A 25-year-old man presented with mildly pruritic weeping lesions, one on each shin, of approximately a year’s duration. He had treated himself with various over-the-counter medications, including topical bacitracin and polymyxin B, without much success. He had a history of childhood atopic dermatitis. There was no family history of skin problems.
Physical examination revealed 2 erythematous plaques with yellowish oozing and crusting, symmetrically distributed on the anterior tibial region bilaterally. The plaques were large and round. There were no skin lesions in other locations. The rest of the physical examination findings were normal.
Answer: Nummular eczemaSee the full case at Consultant360
Nummular eczema, also known as discoid eczema or nummular dermatitis, is an inflammatory skin disorder characterized by multiple, pruritic, well-demarcated, coin-shaped or oval plaques with a well-defined border.1-3 The word nummular is from Latin and means “resembling coins.” The condition was first described by Devergie in 1854.4
The reported prevalence varies widely from 0.1% to 9%.5 The high rate reported in some studies might be due to the inclusion of patients with disseminated eczema. The condition is rare in the first year of life, and thereafter the incidence increases with age.5 The age at onset peaks between 15 and 25 years, and again between 55 and 65 years.5 The condition is slightly more common in males than in females.3 No racial predilection has been observed.
The exact pathogenesis has not been clarified, but it is likely multifactorial. The neuropeptides substance P, calcitonin gene-related peptide (CGRP), and mast cells are more frequent in the epidermis and papillary dermis in patients with nummular eczema.6,7 The increase in the neuropeptides substance P and CGRP might stimulate keratinocytes to release cytokines, which enhance inflammation.6
Infections, in particular Staphylococcus aureus infection, might play a role either directly or through a hypersensitivity mechanism.8,9 Helicobacter pylori infection has also been implicated in the pathogenesis in some cases.10
Nummular eczema is more frequent in persons with atopy and can develop after contact with nickel, chromate, cobalt, fragrances, wool, soaps, rubber, thimerosal, formaldehyde, or topical medications (neomycin and thioglycolate).1,2,11,12 It is exacerbated by conditions that promote xerotic skin such as frequent bathing, low humidity, windy environments, and the winter season.1,13 Xerotic skin allows epidermal breach and permeation of environmental allergens that may induce an allergic or irritant response.1,2,11,14 Systemic medications such as isotretinoin, streptomycin, isoniazid, interferon, ribavirin, tumor necrosis factor inhibitors, and methyldopa have also been implicated in the pathogenesis.11,14,15
Nummular eczema is a potential complication of breast reconstruction with tissue expanders and silicone implants.16 Emotional stress can precipitate or exacerbate nummular eczema in a susceptible individual.1 Other predisposing factors include alcohol or tobacco consumption, local trauma, venous stasis, and edema of the lower limbs.11 Nummular eczema may be a sign of an internal pathologic condition such as pernicious anemia or diabetes mellitus.5
Histopathology and Clinical Manifestations
Histologic findings in the acute stage include intercellular edema, intraepidermal vesicles, and perivascular lymphocytic infiltration.5,7 Chronic changes include hyperkeratosis, acanthosis, an increase in the granular cell layer, and hyperplasia of the epidermis.5
Nummular eczema is characterized by sharply defined, coin-shaped to oval, erythematous, eczematous plaques.1-3 The initial lesions are uniform groups of erythematous papules and vesicles, which with time and itching, become inflamed and might weep.5 The lesions enlarge by confluence or peripheral extension to form the discrete, round or oval, erythematous, scaly, lichenified, hyperkeratotic, and hyperpigmented plaques that are typical of chronic nummular eczema.5 The size of the lesion varies from 1 to 10 cm in diameter.3 The lesions are usually symmetric and pruritic.7 Sites of predilection include the lower extremities, followed by the upper extremities, although the lesion may also occur on the trunk, neck, and face.1,3,12,15
Diagnosis and Differential Diagnosis
The diagnosis is mainly clinical based on the characteristic features of the lesions. Biopsy or laboratory tests are generally not necessary. However, a potassium hydroxide wet-mount examination of skin scrapings should be performed if tinea corporis is suspected. Because contact allergy is common with nummular eczema, patch testing should be considered in patients with chronic, recalcitrant nummular eczema.2,3,17
Nummular eczema should be distinguished from tinea corporis, impetigo, plaque psoriasis, granuloma annulare, allergic contact dermatitis, atopic dermatitis, and stasis dermatitis. Crusting surface, lack of central clearing, typical locations of the lesions, and past history of atopic dermatitis help distinguish lesions of nummular eczema from tinea corporis.13 Impetigo is characterized by a thick, golden-yellow “stuck-on” crust. The scales in nummular eczema are thin and sparse, unlike the thick, silvery scales of plaque psoriasis. Pinpoint bleeding after removal of the superficial scales (Auspitz sign), pitting of the nails, and arthropathy suggest plaque psoriasis. Granuloma annulare is characterized by dermal papules, which often assume an annular configuration. In allergic contact dermatitis, the site, configuration, and chronicity of the skin lesions help differentiate the lesion from nummular eczema.18 The patient may recall contact with an allergen. In contrast to atopic dermatitis, which has an indistinct border and the unaffected skin is xerotic, nummular eczema has a clearly defined margin, and the unaffected skin is usually not xerotic.19 A history of atopic disease and occurrence of the lesions in typical flexural locations supports the diagnosis of atopic dermatitis.19 A history of venous insufficiency and the presence of varicose veins, pitting edema, and hyperpigmentation support the diagnosis of stasis dermatitis.3
Nummular eczema has a significant negative impact on health-related quality of life due to pruritus, discomfort, esthetic concerns, social embarrassment, and impairment of professional performance.5,7 Affected individuals may have lower self-esteem. Secondary bacterial infection, especially with S aureus, may occur.8 Patients with nummular eczema are at increased risk of developing allergic contact dermatitis, which in turn may contribute to the severity and chronicity of nummular eczema.2 Chronic lesions that have been vigorously scratched may develop lichen simplex chronicus.
Prognosis and Management
Nummular eczema can be treated and cleared successfully over a few weeks, although the course can be chronic and characterized by relapses and remissions in some cases.1,3
Successful treatment requires avoidance of precipitating factors along with optimal skin care and pharmacotherapy. Any underlying condition, if identified, should be treated. Hydration of the skin is important in that it helps to improve the dryness and pruritus and restore the disturbed skin’s barrier function. Daily baths in lukewarm but not hot water for 5 to 10 minutes, followed by gently patting rather than rubbing the skin dry, are helpful. A quality moisturizer, emollient, or barrier cream (preferably one with ceramide or ceramide precursor) should be used liberally and regularly to keep the skin soft and well hydrated and to prevent transepidermal water loss. The moisturizer or emollient should be applied within 3 minutes of bathing to minimize evaporative losses.
Potent topical corticosteroids are the mainstay of therapy.12 Corticosteroids should not be applied more than twice a day; frequent use does not improve efficacy and increases the risk of adverse effects. Topical immunomodulators such as tacrolimus and pimecrolimus are not as fast or effective as potent topical corticosteroids in the treatment of nummular eczema, although they can be considered in the maintenance phase. Patients with generalized severe or refractory disease may require treatment with narrowband UV-B phototherapy, systemic corticosteroids, systemic methotrexate, or systemic cyclosporine.3,12
Although pruritus in nummular eczema does not appear to be mediated by histamine release, oral antihistamines can provide symptomatic relief to some patients because of their sedative properties and may be effective for intense pruritus that is refractory to moisturizers and conservative measures. Of the H1 antihistamines, hydroxyzine is more effective than diphenhydramine and cyproheptadine.5
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3. Zirwas MJ. Nummular eczema. UpToDate. http://www.uptodate.com/contents/nummular-eczema. Updated August 1, 2016. Accessed December 7, 2016.
4. Devergie A. Traité Pratique des Maladies de la Peau. Paris, France: Librairie de Victor Masson; 1854:237.
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18. Leung AKC, Barankin B. An annular lesion in the elbow. Am Fam Physician. 2016;93(5):397-398.
19. Leung AKC, Hon KLE. Atopic Dermatitis: A Review for the Primary Care Physician. New York, NY: Nova Science Publishers; 2011.