Nummular Eczema
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Direct answer
Nummular eczema is a chronic eczematous dermatitis that forms coin-shaped, well-demarcated, exudative and crusted plaques, usually on the lower legs, forearms, dorsa of the hands and trunk. It is linked to xerosis, minor trauma, insect bites and venous stasis in older patients, and it often worsens in dry weather. Diagnosis is clinical, and treatment uses emollients, short courses of potent topical steroids and antibiotic cover when secondary infection is present.
What you must remember
- Morphology: round or oval, coin-sized plaques with vesicles, serous exudate and crusts on an erythematous base.
- Sites: lower legs, forearms, dorsa of the hands, trunk and buttocks, often in dry skin.
- Associations: xerosis, mechanical trauma, insect bites, venous stasis in older patients, and contact sensitisation.
- Pathogenesis: a weakened skin barrier with dryness and irritation starts the lesions, and atopy is a recognised risk factor.
- Histology: spongiosis, acanthosis and a superficial perivascular lymphocytic infiltrate, all non-specific.
- Differential diagnosis: tinea corporis, psoriasis, stasis dermatitis and cutaneous T-cell lymphoma, which must be considered in chronic plaques that resist treatment.
- Treatment: emollients, potent topical corticosteroids in courses for flares, wet dressings for weeping lesions and topical calcineurin inhibitors on the face and flexures.
Nummular eczema against its mimics
Nummular eczema is often mistaken for fungal infection or psoriasis, and the table separates the three in the way exam stems usually describe them.
| Feature | Nummular eczema | Tinea corporis | Plaque psoriasis |
|---|---|---|---|
| Surface | Crusts, serous weeping and exudate | Fine peripheral scale | Thick silvery scale |
| Border | Well-demarcated coin shape | Active, advancing annular border | Sharply demarcated plaque |
| Centre | Usually uniform | Central clearing in a ring | Uniform |
| Confirmation | Clinical; patch testing if allergy is suspected | KOH microscopy or culture | Clinical; biopsy if unclear |
Crusted, weeping coins with a history of dry skin or trauma favour nummular eczema, whereas an advancing ring with central clearing points to tinea. A KOH preparation settles the question when the picture is unclear, before any steroid is applied.
Patch testing is worth considering when a nummular lesion appears after a new topical product, because allergic contact dermatitis can mimic the plaques. Dermatology teaching also stresses that the eczema tends to recur at the same sites, so patients need a maintenance emollient plan from the outset.
Where the exam tries to catch you
Nummular eczema questions test the mimics, the steroid trap and the role of infection.
- Trap: applying a potent steroid to a coin-shaped plaque without a KOH test Correct: steroids can worsen dermatophytosis, so fungal infection must be excluded first.
- Trap: using potent steroids continuously for chronic plaques Correct: steroids are given in short courses for flares, with emollients for maintenance.
- Trap: ignoring exudate and crusts Correct: weeping lesions suggest secondary infection and need antiseptic dressings and antibiotic cover.
- Trap: missing venous stasis in an older patient with leg lesions Correct: stasis care and compression are part of management, because the eczema is partly driven by venous disease.
Frequently asked questions
How does nummular eczema differ from tinea corporis?
Nummular eczema forms uniform, weeping and crusted coins, whereas tinea corporis forms a scaly ring with an advancing active border and central clearing. A potassium hydroxide preparation confirms tinea corporis. Steroids should be avoided on lesions until fungal infection is excluded.
What is the first-line treatment for nummular eczema?
Emollients, short courses of potent topical corticosteroids for flares and wet dressings for weeping lesions form the usual first-line treatment for nummular eczema. Topical calcineurin inhibitors are preferred on the face and flexures. Secondary infection is treated with appropriate antibiotic cover.
Why does nummular eczema often affect the lower legs?
Nummular eczema often affects the lower legs in older patients with venous stasis and in dry skin exposed to minor trauma. The barrier is weakened in these areas, so irritation and scratching start the lesions. Compression and stasis care are important in such patients.
Does nummular eczema need a biopsy for diagnosis?
Nummular eczema is diagnosed clinically in most patients, because the coin shape and weeping pattern are characteristic. Histology shows spongiosis, acanthosis and a superficial lymphocytic infiltrate, which are non-specific. A biopsy is reserved for chronic plaques that do not respond, to exclude cutaneous lymphoma.