Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 27-year-old woman is evaluated for a 4-week history of wheals, characterized by a burning sensation without pruritus. Each individual lesion persists for 48 hours and slowly resolves, leaving a bruise. Current medications are diphenhydramine, hydroxyzine, cetirizine, and oral contraceptives. The patient’s mother has systemic lupus erythematosus.

On physical examination, vital signs are normal. She has scattered edematous indurated erythematous plaques consistent with wheals. There are scattered ecchymoses at the sites of fading lesions. The patient has no facial lesions or rash, and her mucous membranes are normal. There is no joint swelling or tenderness.

Which of the following is the most appropriate management?

A: Discontinue oral contraceptives
B: Radioallergosorbent testing
C: Skin biopsy
D: Thyroid function testing

MKSAP Answer and Critique

The correct answer is C: Skin biopsy. This item is available to MKSAP 16 subscribers as item 14 in the Dermatology section.

MKSAP 16 released Part A on July 31. More information is available online.

This patient has atypical urticaria, and the diagnostic test of choice is skin biopsy to evaluate for the presence of vasculitis. Her individual lesions last longer than a few hours and are not pruritic. The presence of burning, tingling, or painful wheals is unusual for simple urticaria. Lesions that last for more than 24 hours and resolve with bruising are concerning for urticarial vasculitis. Approximately 50% of patients with urticarial vasculitis have an underlying autoimmune disease such as systemic lupus erythematosus.

Many medications may trigger urticaria. Oral contraceptives can cause urticarial eruptions, including chronic urticaria, typically through progesterone exposure. This frequently manifests as a cyclic urticaria. Urticarial vasculitis is less frequently caused by medications and has not been associated with oral contraceptives.

Patients with a clear food or environmental trigger for urticarial eruptions may benefit from radioallergosorbent (RAST) testing; however, this patient is presenting with atypical urticarial lesions with signs and symptoms concerning for urticarial vasculitis. RAST testing plays no role in the diagnosis of urticarial vasculitis.

Thyroid function testing is indicated in the evaluation of chronic urticaria, in which patients have regular episodes of urticaria over a period of more than 6 weeks. Given the atypical presentation of this patient’s wheals and the lack of historical features or physical examination findings consistent with thyroid disease, testing is not indicated at this time.

Key Point

• Lesions that persist for more than 24 hours and resolve with bruising should be biopsied to evaluate for urticarial vasculitis.

Learn more about ACP’s MKSAP 16.

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