This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
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 uicarial wheal, confined to the border of the lesion. The most likely diagnosis is 
Select and explain. 
A. Fixed drug eruption, B. Licken planus, C. Uicaria pigmentosa, D. Uicarial vasculitis
C: Uicaria pigmentosa
Answer: C: Uicaria pigmentosa 
Explanation: Uicaria pigmentosa Uicaria is characterized by large, irregularly shaped pruritic, erythematous wheels Special forms of uicaria have special features (Dermographism, cholinergic uicaria, solar uicaria, or cold uritcaria) Most incidents are acute and self-limited over a period of 1-2 weeks Chronic uicaria (episodes lasting> 6 weeks) may have an autoimmune basis The most common immunologic mechanism is hypersensitivity mediated by IgE, seen for most patients with acute uicaria The morphology of the lesions may vary over a period of minutes to hours, resulting in geographic or bizarre, pattern, true uicaria last less than 24 hours and often only 2-4 hours. The most common cause of acute uicaria are foods, viral infections and medications Diagnosis - In vivo allergy skin testing and in vitro RAST testing Determination of serum tryptase (Increased in anaphylaxis, systemic mastocytosis, non IgE mediated disease ("anaphylactoid reaction") ACE inhibitors and Angiotensin II receptors antagonist therapy is contraindicated. Uicaria pigmentosa (mastocytosis) - consists of multiple irregularly shaped hyperpigmented muscle 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