An immune system protein which binds to a substance from the environment.

NSAIDs— Non-steroidal antiinflammatory drugs, including aspirin and ibuprofen.

Tracheostomy tube— A tube which is inserted into an incision in the trachea (tracheostomy) to relieve upper airway obstruction.

Symptoms

Symptoms may include:

• Urticaria (hives )
• Swelling and irritation of the tongue or mouth
• Swelling of the sinuses
• Difficulty breathing
• Wheezing
• Cramping, vomiting, or diarrhea
• Anxiety or confusion
• Strong, very rapid heartbeat (palpitations )
• Loss of consciousness.

Not all symptoms may be present.

Diagnosis

Anaphylaxis is diagnosed based on the rapid development of symptoms in response to a suspect allergen. Identification of the culprit may be done with RAST testing, a blood test that identifies IgE reactions to specific allergens. Skin testing may be done for less severe anaphylactic reactions.

Treatment

Emergency treatment of anaphylaxis involves injection of adrenaline (epinephrine) which constricts blood vessels and counteracts the effects of histamine. Oxygen may be given, as well as intravenous replacement fluids. Antihistamines may be used for skin rash, and aminophylline for bronchial constriction. If the upper airway is obstructed, placement of a breathing tube or tracheostomy tube may be needed.

Prognosis

The rapidity of symptom development is an indication of the likely severity of reaction: the faster symptoms develop, the more severe the ultimate reaction. Prompt emergency medical attention and close monitoring reduces the likelihood of death. Nonetheless, death is possible from severe anaphylaxis. For most people who receive rapid treatment, recovery is complete.

Prevention

Avoidance of the allergic trigger is the only reliable method of preventing anaphylaxis. For insect allergies, this requires recognizing likely nest sites. Preventing food allergies requires knowledge of the prepared foods or dishes in which the allergen is likely to occur, and careful questioning about ingredients when dining out. Use of a Medic-Alert tag detailing drug allergies is vital to prevent inadvertent administration during a medical emergency.

People prone to anaphylaxis should carry an "Epi-pen" or "Ana-kit," which contain an adrenaline dose ready for injection.

Resources

OTHER

The Meck Page. February 20, 1998. 〈http://www.merck.com〉.

Anaphylaxis

Anaphylaxis is a violent allergic reaction of the whole body which can result in death. During anaphylaxis, the allergic person's throat swells so much that she or he cannot breath, while internal organs may start to shutdown. The immune system's attempt to rid the body of a particular substance actually turns against the body itself.

When research on the immune system was progressing in the 1800s, most scientists thought that the body's reactions to invaders were always protective. While researching experimental smallpox innoculations in 1798, Edward Jenner (1749-1823) observed that patients given a second shot often suffered violent reactions. Despite this risk, people were more afraid of the disease than possible inoculation side effects. Jenner's experimentation, which included inoculating subjects with both cowpox and smallpox, eventually led to the development of a successful—and safe—smallpox vaccine.

The first complete study and description of negative immune responses was produced by two Frenchmen, physiologist Charles Richet and physician Paul Portier (1866-1962). During a scientific cruise on the yacht of Prince Albert of Monaco (a small principality on the Mediterranean Sea), Albert suggested that Portier and Richet study the poison (toxin) produced by the tentacles of the Portuguese man-of-war, a jelly-fish. Back in France, the two men continued their studies with extracts of toxin from a sea anemone (a flower-like marine creature). While looking for a toxic dose level, they injected dogs with sea anemone venom. Dogs that survived were given time to recover and then reinjected. Richet expected that the first exposure to the toxin would create a certain amount of immunity in the dogs, the same way that getting a virus gives someone immunity to another encounter with the same disease. Instead, the initial exposure made the dogs hypersensitive. A second, much smaller dose of toxin quickly killed them. Since this result was the opposite of a protective immune response, or prophylaxis, Richet named the hypersensitive reaction anaphylaxis. Richet's identification of anaphylaxis won him the 1913 Nobel Prize for medicine.

After further research, it was discovered that many substances people are allergic to, particularly foods and toxins from animals (such as bee venom), can cause strong reactions. This knowledge provided a valuable warning to physicians engaged in serum (anti-poison) therapy. The researchers began checking patients for possible sensitization before injecting potentially toxic amounts of serum. Those patients with an initially severe reaction to an allergen (or allergy-causing agent) were advised to carry epinephrine (an artificial hormone) to inject immediately if they had a severe reaction.

[See also Hormone ]

Anaphylaxis

Anaphylaxis is a severe allergic reaction. The symptoms appear rapidly and can be life threatening.

The symptoms of anaphylaxis include the increased output of fluid from mucous membranes (e.g., passages lining the nose, mouth, and throat), skin rash (e.g., hives), itching of the eyes, gastrointestinal cramping, and stiffening of the muscles lining the throat and trachea. As a result of the latter, breathing can become difficult. These symptoms do not appear in every case. However, some sort of skin reaction is nearly always evident.

Anaphylaxis results from the exposure to an antigen with which the individual has had previous contact, and has developed a heightened sensitivity to the antigen. Such an antigen is also known as an allergen. The allergen binds to the specific immune cell (e.g., immunoglobulin E, also known as IgE) that was formed in response to the initial antigen exposure. IgE is also associated with other specific cells of the immune system that are called basophils and mast cells. The basophils and mast cells react to the binding of the allergen- IgE complex by releasing compounds that are known as mediators (e.g, histamine , prostaglandin D2, trypase). Release of mediators does not occur when IgE alone binds to the basophils or mast cells.

The release of the mediators triggers the physiological reactions. For example, blood vessels dilate (become larger in diameter) and fluid can pass across the blood vessel wall more easily. Because the immune system is sensitized to the particular allergen, and because of the potent effect of mediators, the development of symptoms can be sudden and severe. A condition called anaphylactic shock can ensue, in which the body's physiology is so altered that failure of functions such as the circulatory system and breathing can occur. For example, in those who are susceptible, a bee sting, administration of a penicillin-type of antibiotic, or the ingestion of peanuts can trigger symptoms that can be fatal if not addressed immediately. Those who are allergic to bee stings often carry medication with them on hikes.

Anaphylaxis occurs with equal frequency in males and females. No racial predisposition towards anaphylaxis is known. The exact number of cases is unknown, because many cases of anaphylaxis are mistaken for other conditions (e.g., food poisoning). However, at least 100 people die annually in the United States from anaphylactic shock.

See also Allergies; Immunoglobulins and immunoglobulin deficiency syndromes

anaphylaxis , hypersensitive state that may develop after introduction of a foreign protein or other antigen into the body tissues. When an anaphylactic state exists, a second dose of the same protein (commonly an antibiotic such as penicillin, or certain insect venoms) will cause a violent allergic reaction. Anaphylaxis results from the production of specific antibodies in the tissues in very high concentration; the violent reaction is produced by the neutralization of antigens by the antibodies. The histamines released during the reaction are thought to cause the most damage, i.e., severe vasodilation and loss of capillary fluid, resulting in circulatory collapse. Other symptoms include urticaria or edema, choking, coughing, shock, and loss of consciousness. Death may occur within 5 to 10 min if no medical help is available. Anaphylaxis differs from immunity ; in immunity, antibodies circulate in the blood and neutralize antigens without producing a violent reaction. See also allergy ; serum sickness .

anaphylaxis (ană-fil-aks-iss) n. an emergency condition resulting from an abnormal and immediate allergic response to a substance to which the body has become intensely sensitized. It results in flushing, itching, nausea and vomiting, swelling of the mouth and tongue and airway enough to often cause obstruction, wheezing, a sudden drop in blood pressure, and even sudden death. In this extreme form it is called anaphylactic shock. Treatment, which must be given immediately, consists of adrenaline (epinephrine) injection, oxygen with possible advanced support of the airway, intravenous fluids, intravenous corticosteroids, and antihistamines.
—anaphylactic adj.

anaphylaxis An abnormal immune response that occurs when an individual previously exposed to a particular antigen is re-exposed to the same antigen. Anaphylaxis may follow an insect bite or the injection of a drug (such as penicillin). It is caused by the release of histamine and similar substances and may produce a localized reaction or a more generalized and severe one, with difficulty in breathing, pallor, or drop in blood pressure, unconsciousness, and possibly heart failure and death. See also allergy.

an·a·phy·lax·is / ˌanəfəˈlaksis/ • n. (also an·a·phy·lac·tic shock / -ˈlaktik/ ) Med. an extreme, often life-threatening, allergic reaction to an antigen (e.g., a bee sting) to which the body has become hypersensitive following an earlier exposure. DERIVATIVES: an·a·phy·lac·tic / -ˈlaktik/ adj.

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