Exercise-induced anaphylactic syndromes. Insights into diagnostic and pathophysiologic features.

To differentiate the diagnoses of exercise-induced anaphylaxis and cholinergic urticaria/anaphylaxis, we developed reproducible diagnostic provocative challenges. The data derived from the study of two representative patients, one with cholinergic urticaria and the other with exercise-induced anaphylaxis, suggest approaches to distinguishing these diagnoses. After specific exercise challenges, both patients developed symptoms consistent with anaphylaxis and had associated increases in plasma histamine levels. After passive heat challenges inducing increases in core body temperature more than 0.7 degrees C, only the patient with cholinergic urticaria developed anaphylactic symptoms and had a rise in the plasma histamine level. Neither patient developed symptoms of anaphylaxis when core body temperatures were increased after administration of intravenous endotoxin. Thus, passive heat challenges are extremely valuable in differentiating these two exercise-related syndromes. Although not important in exercise-induced anaphylaxis, specific thermoregulatory mechanisms appear to play an intricate part in the pathophysiology of cholinergic urticaria/anaphylaxis.