What is urticaria?

➢ Common disorder mediated by localized mast cell degranulation, which leads to dermal microvascular hyperpermeability. ➢ Resulting erythematous, edematous, and pruritic plaques termed wheals (papules). ➢ Histologic features : usually a sparse superficial perivenular infiltrate of mononuclear cells, rare neutrophils, and sometimes eosinophils. ➢ Superficial dermal edema causes splaying of collagen bundles, making them appear to be more widely spaced than normal. ➢ Degranulation of mast cells, which reside around superficial dermal venules, is difficult to appreciate with routine hematoxylin-eosin (H&E) stains but can be highlighted using a Giemsa stain