A 41-year-old woman comes to the office due to a pruritic rash on her legs for the past 2 weeks. The rash started after she returned from a hiking trip. The patient lives with her husband, who does not have a similar rash. She has no medical conditions and takes no medications. Vital signs are normal. Skin examination findings are shown in the exhibit. Which of the following is the most likely diagnosis of this patient's condition?

Question

A 41-year-old woman comes to the office due to a pruritic rash on her legs for the past 2 weeks.  The rash started after she returned from a hiking trip.  The patient lives with her husband, who does not have a similar rash.  She has no medical conditions and takes no medications.  Vital signs are normal.  Skin examination findings are shown in the exhibit.  Which of the following is the most likely diagnosis of this patient's condition?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c12a_7bf6_8f63_733607d878b2_MD0005_00 This patient has papular urticaria, likely caused by insect bites (eg, ticks, mites) acquired during her hiking trip. Contrary to the name, papular urticaria is a delayed hypersensitivity reaction to insect bites and is not true urticaria. Unlike the more common local reaction caused by irritants in insect saliva, which generally is immediate and resolves within a few hours, papular urticaria may have a delayed onset and a prolonged and sometimes recurrent course over weeks to months. Papular urticaria can occur at any age but is more common in children than in adults, likely due to desensitization with age. Papular urticaria presents as 0.5- to 1-cm erythematous and pruritic papules on exposed skin, most commonly on the legs. Lesions may be surrounded by pale halos due to dermal edema. Because papular urticaria is a hypersensitivity reaction, household contacts typically do not have a similar rash. Treatment includes second-generation (ie, nonsedating) H₁ blockers (eg, cetirizine) to alleviate severe pruritus and topical corticosteroids applied to individual lesions. In addition, patients with ongoing exposure should be isolated from the source of the bites (eg, use insect repellent, treat pet flea infestation). Spontaneous resolution is expected within months. pale halos (Choice A) Guttate (drop-like) psoriasis presents with an acute eruption of erythematous papules and small plaques with fine scales, findings absent in this patient. plaques (Choice B) Lichen planus is a chronic inflammatory condition that presents with pruritic, purple/pink, polygonal papules and plaques. Acute onset and halos around lesions are not characteristic. Lichen planus (Choice C) Nummular eczema is a pruritic eruption of 1- to 10-cm coin-shaped (nummular) eczematous patches typically involving the extremities. Subcentimeter papules are not characteristic. Nummular eczema (Choice E) Pityriasis rosea begins as a solitary herald patch that appears pink or peach on light skin and violet to brown on darker skin. The appearance of this patch is followed by eruption of multiple pruritic, ovoid papules and plaques with a collarette of scales on the trunk and proximal extremities. Involvement limited to the distal legs is atypical. herald patch trunk Educational objective: Papular urticaria is a delayed hypersensitivity reaction to insect bites that results in prolonged and recurrent pruritic papules on exposed skin. Treatment includes second-generation H₁ blockers and topical corticosteroids. Spontaneous resolution is expected within months. References: Papular urticaria. (http://www.ncbi.nlm.nih.gov/pubmed/11534921)

A 41-Year-Old Woman Comes to the Office Due to a Pruritic