<prompt> A 5 year old male child has multiple hyper pigmented macules over the trunk, on rubbing the lesion with the rounded end of a pen. He developed urticarial wheal, confined to the border of the lesion. The most likely diagnosis isFixed drug eruptionLicken planusUrticaria pigmentosaUrticarial vasculitis  <response>: Urticaria is characterized by large, irregularly shaped pruritic, erythematous wheelsSpecial forms of urticaria have special features Dermographism, cholinergic urticaria, solar urticaria, or cold uritcariaMost incidents are acute and self-limited over a period of 1-2 weeksChronic urticaria episodes lasting 6 weeks may have an autoimmune basisThe most common immunologic mechanism is hypersensitivity mediated by IgE, seen for most patients with acute urticariaThe morphology of the lesions may vary over a period of minutes to hours, resulting in geographic or bizarre, pattern, true urticaria last less than 24 hours and often only 2-4 hours.The most common cause of acute urticaria are foods, viral infections and medications Diagnosis - In vivo allergy skin testing and in vitro RAST testingDetermination of serum tryptase Increased in anaphylaxis, systemic mastocytosis, non IgE mediated disease anaphylactoid reactionACE inhibitors and Angiotensin II receptors antagonist therapy is contraindicated.Urticaria pigmentosa mastocytosis - consists of multiple irregularly shaped hyperpigmented macule which may present on the trunk and extremities.Stroking the skin through the lesion with a blunt instrument elicits the classical triple response of Lewis called Dariers signTreatment - Avoides taking drugs of Aspirin, NSAID, drugs, morphine, codeine, procaine, thiamine, polymyxin B and alcohol. .The main stay of treatment is initially includes HI antihistamines Hydroxyzine, cyproheptadine, LoratadineDoxepin TCA - very effective in chronic urticaria.Urticarial vasculitis may be seen as part of serum sickness, associated with fever and arthralgia. 