A 48-year-old woman comes to the office due to a 4-day history of pruritic rash on her legs. The lesions initially worsened rapidly over 1-2 hours, and some lesions resolved by the end of the day. The lesions recurred several times over the past 2-3 days, with each episode lasting 6-8 hours. Temperature is 36.1 C (97 F), blood pressure is 138/77 mm Hg, and pulse is 78/min. Skin examination findings are shown in the image below. The remainder of the physical examination is within normal limits. Which of the following is the most likely diagnosis?

Question

A 48-year-old woman comes to the office due to a 4-day history of pruritic rash on her legs.  The lesions initially worsened rapidly over 1-2 hours, and some lesions resolved by the end of the day.  The lesions recurred several times over the past 2-3 days, with each episode lasting 6-8 hours.  Temperature is 36.1 C (97 F), blood pressure is 138/77 mm Hg, and pulse is 78/min.  Skin examination findings are shown in the image below.  The remainder of the physical examination is within normal limits.  Which of the following is the most likely diagnosis?

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11ec25c8_d394_2137_bc81_fb9450a01bd9_MD0003_00 This patient has acute urticaria, intensely pruritic, well-circumscribed erythematous plaques (ie, wheals) caused by mast cell activation in the superficial dermis. Urticaria lesions can be round or serpiginous and up to several centimeters in diameter. Although individual lesions develop over minutes to hours and resolve within 24 hours, additional lesions may continue to erupt for up to 6 weeks. Angioedema, which is caused by mast cell activation in the deeper dermal and subcutaneous tissues (eg, face, lips, hands, buttocks), sometimes accompanies urticaria. Angioedema Acute urticaria usually represents an IgE-mediated allergic reaction (eg, medications, insect bites, food); additional etiologies include infection (eg, bacterial, viral) and systemic illness (eg, rheumatologic disorder, mastocytosis); many cases are idiopathic. Initial management includes a second-generation H₁ blocker (eg, cetirizine). A single episode typically requires no additional evaluation, although laboratory evaluation and biopsy are recommended for episodes that are unresponsive to therapy or accompanied by systemic symptoms (eg, arthritis). (Choice A) Acute atopic dermatitis presents with erythematous papules and vesicles, not wheals, that are typically distributed over the flexural areas (eg, antecubital fossae) rather than extensor surfaces. Individual lesions persist for days to weeks and are not transient. erythematous papules flexural areas (Choice B) Contact dermatitis is caused by contact with irritants or allergens that acutely cause pruritic, erythematous papules or vesicles that last for days to weeks. Rapid resolution within a day is not typical. papules or vesicles (Choice C) Guttate (drop-like) psoriasis presents with an acute eruption of erythematous papules and 2- to 15-mm plaques with fine scales. Individual lesions are persistent and do not resolve within 24 hours. plaques (Choice D) Pityriasis rosea is a self-limited condition likely caused by a viral etiology. It begins as a solitary herald patch that appears pink on light skin and violet to brown on darker skin. The appearance of this patch is followed by eruption of multiple ovoid papules and plaques with a collarette of scales on the trunk and proximal extremities. Individual lesions usually take 4-6 weeks to resolve. herald patch trunk (Choice F) Viral exanthem is usually associated with fever and other symptoms (eg, cough, diarrhea) of a viral illness. It presents with nonpruritic, erythematous macules and papules that last for days. macules and papules Educational objective: Acute urticaria presents with intensely pruritic, well-circumscribed erythematous plaques (ie, wheals). Individual lesions resolve within 24 hours, but additional lesions may erupt for up to 6 weeks. Angioedema sometimes accompanies urticaria. References: Acute and chronic urticaria: evaluation and treatment. (http://www.ncbi.nlm.nih.gov/pubmed/28671445)

A 48-Year-Old Woman Comes to the Office Due to a 4-Day