Exercise-induced urticaria and anaphylaxis.

Five patients with exercise-induced anaphylactoid reactions are reported. Because of a growing interest in physical exercise and the severity of the symptoms it is important to recognize this condition, even though rare. All of our 5 patients had a history of urticaria and anaphylaxis in association with physical stress, but it seems difficult to induce anaphylactoid reactions under laboratory conditions. Two different clinical patterns could be distinguished in these patients. Three had the anaphylactoid form with signs of alternative complement pathway activation, while 2 patients had the variant form presenting first as cholinergic urticaria and progressing to angioedema and vascular collapse. The latter patients had elevated plasma histamine levels during challenge, but no sign of complement activation was observed. Our findings suggest differing pathomechanisms for these two forms.