Nummular eczema
Also called discoid eczema, nummular dermatitis
Coin-shaped, intensely itchy eczematous plaques, classically on the legs of older adults with dry skin. Its whole examination identity is what it is not, a filled-in coin, not tinea's ring.
How it looks
Multiple round, coin-shaped, erythematous plaques with overlying scale and crust on the shins, without central clearing.
Rose is the lesion, grey the pattern the lesions make, green where on the body it lives.
Across skin tones
Plaques often look hyperpigmented or violaceous rather than red in deeply pigmented skin, and resolve with prolonged pigment change.
Symptoms & course
- Marked itch
- Worse in winter and with dry skin
Diagnostic approach
- KOH scraping when tinea is plausible, the classic mimic pair
- Otherwise clinical
Differential, and how to separate them
- Tinea corporis
Favours it: Central clearing, advancing scaly border, KOH positive
Against it: Nummular plaques are uniformly involved across the disc
- Psoriasis
Favours it: Silvery scale, extensor sites, nail changes
Against it: Nummular lesions are itchier, weepier, and coin-perfect
Management principles
- Aggressive emollients
- Moderate-to-potent topical corticosteroids
- Treat any secondary infection
Clinical pearl: Before calling anything nummular eczema, ask what a KOH would show, this is the most commonly steroid-treated tinea mimic.
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