This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Skin
[{'content': "Darrier's sign is seen in - \nSelect and explain. \nA. Darrier's disease, B. Urticaria pigmentosa, C. Allergic vasculitis, D. Atopic dermatitis", 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Urticaria pigmentosao Urticaria pigmentosa is a familial cutaneous disorder characterised by generalised distribution of red brown macules,o Each lesion represents a collection of mast cells in the dermis with hyperpigmentation of overlying epidermis,o The most characteristic features is that these lesions urticate on scratching.o Light scratching with the point of forceps or rounded tip of a pen or even rubbing causes these mast cells to degranulate leading to localized urticaria (become red swollen and enlarged) - Darrier's Sign Extensive release of histamine from mast cell degranulation may result in - Headache, flushing diarrhea and pruritis.", 'role': 'assistant'}]