Anaphylaxis

Anaphylaxis is a life-threatening allergic reaction that necessitates immediate medical intervention. It manifests rapidly, often within minutes to hours, and involves multiple organ systems. This condition requires urgent treatment, even if initial symptoms seem to subside following the administration of emergency medication.

Signs and Symptoms

Anaphylaxis typically presents with a variety of symptoms across different organ systems. Commonly affected areas include the skin, respiratory system, gastrointestinal tract, cardiovascular system, and central nervous system. The following are some of the key manifestations:

Skin

Symptoms usually include generalised hives, itchiness, flushing, or swelling (angioedema) of the affected tissues. A burning sensation rather than itchiness may be described by those with angioedema. Swelling of the tongue or throat, which occurs in about 20% of cases, can obstruct the airway. Additionally, a runny nose and swelling of the conjunctiva may be observed.

Respiratory

Respiratory symptoms include shortness of breath, wheezes, or stridor. Wheezing is typically due to bronchial muscle spasms, while stridor is related to upper airway obstruction caused by swelling. Other symptoms can include hoarseness, pain with swallowing, or a cough.

Cardiovascular

Cardiovascular signs may include a rapid heart rate resulting from low blood pressure, though in 10% of cases, a slow heart rate can occur. Severe hypotension or shock may lead to lightheadedness or loss of consciousness. Rarely, very low blood pressure might be the only symptom.

Other

Gastrointestinal symptoms such as severe abdominal pain and vomiting can occur. Neurological signs may include confusion or feelings of anxiety. A severe sense of impending doom is often reported.

Causes

Anaphylaxis can be triggered by various factors including insect bites, foods, and medications. Foods are the most common cause in children and young adults, while medications and insect stings are more common in older adults. Other triggers can include exercise, temperature changes, and even certain vaccinations.

Mechanism

The pathophysiology of anaphylaxis involves the rapid release of inflammatory mediators from mast cells and basophils, usually triggered by immunologic mechanisms involving IgE antibodies. Non-immunologic mechanisms can also cause mast cell degranulation via direct interactions, such as with contrast media or temperature changes.

Diagnosis

Diagnosis is primarily based on clinical presentation. Key indicators include skin or mucosal involvement plus respiratory difficulty or hypotension, or two or more of the following symptoms after exposure to an allergen: skin or mucosal involvement, respiratory difficulties, hypotension, or gastrointestinal symptoms. Blood tests for tryptase or histamine might help confirm the diagnosis in some cases.

Treatment

Epinephrine

The primary treatment for anaphylaxis is the administration of epinephrine (adrenaline) intramuscularly into the mid-outer thigh. This may be repeated every 5 to 15 minutes if the response is insufficient. Epinephrine autoinjectors, such as the EpiPen, are commonly used for self-administration.

Adjuncts

Adjunctive treatments may include antihistamines and corticosteroids, though their efficacy in acute management is less clear. Intravenous fluids and supplemental oxygen are often necessary, and patients should be observed in a medical setting for potential biphasic reactions.

Prognosis and Epidemiology

With prompt treatment, the prognosis for anaphylaxis is generally good. Mortality rates range from 0.7% to 20%, depending on the cause and rapidity of treatment. Anaphylaxis affects approximately 4–100 per 100,000 persons per year, with a lifetime risk of 0.05–2%. The incidence has been increasing, particularly with food-related causes.

History

The phenomenon of anaphylaxis was first described by French physiologists Charles Richet and Paul Portier in 1902. They coined the term from Greek words meaning "against protection" and Richet was awarded the Nobel Prize in 1913 for his work on this condition.

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Self-assessment MCQs (single best answer)

What is the primary treatment for anaphylaxis?

Which of the following symptoms is typically related to the respiratory system in anaphylaxis?

Which age group is most commonly affected by food-induced anaphylaxis?

What is the typical mechanism that causes mast cell degranulation in anaphylaxis?

What is the name of the condition characterised by swelling of the tissues, often described as a burning sensation rather than itchiness?

Which test might help confirm the diagnosis of anaphylaxis by measuring levels of certain substances in the blood?

What is the typical observation period in a medical setting after an anaphylactic reaction to monitor for biphasic reactions?

What is the lifetime risk of experiencing anaphylaxis?

Who first described the phenomenon of anaphylaxis and won a Nobel Prize for this work?

Which symptom might indicate anaphylaxis involvement of the cardiovascular system?