Histopathology of chronic urticaria.

Urticaria of undetermined cause persisting longer than 6 wk is known as chronic idiopathic urticaria (CIU). The differential diagnosis of CIU is lengthy and a skin biopsy may be of value in making a more precise diagnosis. The histopathologic feature that differentiates chronic urticarial lesions from acute urticarial lesions is the presence of a mixed cellular perivascular infiltration, composed mostly of mononuclear cells, surrounding the dermal postcapillary venules. Mast cell numbers in CIU lesions may be increased compared to normal dermis. Various patterns of histopathologic findings have been described in CIU. An understanding of these patterns of infiltrating cells, mediators, cytokines, chemokines and adhesion molecules may provide insight into the mechanism of the cutaneous disease and provide valuable information that will help in the selection of a more effective therapeutic intervention.