History
Patients present with days to months, or even years, of a pruritic eruption, which usually starts on the legs. It may also burn or sting.
Nummular eczema often waxes and wanes with winter; cold or dry climates or swings in temperature may be exacerbating factors. It may improve with sun or humidity exposure or with moisturizer use. Occasionally, it may worsen with heat or humidity.
Recurrent nummular eczema lesions often occur in the same locations as previous lesions.
The patient's medical history may be positive for eczema, atopic dermatitis, or dry and sensitive skin.
Physical Examination
The diagnosis of nummular eczema is made on the basis of observing the characteristic round-to-oval erythematous plaques. They are most commonly located on the extremities, particularly the legs, but they may occur anywhere on the trunk, hands, or feet. [27] Nummular eczema does not involve the face and scalp. Lesions are often symmetrically distributed. Plaques may be several centimeters.
See the image below.
Dry, scaling plaque of nummular dermatitis (size, 3 X 5 cm) on the shin.
Lesions begin as erythematous-to-violaceous papules or vesicles, which then coalesce to form confluent plaques. They may have overlying erosions due to excoriation.
Early lesions, particularly vesicular ones, often become colonized by staphylococci, which produces a yellowish crust. Secondary overt infection may occur, with cellulitis surrounding the plaques, requiring oral antibiotics.
Within a few days, plaques become dry, scaly, and more violaceous, particularly when located below the knee.
The lesions then flatten to macules, usually with brown postinflammatory hyperpigmentation that gradually lightens. The pigment may never completely fade, particularly when located below the knee.
Lesions may demonstrate the yellow crusting of secondary impetiginization. Older plaques typically show scale that trails the lesional border.
Plaques may show central clearing, making differentiation from tinea corporis based on clinical findings difficult. Tinea corporis usually has few vesicles, a raised narrow border, and leading scale (ie, scale on the outside of the plaque).
Distinguishing among forms of dermatitis (eg, asteatotic eczema, atopic dermatitis, nummular eczema) may be difficult, but, fortunately, this is not necessary to make proper treatment decisions. [28] Contact dermatitis may have a pattern that approximates the manner in which the offending agent came into contact with the skin, such as a linear pattern. It may become chronic in the setting of repeated exposure, such as with chromates and formaldehyde. The patient may recall contact with an allergen, such as poison ivy.
Longstanding lesions that have been aggressively scratched may develop lichen simplex chronicus. This often occurs on the lower legs, neck, scalp, or scrotum. The typical erythema of nummular eczema becomes violaceous and thickened. Although the border of lichenified lesions remains well demarcated, in some areas it may become less so, particularly on the genitalia.
Stasis dermatitis may occur simultaneously on the lower extremities, and venous stasis may lead to the concomitant development of both conditions.
Complications
Nummular eczema lesions may become secondarily infected. Heavily excoriated or infected lesions may leave permanent scars. Lesions on the lower extremities take a long time to heal and may leave permanent brown macules. Cellulitis rarely occurs. Particularly pruritic cases may result in difficulty sleeping and concentrating.
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Dry, scaling plaque of nummular dermatitis (size, 3 X 5 cm) on the shin.
