Do You Recognize This Asymptomatic Lesion?

The parents of an 8-year-old boy seek evaluation of a red patch on their son’s shoulder. The asymptomatic spot erupted 2 weeks earlier. The patient has seasonal allergies and frequently plays with his dog

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What does this look like to you?

A. Psoriasis.
B. Tinea corporis.
C. Impetigo.
D. Contact dermatitis.
E. Erythema migrans.

What is your initial approach?

F. Perform a skin biopsy.
G. Perform a patch test.
H. Perform a potassium hydroxide evaluation.
I. Perform a bacterial culture.
J. Recommend that a veterinarian examine the dog.

Answer: Tinea corporis

A potassium hydroxide evaluation, H, confirmed tinea corporis, B, which responded to a topical antifungal. The family was advised to have their dog examined by a veterinarian, J, since the pet was the suspected source of the dermatophyte.

Erythema migrans associated with Lyme disease was unlikely, since the patient had no prodromal symptoms and the lesion developed in winter, far beyond the tick bite transmission season. Because the single lesion was not pruritic and erupted on a site that was covered by clothing, patch tests for contact dermatitis were not warranted. The lesion demonstrated far less scale than is seen in psoriasis; the absence of tender, crusted vesicles ruled out impetigo.