Kristina Wilson, MD, MPH, FAAP, CAQSM
The causative agent in anaphylaxis remains unknown in up to 1/3 of cases.
Food is the most common causative agent (about 1/3 of known cases) in children.
Pharmacotherapeutic agents are the most common cause in adults.
Other common causes include Hymenoptera stings and latex.
Key to management and treatment is early recognition and immediate initiation of appropriate medical therapy.
Epinephrine is the undisputed initial therapy for anaphylaxis, and its administration should never be delayed.
Failure to inject epinephrine promptly has been identified as the most important factor contributing to death in patients experiencing anaphylaxis.
Severe, potentially life-threatening systemic hypersensitivity reaction
Allergic type mediated by immunoglobulin E (IgE):
Involves the respiratory and/or cardiovascular systems
Patients may have a history of less severe reaction previously on exposure to relevant allergen.
Exercise-induced anaphylaxis (EIAn):
Occurs in response to physical exertion
Subset of patients must have associated food trigger—food-dependent exercise-induced anaphylaxis (FDEIAn).
Reproducible, rapid onset of erythema, pruritus, and edema after exposure to cold
Occasionally involves abnormal circulating proteins (i.e., cryoglobulins or cryofibrinogens); agglutinates or precipitates at lower temperatures
Death rates from the most common causes of anaphylaxis have varied:
Food induced has increased.
Insect sting has declined.
Drug induced has increased.
8 to 50/100,000 person-years in Western countries
Incidence rates vary widely owing to differences in sample populations, data-collection methods, and varying definitions of anaphylaxis.
Lifetime prevalence of 0.05-2.0% in Western countries (1), rising especially in children
ETIOLOGY AND PATHOPHYSIOLOGY
Nonallergic: direct basophil/mast cell-mediated:
Prior anaphylaxis event can predict subsequent anaphylaxis:
As the only risk factor, prior anaphylaxis has a poor ability to identify patients who might develop anaphylaxis.
14% of anaphylaxis admissions for peanut sensitivity have a prior history of anaphylaxis.
Often occurs following a previous mild allergic reaction to the same allergen
Most proposed risk factors have limited value owing to a low specificity:
Coexisting atopic disease; especially poorly controlled asthma
Older age at first reaction to food allergy
Clinical risk factors for fatality in anaphylactic reactions (2):
Severe or uncontrolled asthma
Avoidance of known allergen
No available tests exist to predict the likelihood of a person developing anaphylaxis.
Neither size of skin prick test wheal nor the level of serum-specific IgE correlate with reaction severity.
Hymenoptera venom and penicillin: currently available
Oral immunotherapy (OIT) mg doses or sublingual immunotherapy (SLIT) microgram doses over months
Milk, egg, and peanut
20% drop out due to serious side effects such as anaphylaxis
Temporary tolerance maintained with regular ingestion
Permanent immunologic tolerance difficult to demonstrate
Only available in controlled trials
Cold water and air
Cold food and beverages
Promising outlooks: characterization of &bgr;-cell epitope responses:
Specific allergenic epitopes may correlate with severity of reaction.
Individuals have a unique fingerprint of IgE-specific allergenic epitopes, and characterization of this profile may help to determine risk of anaphylaxis.
Diagnosis is made based on clinical symptoms:
Do not underestimate the potential severity of an allergic reaction in its early stages.
Symptoms may progress rapidly.
Suspicion of anaphylaxis requires immediate medical intervention and should not be delayed by diagnostic tests.
Biphasic reactions reported in up to 20% of reactions (3)
Clinical criteria for diagnosing anaphylaxis (3)[C]:
Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (e.g., generalized hives; pruritus or flushing; swollen lips, tongue, and/or uvula) and at least one of the following:
Respiratory compromise (e.g., dyspnea, wheeze/bronchospasm, stridor, reduced peak expiratory flow [PEF], hypoxemia)
Reduced blood pressure (BP) or associated symptoms of end-organ dysfunction (e.g., hypotonia/collapse, syncope, incontinence)
Two or more of the following that occur rapidly after exposure to a likely allergen for that patient:
Involvement of the skin-mucosal tissue (e.g., generalized hives; itch or flush; swollen lips, tongue, and/or uvula)
Respiratory compromise (e.g., dyspnea, wheeze/bronchospasm, stridor, reduce PEF, hypoxemia)
Reduced BP or associated symptoms (e.g., hypotonia/collapse, syncope, incontinence)
Persistent gastrointestinal (GI) symptoms (e.g., crampy abdominal pain, vomiting)
Reduced BP after exposure to known allergen for that patient:
Infants and children: low systolic BP (age specific) or ≥30% decrease in systolic BP
Adults: systolic BP of < 90 mm Hg or > 30% decrease from that person’s baseline
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