Idiopathic anaphylaxis: a series of 335 cases

Idiopathic anaphylaxis is anaphylaxis with no definable etiology and no trigger by exogenous allergens. Initially described in 1978, idiopathic anaphylaxis has been subsequently characterized and treatment protocols have been established.

The demographics and course of 335 patients (225 previously reported) treated with prednisone, hydroxyzine, and albuterol are now reported.

Ages ranged from 5 to 83 years. There were nine new pediatric patients in this series totaling 14 (4.2%). Atopy was common (48%) with 34 new patients with asthma. The duration of symptoms prior to presentation ranged from three days to 27 years. One hundred thirty-two patients with idiopathic anaphylaxis were available for follow-up. Twenty of these are currently receiving prednisone for control of idiopathic anaphylaxis, seven of them as part of their initial therapy, and ten for control of recurrence of symptoms. Three patients required continuous alternate day prednisone for control of symptoms (corticosteroid-dependent idiopathic anaphylaxis). Of the 335 patients, there were no longer any patients with the diagnosis of malignant idiopathic anaphylaxis defined as requiring prednisone, 20 mg daily, or 60 mg every other day, for control of idiopathic anaphylaxis. Of the six patients previously diagnosed with malignant idiopathic anaphylaxis, five no longer required prednisone and one has a decreased prednisone requirement of 20 mg on alternate days. Hospital visits were significantly reduced by the management regimens. There were no fatalities from idiopathic anaphylaxis in this series.

The incidence of idiopathic anaphylaxis is increasing in our practice with more patients being evaluated each year. During 1104 patient years of observation (the longest period of single patient observation being 24 years), no inciting agent has been found responsible for the anaphylactic symptoms. Prognosis continues to remain good with the majority of patients achieving remission with pharmacotherapy.