Board Review: Annular Lesions Differential Diagnosis

Overview / Definition Annular lesions are characterized by a circular or ring-like configuration with a central clearing or raised border. They can vary in size and are often symptomatic or asymptomatic. The differential diagnosis includes a wide range of dermatological conditions, making clinical acumen essential for appropriate management. Epidemiology Annular lesions can occur in patients of all ages and ethnic backgrounds. Some specific conditions, such as granuloma annulare and erythema annulare centrifugum, may have demographic predispositions. For instance: Granuloma annulare is more common in children and young adults. Erythema annulare centrifugum often presents in adults. Fungal infections like tinea corporis can occur in all demographics but may have higher incidence in immunocompromised hosts. Pathophysiology / Mechanism The mechanisms underlying annular lesions vary significantly depending on the underlying condition. For example: Granuloma annulare: An idiopathic inflammatory response involving dermal histiocytes. Erythema annulare centrifugum: Often linked to infections or malignancies, characterized by a hypersensitivity reaction. Tinea corporis: A fungal infection caused by dermatophytes leading to annular plaques due to inflammatory response. Clinical Presentation Annular lesions may present with various associated symptoms: Asymptomatic or pruritic. Variable size, with well-defined borders. Central clearing, with or without scaling or crusting. May be associated with systemic symptoms in cases linked to infections or malignancies. Diagnosis / Workup Diagnosis requires a thorough clinical examination, patient history, and sometimes laboratory tests. Key components of the workup include: Clinical evaluation: Assessing the morphology and distribution of the lesions. Skin scraping: To identify fungal elements in suspected tinea infections. Biopsy: Considered in atypical cases or to rule out malignancy. Serological tests: If an underlying systemic cond