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Nummular eczema is predominantly a disease of adulthood. Men are more frequently affected than women. The peak incidence in both males and females is around 50–65 years of age. There is a second peak in women around 15–25 years of age. Nummular eczema is rare in infancy and childhood. The peak age of onset in childhood is 5 years.1
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Etiology and Pathogenesis
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The pathogenesis of nummular eczema is still unknown. The vast majority of patients with nummular eczema do not have a personal or family history of atopy,2,3 although nummular plaques may be seen in atopic eczema. Numerous factors have been implicated as causal. The state of hydration of the skin in elderly patients has been shown to be decreased.4 The role of infection previously received much attention in the literature. An internal focus of infection, including teeth, upper respiratory tract, and lower respiratory tract, was found in 68% of patients in one study.5 Eleven of thirteen patients without a history of atopic eczema improved after odontogenic infections were treated.6 A role for environmental allergens, such as the house dust mite and Candida albicans has also been touted.4 Nummular eczema has been reported during therapy with isotretinoin and gold.7,8 Generalized nummular eczema is seen in patients with hepatitis C undergoing combination therapy with interferon α-2b and ribavirin.9,10 Mercury amalgam was implicated as a cause in two patients.11
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Well-demarcated coin-shaped plaques form from coalescing papules and papulovesicles. Pinpoint oozing and crusting eventuate, and are distinctive (Figs. 15-1 and 15-2). Crust may however cover the entire surface (Fig. 15-3). Plaques range from 1 to 3 cm in size. The surrounding skin is generally normal but may be xerotic. Pruritus varies from minimal to severe. Central resolution may occur, leading to annular forms. Chronic plaques are dry, scaly, and lichenified. The classic distribution of lesions is the extensor aspects of the extremities. In women, the upper extremities, including the dorsal aspects of the hands, are more frequently affected than the lower extremities.2 Exudative discoid and lichenoid dermatitis of Sulzberger-Garbe may represent a variant of nummular dermatitis.12
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