Tinea Corporis and Pityriasis Rosea

July 1, 2008

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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Figure>Case 1:

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.

What is your clinical impression?


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

Case 2:

The parents of a 9-year-old girl are concerned about their daughter's rash that developed 1 week earlier. The asymptomatic eruption is primarily on the trunk. The patient has no history of contactant exposure, takes no medications, and has not had any recent illnesses. The family pets include a dog and a cat.

What is the most likely cause of this patient's rash?


A. Pityriasis rosea.
B. Psoriasis.
C. Tinea corporis.
D. Nummular eczema.
E. Contact dermatitis.

Dermclinic-Answers

Case 1: Tinea corporis

A potassium hydroxide evaluation confirmed tinea corporis, B, which responded to a topical antifungal. The family was advised to have their dog examined by a veterinarian because 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, long after 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.

Case 2: Pityriasis rosea

Circular patches of scaling and erythema are clues to pityriasis rosea, A, a self-limited disease that may last for weeks to months. This patient exhibits signs of both the common form of the disorder and a papular variant. A corticosteroid cream and the anti-inflammatory effect of moderate exposure to sunlight cleared the outbreak.

Psoriasis in this age group usually follows a streptococcal infection; this patient had no such history. Her rash was far too extensive to be tinea corporis. She had no history of atopy, which made nummular eczema unlikely. Contact dermatitis is pruritic and not as discrete as this patient's lesions.