Nummular dermatitis, or nummular eczema, is an inflammatory skin condition that is considered to be a distinctive form of idiopathic eczema, while the term also is used to describe lesional morphology associated with other conditions.
The term nummular derives from the Latin word for “coin,” as lesions are commonly annular plaques. Lesions of nummular dermatitis can be single or multiple. The typical distribution involves the extremities and, although less common, it can affect the trunk as well.
Nummular dermatitis may be associated with atopic dermatitis, or it can be an isolated condition.1 While the pathogenesis is uncertain, instigating factors include xerotic skin, insect bites, or scratches or scrapes.1Staphylococcus infection or colonization, contact allergies to metals such as nickel and less commonly mercury, sensitivity to formaldehyde or medicines such as neomycin, and sensitization to an environmental aeroallergen (such as Candida albicans, dust mites) are considered risk factors.2
The diagnosis of nummular dermatitis is clinical. Laboratory testing and/or biopsy generally are not necessary, although a bacterial culture can be considered in patients with exudative and/or crusted lesions to rule out impetigo as a primary process of secondary infection. In some cases, patch testing for allergic contact dermatitis may be useful.
The differential diagnosis of nummular dermatitis includes tinea corporis (ringworm), atopic dermatitis, allergic contact dermatitis, impetigo, and psoriasis. Tinea corporis usually presents as annular lesions with a distinct peripheral scaling, rather than the diffuse induration of nummular dermatitis. Potassium hydroxide preparation or fungal culture can identify tinea species. Nummular dermatitis may be seen in patients with atopic dermatitis, who should have typical history, morphology, and course consistent with standard diagnostic criteria. Allergic contact dermatitis can present with regional, localized eczematous plaques in areas exposed to contact allergens. Patterns of lesions in areas of contact and worsening with repeat exposures can be clues to this diagnosis. Impetigo can present with honey-colored crusted lesions and/or superficial erosions, or purulent pyoderma. Lesions can be single or multiple and generally appear less inflammatory than nummular dermatitis. Psoriasis lesions may be annular, are more common on extensor surfaces, and usually have more prominent overlying pinkish, silvery white or micaceous scale.
Management of nummular dermatitis requires strong anti-inflammatory medications, usually mid-potency or higher topical corticosteroids, along with moisturizers and limiting exposure to skin irritants. “Wet wraps,” with application of topical corticosteroids to wet skin with occlusive wet dressings can enhance response. Transition from higher strength topical corticosteroids to lower strength agents used intermittently can help achieve remission or cure. Management practices include less frequent bathing with lukewarm water, using hypoallergenic cleansers and detergents, and applying moisturizers frequently. If plaques do recur, they tend to do so in the same location and in some patients resolution may result in hyper or hypopigmentation. Refractory disease may be managed with intralesional steroid injections, or systemic medications such as methotrexate.3
Dr. Tracy is a research fellow in pediatric dermatology at Rady Children’s Hospital–San Diego and the University of California, San Diego. Dr. Eichenfield is chief of pediatric and adolescent dermatology at Rady Children’s Hospital–San Diego. He is vice chair of the department of dermatology and professor of dermatology and pediatrics at the University of California, San Diego. Neither Dr. Tracy nor Dr. Eichenfield have any relevant financial disclosures. Email them at.