1.1.2.4 Nummular Dermatitis

Discoid eczema; Nummular eczema; Dermatits nummularis.

Not fully known. Microbial colonization and microtrauma as well as nickel or preservatives contact allergy play a role. Sometimes it is associated with dry skin (asteatotic eczema) and stasis dermatitis due to chronic venous insufficiency and to cardiac or hepatic failure associated edema. In many cases (children) can manifest as a feature of atopic dermatitis (nummular type). Often a systemic focal infection can drive the disease such as tooth granulomas and chronic tonsillitis. In adults, varicose veins may trigger nummular dermatitis.

Nummular (= coin-shaped), exudative patches and plaques, often with crusts. Early lesions: confluence of papules or papulo-vesicles on an erythematous base to form circular or oval plaques. Progression to a more scaly stage with a central clearing and peripheral extension. Pruritus may be intense, sometimes with excoriations.

Sites of predilection: upper and lower shins, hands, forearms, trunk. Occasionally in a symmetrical distribution.

Different patterns: Discoid eczema of the hands and forearms (women often as a single plaque: dorsa of the hands and fingers).

Discoid eczema of the limbs and trunk (male patients: lower legs, limbs and trunk). “Dry” discoid eczema (non-itchy, persistent).

KOH examination to exclude tinea infection.

Typical histology for spongiotic dermatitis reflecting the acute/subacute or chronic nature of the lesion (see Atopic Dermatitis). The chronic type has to be differentiated from psoriatic plaques.

Secondary bacterial and mycotic infections.

The spectrum of differential diagnoses is quite large: tinea corporis, psoriasis of chronic plaque type, irritant and allergic contact dermatitis, stasis dermatitis, cutaneous T-cell lymphoma, secondary impetiginization of pre-existing lesions.

Prevention: the first step is hygiene measures, but avoiding over-washing of the skin. Emollients and avoidance of irritants are necessary.

The most often used topical treatments are corticosteroids of different strength or combinations of corticosteroids with antiseptics such as triclosan. Occasionally oral antibiotics can be necessary when a systemic focus has been detected. For acute lesions one should use local drying measures with antiseptics and astringent substances. In cases where the course is chronic, if the disease is very itchy or if the quality of life is markedly reduced, dupilumab and tralokinumab could be potentially effective therapeutic options. Systemic corticosteroids and immunosuppressive agents may also be administered, if an infectious focus is ruled out or properly treated.