Nummular eczema is a chronic eczema characterised by coin-shaped, sharply demarcated lesions. As it overlaps with other forms of eczema (atopic dermatitis, asteatotic eczema, allergic contact dermatitis, stasis dermatitis), it has been questioned if it is an independent clinical entity. Nummular eczema is more common in males. The traditional view of this eczema subtype as being caused by microbial agents has not been confirmed.
Clinical picture: Round erythematous sharply-demarcated patches are characteristic of this disorder. Vesicles and weeping may be present, but more often the patches are hyperkeratotic and lichenified. The accompanying itching may be severe.
Distribution: Typically the distal limbs are affected, particularly the back of hands, feet, forearms and legs. Rarely the shoulders and upper back are also involved.
Diagnosis: The diagnosis is based on a careful history and the clinical picture. To detect superinfections, bacterial swabs should be taken, as well as mycological cultures to exclude tinea. Patch testing allows an exclusion of underlying allergies.
Differential diagnoses: Nummular lesions of atopic dermatitis as well as stasis dermatitis, asteatotic eczema and allergic contact dermatitis should be distinguished. Tinea corporis, psoriasis, Bowen’s disease and mycosis fungoides also have to be considered.