Anaphylaxis is often associated with an identifiable trigger, such as a food, medication, or insect sting. Idiopathic anaphylaxis is diagnosed when no specific trigger can be identified after an appropriate evaluation and when conditions, such as mastocytosis and C1 esterase inhibitor deficiency/dysfunction, have been ruled out. (See "Anaphylaxis: Confirming the diagnosis and determining the trigger(s)".)
This topic will review the pathogenesis, diagnosis, treatment, and prognosis of idiopathic anaphylaxis. Other aspects of anaphylaxis are discussed separately. (See "Anaphylaxis: Rapid recognition and treatment" and "Differential diagnosis of anaphylaxis in children and adults".)
Anaphylaxis is defined as a serious allergic reaction that is rapid in onset and may cause death . Symptoms of anaphylaxis involve multiple body organ systems (table 1). (See "Anaphylaxis: Rapid recognition and treatment", section on 'Definition and diagnosis'.)
The diagnosis of anaphylaxis is based upon a detailed description of the acute episode, including antecedent activities and events. The diagnosis of idiopathic anaphylaxis is made when a patient has signs and symptoms consistent with anaphylaxis, but no specific trigger can be identified, and other diseases have been ruled out.
Idiopathic anaphylaxis is more common in adults, although it also occurs in children [2-4]. In several series, up to 70 percent of patients with idiopathic anaphylaxis were female and approximately 50 percent of patients were atopic [2,5,6]. Patients with idiopathic anaphylaxis may also have episodes of anaphylaxis caused by known triggers, such as food, medications, and exercise . The prevalence of idiopathic anaphylaxis in the United States is estimated at approximately 1 in 10,000 .