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A 32-year-old, well-appearing white man complained of red bumps and redness that had been developing on his skin at sites of pressure for the past 10 months. The patient noted considerable itching and associated discomfort at the affected areas. Individual lesions persisted for approximately one hour after pressure application, but new lesions appeared throughout the day. Oral antihistamines prescribed by his primary-care clinician provided no relief. On examination, several small triangular and linear urticarial papules and plaques were visible on his extremities. When the patient’s back was stroked with the wooden end of a cotton-tipped applicator, a linear wheal appeared quickly. (The photo was taken 10 minutes later.) The patient reported a history of allergy to penicillin.

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