Differential diagnosis of annular lesions

Although most annular lesions will be typical of a dermatophytosis, physicians must consider other possible diagnoses. Tinea corporis can often be diagnosed on the basis of a positive potassium hydroxide examination. Topical and systemic antifungals are usually curative. Pityriasis rosea is characterized by small, fawn-colored lesions distributed along skin cleavage lines. Treatment is symptomatic. Granuloma annulare is characterized by nonscaly, annular plaques with indurated borders, typically on the extremities. One half of cases resolve spontaneously within two years. Sarcoidosis can present as annular, indurated plaques similar in appearance to the lesions of granuloma annulare. Diagnosis is based on histopathology and the involvement of other organ systems. Hansen's disease can mimic tinea corporis by presenting as one or more annular, sometimes scaly, plaques. Urticaria may affect 10 to 20 percent of the population. The annular plaques lack scale and are evanescent. Subacute cutaneous lupus erythematosus can present in an annular form on sun-exposed surfaces or in a papulosquamous form. Erythema annulare centrifugum typically presents as annular patches with trailing scale inside erythematous borders.