(See also Definition of Dermatitis Definition of Dermatitis The meaning of the word "dermatitis" is inflammation of the skin. However, in clinical dermatology, dermatitis is used to describe a variety of different skin conditions that share the same... read more .)
Many patients with nummular dermatitis are atopic. In these cases, nummular dermatitis is simply a localized manifestation of atopic dermatitis Atopic Dermatitis (Eczema) Atopic dermatitis is a chronic relapsing inflammatory skin disorder with a complex pathogenesis involving genetic susceptibility, immunologic and epidermal barrier dysfunction, and environmental... read more 
(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 General reference Nummular dermatitis is inflammation of the skin characterized by coin-shaped or discoid eczematous lesions. Diagnosis is clinical. Treatment may include topical corticosteroids and phototherapy... read more 
), 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.
General reference
1. Bonamonte D, Foti C, Vestita M, et al: Nummular eczema and contact allergy: A retrospective study. Dermatitis 23(4):153–157, 2012. doi: 10.1097/DER.0b013e318260d5a0
Symptoms and Signs of Nummular Dermatitis
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
Clinical evaluation
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
Psoriasis Psoriasis Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more
: Psoriatic plaques are typically more sharply demarcated.Tinea Overview of Dermatophytoses Dermatophytoses are fungal infections of keratin in the skin and nails (nail infection is called tinea unguium or onychomycosis). Symptoms and signs vary by site of infection. Diagnosis is by... read more : Tinea typically first manifests with annular plaques with advancing scale and central clearing over time.
Treatment of Nummular Dermatitis
Supportive care, including counseling
Antipruritics
Corticosteroids (most often topical)
Phototherapy
Treatment of nummular dermatitis is similar to that of atopic dermatitis Treatment Atopic dermatitis is a chronic relapsing inflammatory skin disorder with a complex pathogenesis involving genetic susceptibility, immunologic and epidermal barrier dysfunction, and environmental... read more 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.
Key Points
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.
