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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. (Am Fam Physician 2001;64:289-96.)
AlphaAnnular lesions are extremely common and striking in appearance but can also be misleading. The term "annular" stems from the Latin word "annulus," meaning ringed.1 The lesions appear as circular or ovoid macules or patches with an erythematous periphery and central clearing. The most common cause of annular lesions encountered in the adult population is dermatophytosis, which may be successfully diagnosed without a biopsy. However, other conditions may present with much the same appearance (Table 1). The clinician must exclude other diagnoses, especially if the patient has failed previous treatment for dermatophytosis.
Tinea Corporis
Tinea corporis refers to a dermatophytosis or superficial fungal infection of the skin, other than on the hands, feet, scalp, face or groin.2 This condition is also commonly referred to as ringworm, a misnomer that stems from the annular appearance once believed to be caused by invasive worms. The main causes belong to three genera: Trichophyton, Microsporum and Epidermophyton. The most common cause of tinea corporis in the United States is infection with Trichophyton rubrum, Trichophyton tonsurans, Trichophyton mentagrophytes and Microsporum canis.1 All dermatophytes are aerobic, and they share the ability to assimilate keratin, thus allowing them to penetrate the keratinized layers of...