Persistent urticaria--urticarial reaction caused by late phase reaction?

In ordinary urticaria, individual lesions disappear within 24 hours. We encountered 3 patients who showed urticarial reactions lasting more than 24 hours. In all patients, skin biopsy revealed interstitial dermal edema and a perivascular infiltration predominated by eosinophils, without immunoglobulins or complement deposition, or endothelial fibrinoid degeneration. Their eosinophil counts and serum complement levels were within normal range. No proteinurea or joint pain was observed. They could not be controlled by any medications except for glucocorticoid. These findings indicate our cases are not ordinary urticaria, urticarial reaction accompanied by eosinophilia, urticarial vasculitis or delayed pressure urticaria. We recognize such urticarial reaction as a different clinical entity from the usual urticaria, and we speculate that this condition is caused by late phase reaction because of the clinical course and eosinophil infiltrations.