A man, aged 68 years, with no known history of atopy presents with a 4-month history of an itchy and burning rash on the legs that has been recurring every winter for the past 3 years. He notes that he had dry skin at baseline and did not use emollients, but he did try hydrocortisone 1% cream without improvement. Examination revealed ovoid, erythematous, well-marginated plaques on the lower legs and dorsal feet with variable scaling and focal weeping and crusting. There were no nail changes, and the rest of his skin examination was notable only for xerosis.
Submit your diagnosis to see full explanation.
Nummular dermatitis, also known as nummular eczema or discoid eczema, is an inflammatory condition characterized by sharply marginated, coin-shaped, erythematous plaques containing microvesicles that erode with resultant weeping, crusting, and scaling. The morphology of nummular dermatitis lesions differs from those of classic eczema, which generally consists of ill-defined, irregularly shaped, scaling patches and plaques.
Devergie initially described this condition in 1857, using the term “l’eczéma nummulaire” to emphasize the distinctive coin-shaped lesions.1 Of note, the word nummular is derived from the Latin word for coin, nummus. The condition continued to be reported by other authors under various names, including orbicular eczema, recurrent eczematoid affection, and neurotic eczema.2
Epidemiologic data regarding nummular dermatitis are limited, as the condition is not often reported in the literature, and many of the studies are decades old. Up-to-date population prevalence data are lacking. The condition is more common in adults, with a peak in the third to fourth decade of life, although children may be affected as well.3 Reports of sex-specific predilection are varied. A majority of studies report male predominance among cases, with the exception being in pediatric patients with nummular dermatitis.3-5
Patients with nummular dermatitis classically present with well-marginated, ovoid, erythematous plaques measuring up to a few centimeters in diameter with variable vesiculation, weeping, crusting, and scaling. There are often multiple lesions, with symptoms of pruritus and/or pain, and they tend to concentrate on the extremities (legs more often than arms). Truncal involvement can occur, but facial lesions are rare. The eruption usually lasts several months with frequent recurrences, and onset in colder months is typical.3-6
Many varied hypotheses on the etiology of nummular dermatitis have been proposed, but the pathogenesis has yet to be determined. Some authors consider nummular dermatitis to be a form of atopic dermatitis, but this is debated because personal or family history of atopy is not commonly reported in patients with nummular dermatitis.3-5 In addition, serum immunoglobulin E levels, which are usually elevated in patients with atopic dermatitis, are generally normal in those with nummular eczema.3 Given the predominance of lesions on the lower extremities, the role of varicose veins in the pathogenesis of the condition has been proposed, with the thought that the nummular lesions may represent an “id reaction” to stasis dermatitis seen more commonly in patients with varicosities.6 Id reactions are sympathy reactions that manifest as rashes of varying morphology distant to the inciting eruption. The prevalence of xerosis mirrors that of nummular dermatitis in that it is more common in older adults and in winter months; thus, age and weather have also been reported as a predisposing or contributing factor.3,6,7 Emotional distress, which has been reported to trigger or flare many dermatoses, has also been hypothesized to do the same in nummular eczema.6
Contact allergy has also been reported to occur at a higher frequency in patients with nummular dermatitis; it is unclear whether the contact allergy initiates the condition or whether the condition is simply complicated by superimposed contact allergy. Patients with nummular dermatitis have a skin barrier that is not intact, thus predisposing them to contact sensitization. In addition, many of these patients apply a myriad of topical preparations to their lesions, which also makes them more prone to the development of contact allergy.3 Patch testing should be considered in patients with treatment-refractory disease.
Similar to the idea that nummular dermatitis may represent an id reaction to stasis dermatitis, some have proposed that nummular dermatitis represents a skin reaction triggered by bacterial antigens released from various infectious foci (including non-skin sites such as teeth and tonsils). Patients with difficult-to-control disease have shown improvement with eradication of the distant infection.8,9 Other reported associations include excessive alcohol intake, nutritional deficiency, and medications, among others.3
The differential diagnosis of nummular dermatitis includes psoriasis, bullous impetigo, tinea corporis, and other variants of dermatitis. Psoriasis is another chronic, inflammatory condition of the skin but can be differentiated from nummular dermatitis by its appearance. Psoriasis also consists of well-marginated plaques, but the borders of psoriasis lesions are often more well-defined than those of nummular dermatitis. Psoriasis lesions are predominantly scaly, whereas nummular dermatitis lesions are typically more crusted. Bullous impetigo is more commonly seen in children and is caused by a staphylococcal infection of the skin that leads to formation of flaccid bullae that erode into ovoid, crusted plaques. Once bullous impetigo lesions have eroded and crusted, they can mimic nummular dermatitis lesions. However, patients with nummular dermatitis usually do not have a preceding history of frank bullae; their lesions consist of multiple tiny vesicles. Notably, nummular dermatitis can be complicated by bacterial superinfection, so obtaining cultures of affected skin is important. Tinea corporis is a superficial fungal infection of the skin that presents with annular, erythematous plaques with a peripheral rim of scale (also known as ringworm). Tinea corporis lesions have central clearing, which is absent in nummular dermatitis lesions. Depending on the chronicity of dermatitis, the clinical appearance varies. Acute forms of dermatitis (usually irritant or allergic contact dermatitis) can present with vesiculobullous lesions that may resemble nummular dermatitis. Contact dermatitis lesions can be localized in a specific pattern depending on the contactant. Subacute forms of dermatitis are generally erythematous and scaly and usually less well-marginated, so often, these lesions will not look like nummular dermatitis. Chronic dermatitis is usually ill-defined and lichenified, with an appearance that differs from nummular dermatitis.
The diagnosis of nummular dermatitis is made clinically. However, if the presentation is not typical or response to treatment is poor, a skin biopsy should be considered for confirmation. Histopathology reveals edema between the keratinocytes in the epidermis (spongiosis) that expands to form intraepidermal vesicles. There is an accompanying lymphohistiocytic infiltrate in the superficial dermis, concentrated perivascularly.3 This is a typical pattern for dermatitis of all types; therefore, a skin biopsy will not necessarily help to differentiate specific etiologies of dermatitis (atopic vs contact vs nummular). Special stains for infection may reveal bacteria within the stratum corneum but results are typically negative for fungus.
Topical corticosteroids are the first-line treatment for nummular dermatitis; mid- to high-potency preparations are usually required. Clinicians should keep in mind the side effects of atrophy and striae. To minimize the side effects of steroids, topical tar and topical calcineurin inhibitors have also been used successfully. Phototherapy can also be effective for widespread lesions or in patients who do not respond to conservative management. Systemic immunosuppressive therapy is reserved for the most severe and treatment-refractory patients and is considered off-label use; prednisone, cyclosporine, methotrexate, mycophenolate mofetil, or azathioprine can be considered. Patients must be closely monitored for side effects. If there is suspicion for superimposed skin infection, bacterial cultures should be obtained, with use of oral antibiotics dictated by results of cultures and sensitivities.10 All patients should be advised on proper skin care measures that include use of emollients and gentle soaps. Pruritus can be managed with antihistamines.
The prognosis for nummular dermatitis is good, and most patients respond to conservative therapy. Complications can include skin infection, and lesions usually resolve with postinflammatory hyperpigmentation.
In our case, the patient received a diagnosis of nummular dermatitis and was treated with a topical class 1 corticosteroid, with improvement.
R. Blake Steele, BS, is a medical student and Erin Reese, MD, is assistant professor and assistant residency program director in the Department of Dermatology at Virginia Commonwealth University in Richmond.
- Devergie M. Traité Pratique des Maladies de la Peau. Paris: Librarie de Victor Masson; 1857:238.
- Weidman AI, Sawicky HH. Nummular eczema; review of the literature: survey of 516 case records and follow-up of 125 patients. AMA Arch Derm. 1956;73(1):58-65.
- Bonamonte D, Foti C, Vestita M, et al. Nummular eczema and contact allergy: a retrospective study. Dermatitis. 2012;23(4):153-157.
- Hellgren L, Mobacken H. Nummular eczema—clinical and statistical data. Acta Derm Venereol. 1969;49(2):189-196.
- Cowan MA. Nummular eczema. A review, follow up, and analysis of a series of 325 cases. Acta Derm Venereol. 1961;41:453-460.
- Jiamton S, Tangjaturonrusamee C, Kulthanan K. Clinical features and aggravating factors in nummular eczema in Thais. Asian Pac J Allergy Immunol. 2013;31(1):36-42.
- Aoyama H, Tanaka M, Hara M, et al. Nummular eczema: an addition of senile xerosis and unique cutaneous reactivities to environmental aeroallergens. Dermatology. 1999;199(2):135-139.
- Pugliarello S, Cozzi A, Gisondi P, Girolomoni G. Phenotypes of atopic dermatitis. J Dtsch Dermatol Ges. 2011;9(1):12-20.
- Tanaka T, Satoh T, Yokozeki H. Dental infection associated with nummular eczema as an overlooked focal infection. J Dermatol. 2009;36(8);462-465.
- Roberts H, Orchard D. Methotrexate is a safe and effective treatment for paediatric discoid (nummular) eczema: a case series of 25 children. Australas J Dermatol. 2010;51(2):128-130.