History and exam
Key diagnostic factors
common
acute onset
Onset is within minutes to a maximum of 1 hour after exposure.
May follow a uniphasic course, with resolution of symptoms within hours of treatment and without symptom recurrence on repeated exposure to the trigger. In about 5% to 20%, episodes are described to follow a biphasic course, with symptom recurrence after resolution of the initial presentation.[15]
urticaria
Commonly known as hives. A common symptom characterized by blanching, raised, palpable wheals, which can be linear, annular (circular), or arcuate (serpiginous). Occur on any skin area and are usually transient and migratory.
angioedema
A manifestation of immediate hypersensitivity with a circumscribed swelling of any part of the body. Immediate treatment is warranted if it involves the airways.
flushing
A frequent sign of anaphylaxis due to vasodilation.
Has to be distinguished from other causes such as carcinoid syndrome, postmenopause, chlorpropamide, alcohol, idiopathic flush, medullary carcinoma of the thyroid, and related to autonomic epilepsy.
dyspnea
May be caused by upper airway obstruction or increased resistance to air movement due to lower airway bronchoconstriction in response to allergen exposure.
wheezing
Most often due to reactive airway disease. Wheezing, in conjunction with an overinflated chest, the use of accessory muscles, and preference for the forward-leaning position, points to bronchoconstriction and requires immediate treatment with bronchodilators. A peak flow meter will indicate a reduction of the forced expiratory volume.
rhinitis
Together with bilateral conjunctivitis, is often an early sign of progressive respiratory involvement.
Other diagnostic factors
common
allergen ingestion
Can be caused by ingestion, but also by handling and inhalation of the food aerosol.
Prevalence is greatest in the pediatric population and decreases with age.[23]
Mostly peanuts, tree nuts, fish, and shellfish are responsible. Eating habits of a population influence the type of food causing the allergic reaction (e.g., peanut allergy in the US and sesame allergy in children in Israel).
Many patients are unaware of their food allergy and may be unaware the meal includes the allergen.
In North America, Europe, and Australia, food-induced anaphylaxis is thought to account for one third to one half of anaphylaxis cases presenting to emergency departments.[17]
insect stings or bites
A common cause around the world. Insect stings with the ubiquitous Hymenoptera (wasps and bees) are commonplace globally, while ant stings and spider bites are limited to their geographic prevalence.[25]
pruritus
Together with rash, is an early sign of urticaria.
inspiratory stridor and hoarse voice
bilateral conjunctivitis
As a result of allergen exposure, redness, excessive tearing, sensitivity to light, a feeling of grittiness, swelling of the eyelids, and itchiness may occur.
Both eyes are usually affected simultaneously. Together with rhinitis, is often an early sign of progressive respiratory involvement.
nausea and vomiting
Suggests the ingestion of an allergen and may be associated with other gastrointestinal symptoms, such as abdominal cramps or diarrhea.
abdominal cramping or pain
Often painful; points to a food allergen, and may be associated with other gastrointestinal symptoms, such as nausea and vomiting or diarrhea.
agitation/anxiety
Anaphylaxis may present with a complex combination of emotions that include fear, apprehension, worry, and disorientation. These may be accompanied by physical sensations such as heart palpitations, nausea, chest pain, or shortness of breath. These neuropsychological symptoms of anaphylaxis may be worsened by hypotension, and may even be triggered by administration of epinephrine (adrenaline), but tend to resolve as the other allergic symptoms abate.
confusion/disorientation
Refers to loss of orientation by time, location, and personal identity, and often loss of memory. Confusion/disorientation may be worsened by hypotension, and may be triggered by administration of epinephrine (adrenaline), but tends to resolve as the other allergic symptoms abate.
tachycardia
Often associated with hypotension and may herald cardiovascular collapse. The pulse may be so weak that heartbeats may be missed on radial palpation. May lead to underestimation of the cardiac frequency and hence the severity of the patient's condition. The true heart rate is best documented on an ECG monitor.
dizziness
Common descriptions include words such as light-headed, floating, woozy, giddy, confused, helpless, or fuzzy. Presyncope is the medical term. Anaphylaxis can lead to dizziness and eventually to syncope due to the hypotension associated with the intravascular fluid shifts to the third space, mediated by vasoactive substances released from mast cells and basophils.
syncope
Characterized by temporary loss of consciousness and posture, described as fainting or passing out. Usually related to temporary insufficient blood flow to the brain. Anaphylaxis can lead to syncope due to the hypotension associated with the intravascular fluid shifts to the third space, mediated by vasoactive substances released from mast cells and basophils.
sense of impending doom (angor animi)
Describes a person's perception that they are in fact dying. Although it may be more typical for patients suffering from acute coronary syndrome such as angina, the inspiratory stridor, the dyspnea, and the faint feeling and dizziness secondary to hypotension compound the psychological stress of severe allergic reactions.
uncommon
recent exercise
Exercise-induced anaphylaxis is triggered by physical activity and typically occurs 2 to 4 hours after allergen ingestion.[17] Initial symptoms include diffuse warmth, pruritus, erythema, and urticaria. Progression to angioedema, gastrointestinal symptoms, fatigue, laryngeal edema, and/or vascular collapse is common.
Factors associated with this type of anaphylaxis include medications (e.g., aspirin or other nonsteroidal anti-inflammatory drugs [NSAIDs]) and food ingestion (wheat, shellfish, and celery, among others) before or after the exercise. Therefore, in predisposed individuals, exercise should be avoided in the immediate postprandial period. A higher rate of atopy has been described.
hot or cold exposure
hypotension
Vasodilation leads to a relative hypovolemia and severe hypotension, the cardinal clinical feature of anaphylaxis.[51] Increased capillary permeability causes fluid loss to the extravascular space, thus compounding hypotension.
bradycardia
Sometimes secondary to concomitant cardiac medications, such as beta-blockers. Sudden positional change should be avoided in these patients, as this may lead to collapse.[50]
cardiac arrest
The abrupt cessation of normal circulation or the absence of effective perfusion of vital organs. Diagnosed by absent pulses. The patient will be unresponsive and stop breathing, and the skin will appear dusky.
diarrhea
May accompany other symptoms of the gastrointestinal system, such as nausea and vomiting and abdominal pain, after allergen ingestion.
visual disturbances
Rare, caused by anaphylactic shock secondary to isolated ischemia of both lateral geniculate bodies. In several cases, the allergen was an antibiotic. Visual field losses occurred, but resolved within 7 weeks.[65]
tremor
Both endogenous catecholamines and epinephrine (adrenaline) administered by first responders may cause tremor and nervousness.
seizures
Neurological manifestations, although uncommon, may include seizures.
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