Anaphylaxis: a review of 601 cases.

BACKGROUND: 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.

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

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.