Clinical summary and course of idiopathic anaphylaxis in 73 patients.

Seventy-three patients with anaphylaxis of unknown cause were studied. Repeated histories and physical examinations were performed by the Northwestern University (Chicago) allergy service in an attempt to find a cause for the anaphylaxis. Documentation of abnormal physical findings during an episode of anaphylaxis was necessary in each patient. Prior to our initial consultation, these 73 patients had required 115 emergency room visits and 37 hospitalizations. No deaths have occurred in 224 patient years of follow-up from initial presentation. Thirty-eight (52%) patients have infrequent reactions (defined as one episode only or mild episodes less than six times per year) requiring acute treatment alone. Thirty-five (48%) patients have severe or frequent life-threatening reactions (defined as episodes that include syncope, documented hypotension, and airway compromise as major manifestations) requiring maintenance antihistamines and prednisone. Laboratory studies were not helpful in finding a cause of anaphylaxis in any of the 73 patients. Associated atopic conditions were present in 45 patients. Twenty-three patients had chronic idiopathic angioedema, urticaria, or both prior to developing idiopathic anaphylaxis. Sixteen patients only treated acutely for each episode of anaphylaxis and seven patients previously receiving maintenance medication are now asymptomatic without medication for longer than one year.