anaphylaxis

anaphylaxis
Field	Emergency medicine, Allergy and immunology

anaphylaxis. It is a severe, life-threatening systemic allergic reaction, typically rapid in onset. The condition is a medical emergency requiring immediate intervention, most commonly with epinephrine. It involves multiple organ systems, including the skin, respiratory tract, cardiovascular system, and gastrointestinal tract.

Signs and symptoms

Initial symptoms often involve the skin, presenting with urticaria, angioedema, pruritus, and flushing. Respiratory compromise is common and may include laryngeal edema, bronchospasm, dyspnea, and stridor. Cardiovascular manifestations can range from tachycardia and hypotension to profound shock, as seen in anaphylactic shock. Gastrointestinal symptoms such as nausea, vomiting, abdominal pain, and diarrhea frequently occur. Neurological symptoms like dizziness, syncope, and a sense of impending doom are also reported. The Ring and Messmer clinical grading scale is sometimes used to classify severity. Symptoms typically begin within minutes to hours after exposure to a trigger.

Causes and risk factors

Common triggers include foods such as peanuts, tree nuts, shellfish, milk, and eggs. Medications like penicillin, non-steroidal anti-inflammatory drugs, and chemotherapy agents are frequent causes. Other triggers encompass Hymenoptera stings from insects like honey bees and yellow jackets, latex, and, rarely, exercise or idiosyncratic factors. Certain medical procedures involving radiocontrast media can induce reactions. Risk factors include a personal history of atopy, such as asthma or eczema, and previous milder allergic reactions. Organizations like the American Academy of Allergy, Asthma & Immunology provide guidelines on risk assessment.

Pathophysiology

The process is primarily an IgE-mediated hypersensitivity reaction, specifically Type I hypersensitivity. Upon re-exposure to an allergen, allergen-specific IgE bound to FcεRI receptors on mast cells and basophils causes cross-linking and cellular activation. This leads to rapid degranulation and release of preformed mediators like histamine, tryptase, and chymase. Newly synthesized mediators, including leukotrienes (e.g., LTC4), prostaglandins (e.g., PGD2), and platelet-activating factor, are also produced. These substances cause vasodilation, increased vascular permeability, bronchoconstriction, and myocardial depression. Some reactions, such as those to radiocontrast media, may occur through non-IgE mediated pathways, often termed anaphylactoid reactions.

Diagnosis

Diagnosis is primarily clinical, based on the acute presentation of symptoms involving multiple organ systems. Criteria established by organizations like the World Allergy Organization are often applied. Measurement of serum tryptase levels, ideally drawn within 15 minutes to 3 hours of symptom onset, can support the diagnosis. Skin prick testing or specific IgE blood tests (e.g., ImmunoCAP) may be used later to identify the causative allergen, but are not for acute diagnosis. Differential diagnoses include severe asthma attacks, vasovagal syncope, systemic mastocytosis, and hereditary angioedema. The National Institute of Allergy and Infectious Diseases funds research into diagnostic biomarkers.

Management

Immediate administration of intramuscular epinephrine into the mid-anterolateral thigh is the first-line and lifesaving treatment. Supportive measures include placing the patient in a supine position, administering supplemental oxygen, and securing airway management if needed. Intravenous fluids such as normal saline or Ringer's lactate are given for hypotension. Secondary medications include H1 antihistamines like diphenhydramine, H2 antihistamines like ranitidine, and corticosteroids such as methylprednisolone, though these do not replace epinephrine. All patients should be observed for a biphasic reaction and provided with an epinephrine autoinjector and an anaphylaxis emergency action plan upon discharge. Guidelines from the American College of Emergency Physicians inform standard protocols.

Epidemiology

Lifetime prevalence is estimated at 0.05–2% in the general population, with rates appearing to increase in many developed countries. It is a leading cause of hospital emergency department visits for acute allergic reactions. Fatalities, while rare, are most often associated with delays in epinephrine administration. Certain populations, such as young adults and those with asthma, are at higher risk. Data from registries like the European Anaphylaxis Registry help track triggers and outcomes. Research supported by the National Institutes of Health continues to investigate demographic trends and risk factors.

Category:Allergology Category:Medical emergencies Category:Immune system disorders