(See also Definition of Dermatitis.)
Many patients with nummular dermatitis are atopic. In these cases, nummular dermatitis is simply a localized manifestation of atopic dermatitis (nummular atopic dermatitis). Patients with atopic dermatitis can have nummular plaques side-by-side with other, more common manifestations of atopic dermatitis. However, some patients with nummular dermatitis do not have atopy. In these patients, the etiology is unclear. Bacterial colonization or allergic contact reactions (1), either at the site of the lesions or elsewhere (autoeczematization or id reaction, dermatitis at sites remote from the site of the initial inflammatory problem or infection) are possible causes.
Nummular dermatitis is most common among middle-aged and older patients.
Plaques and patches of nummular dermatitis are erythematous and scaly, typically intensely pruritic, and are coin-shaped and well-demarcated but not sharply. They can number from 1 to about 50 and tend to be from 2 to 10 cm in diameter. They are often more prominent on the extensor aspects of the extremities and on the buttocks but also appear on the trunk.
Diagnosis of nummular dermatitis is clinical and based on the characteristic appearance and distribution of the skin lesions. Patients should be evaluated for atopy. In nonatopic patients, allergic contact dermatitis should be considered, and patch testing may be helpful.
Differential diagnoses include
Treatment of nummular dermatitis is similar to that of atopic dermatitis and includes counseling, antipruritics, corticosteroids, and sometimes phototherapy (particularly narrowband ultraviolet B).
Dupilumab, topical calcineurin inhibitors (tacrolimus and pimecrolimus), and/or crisaborole should be considered for nummular atopic dermatitis.
Rarely, systemic immunosuppressants are required.
Nummular dermatitis is often a manifestation of atopic dermatitis; in nonatopic patients, the etiology of nummular dermatitis is unknown.
Patients present with single or multiple pruritic coin-shaped, well-demarcated, erythematous scaly patches or plaques.
Diagnosis is clinical; skin infections and psoriasis must be excluded.
Treatment includes topical corticosteroids and phototherapy; systemic immunosuppressants are rarely needed.