IgE-mediated anaphylaxic reactions can cause symptoms involving the cutaneous, respiratory, cardiovascular, gastrointestinal, and hematologic system. The onset and manifestations vary according to the route of administration, dose, release of and sensitivity to vasoactive substances, and differing sensitivities of the organs to these substances. These parameters can vary from person to person, and individuals tend to react in a characteristic pattern.
The initial manifestations of anaphylaxis can begin in seconds or take as long as an hour to develop; in severe reactions the onset usually occurs within 5 to 10 minutes of exposure. Initial manifestations often include skin erythema, pruritus, a generalized feeling of warmth and/or impending doom, light-headedness, shortness of breath, nausea, vomiting, or a lump in the throat.
Urticaria is the most common manifestation of anaphylaxis. The rash is generalized and intensely pruritic and consists of well-circumscribed, erythematous, raised wheals with serpiginous borders and blanched centers. Angioedema may accompany urticaria and is typically manifested as swelling of the face, eyes, lips, tongue, pharynx, or extremities. The respiratory tract is commonly involved in fatal anaphylaxis. The early stages of upper airway edema consist of hoarseness, stridor, and/or dysphoria. Angioedema of the epiglottis and larynx can cause mechanical obstruction and death by suffocation. The swelling can extend to the hypopharynx and trachea. Between 25 and 50% of patients dying of anaphylaxis have pathologic changes consistent with severe asthma. Pulmonary hyperinflation, peribronchial congestion, submucosal edema, edema-filled alveoli, and eosinophilic infiltration are noted. The patient experiences shortness of breath, chest tightness, and wheezing. Severe hypoxemia and hypercapnia can occur rapidly.
Cardiovascular collapse is among the most severe clinical manifestations of anaphylaxis. The exact extent of fatal anaphylaxis is unknown inasmuch as anaphylaxis can be associated with myocardial ischemia and ventricular arrhythmias, each of which can cause or be caused by hypotension. Decreased blood pressure may be caused by diffuse peripheral vasodilatation from the release of vasodilatory mediators, decreased effective blood volume secondary to leakage of fluid into tissues, hypoxemia, or primary cardiac dysfunction.
Gastrointestinal manifestations can include nausea, vomiting, cramps, and diarrhea. Central nervous system abnormalities can include delirium and seizures, each of which may be due to hypoxemia and/or hypotension.