Anaphylaxis: a review of 601 cases

The allergist usually sees patients with anaphylaxis after the event for the purposes of identifying the cause, establishing a prognosis, and preventing further episodes. Knowledge of the characteristics of such patients is essential to achieve these goals.

To examine the natural history, clinical manifestations, and factors that affect the patients' adherence to suggested treatment and preventive strategies of anaphylaxis.

A retrospective medical record review spanning 25 years (1978-2003) and follow-up questionnaires were used to obtain data on 601 patients who presented with anaphylaxis of unknown origin to a private university-affiliated allergy-immunology practice.

Patients ranged in age from 1 to 79 years, with a mean age of 37 years. Females comprised 62% of cases. Causes of anaphylaxis were elucidated in 41% of cases. Known causes included foods in 131 patients (22%), medications in 69 cases (11%), and exercise in 31 cases (5%). Two hundred twenty-three patients (37%) were found to be atopic by history confirmed with skin prick testing. The most common manifestation was urticaria and/or angioedema, reported in 87% of patients. Systemic mastocytosis was found in 3 patients. Episodes tended to decline in frequency with time. Adherence to instructions to carry epinephrine can be improved with more effective teaching.

In most cases, the cause of anaphylaxis is undetermined. Women are affected more commonly than men. Systemic mastocytosis should be considered in cases of idiopathic anaphylaxis, and patients with a history of atopy are at an increased risk of developing anaphylaxis. Patients are more reliably carrying epinephrine as a result of changes in physician instructions. Finally, anaphylactic episodes tend to decrease in frequency and severity with time.