Chapter 148. Nummular Eczema

A 2-year-old Hispanic male presents to the clinic with erythematous, round, moist, crusted lesions on the left thigh (Figure 148-1) and right arm. His mother noted several small bumps initially, which developed into coin-shaped lesions over the next few weeks. The child is scratching them but is otherwise healthy. A KOH preparation of the scraping from the lesions did not show fungal structures. The child responds well to treatment with topical midpotency corticosteroids, emollients, and dressing in long-sleeve clothes to prevent scratching the lesions. His nummular eczema resolved in 6 weeks.

Nummular eczema (NE) is a type of eczema characterized by circular or oval-shaped scaling plaques with well-defined borders. The term nummular refers to the shape of a coin (Latin for coin is nummus). The lesions are typically multiple and most commonly found on the dorsa of the hands, arms, and legs. It often overlaps with other clinical types of eczema: atopic dermatitis, stasis dermatitis, and asteatotic eczema.1,2

Nummular dermatitis, discoid eczema, microbial eczema, and orbicular eczema.

• Prevalence is reported to range widely from 0.1% to 9.1%.1
• It is slightly more common in males than in females.1
• Males are also affected at a later age (peak older than age 50 years) than females (peak younger than age 30 years).1
• It is less common in children.

Many factors have been reported in association with NE but their role in the etiology and pathogenesis is not well established:

• NE has been viewed as microbial in origin, either secondary to bacterial colonization or hematogenous spread of bacterial toxins,1,3 but an infectious source is not identified in most cases of NE.
• NE is reported to be associated with xerosis of the skin that subsequently weakens the skin barrier function and sensitizes it to environmental allergens.4
• NE is frequently reported in association with contact sensitization to various agents, including nickel, chromate, balsam of Peru, and fragrances. Allergic or chronic contact dermatitis has been frequently reported to manifest as NE on the dorsa of the hands.1,5
• Onset of NE has been reported in association with various medications, including interferon and ribavirin therapy for hepatitis C6,7 and isotretinoin.8 Most of these reports are based on single or limited number of cases.
• Mercury in the dental amalgam was reported to induce NE in two cases with relapsing NE.9

History

• Onset is reported to be within days to week. Simultaneous or subsequent development of multiple lesions is often reported.
• Intense pruritus or burning is common.
• Lesions may last months to years without treatment and may be recurrent.
• History of medications, atopy, and exposure to allergens may be helpful to tailor the management of NE.

Physical Examination

• Primary morphology includes small papules and vesicles that coalesce to form circular to oval shape patches and plaques (Figures 148-2 and 148-3).
• Secondary morphology includes abrasion and excoriations from scratching (Figure 148-1), weeping and crusting after the vesicles leak (Figures 148-2, 148-3, and 148-4), and scaling and lichenification in more chronic lesions (Figures 148-5 and 148-6). Excessive weeping and crusting may indicate secondary bacterial infection.

Typical Distribution

• Dorsal hand is most commonly affected (Figures 148-2 and 148-7). The extensor aspects of the forearm (Figures 148-3 and 148-6) and the lower leg (Figure 148-5), the thighs (Figure 148-1), and the flanks are frequently involved, but NE may be seen in any part of the body (Figures 148-4, 148-8, and 148-9).

Laboratory Testing

• Diagnosis in most cases is made from clinical features.
• KOH preparation is helpful to investigate for tinea corporis.
• Patch testing may be considered if contact allergy is suspected.

Biopsy

• Biopsy is rarely needed, but should be performed if there is suspicion of other serious clinical entities (e.g., mycosis fungoides, psoriasis) or if the diagnosis is uncertain.

• Tinea corporis may present as pruritic annular lesions with scales and vesicles. Vesicles are typically at the periphery of the lesion compared to NE, where they are also seen in the center. A positive KOH preparation for hyphae can help with the diagnosis (see Chapter 138, Tinea Corporis).
• Psoriasis typically presents with thickened plaques on the extensor surfaces of arms and legs, scalp and sacral areas. Nail changes may be present (see Chapter 152, Psoriasis).
• Lichen simplex chronicus usually presents as a single plaque in an area easily accessible to scratching such as the ankle, wrist, and neck (see Chapter 149, Self-Inflicted Dermatoses).
• Mycosis fungoides is a type of cutaneous T-cell lymphoma, which may present with scaly patches or plaques that are often pruritic and usually erythematous. A biopsy can help make the diagnosis (see Chapter 176, Mycosis Fungoides).
• Nummular lesions of atopic dermatitis may have features similar to NE. Presence of other lesions typically on flexural surfaces, and a history of atopy, asthma, or seasonal allergies may help make the diagnosis (see Chapter 145, Atopic Dermatitis).
• Contact dermatitis (CD) may present with nummular lesions. History of exposure to contact allergens at the affected areas can raise the suspicion for CD. Patch testing may be used to confirm the clinical suspicion (see Chapter 146, Contact Dermatitis).
• Asteatotic dermatitis may have overlapping features with NE but has a less-well-defined margin.

• Emollients are beneficial to help restore and maintain normal skin barrier function. SOR C
• Hydration by bathing before bedtime followed by ointment application to wet skin is reported as an effective method of skin care in patients with eczema.10 SOR B
• A medium- to high-potency topical corticosteroid ointment is the first line of treatment. A cream preparation may be used if patient compliance is a concern with ointments. SOR C
• Topical calcineurin inhibitors such as topical tacrolimus and pimecrolimus have the benefit of not causing skin atrophy and have been shown to be effective in many types of eczema.1 SOR B They have a higher cost compared to topical corticosteroids and have a black box warning because of a reported risk of malignancies.
• Short courses of systemic corticosteroids may be necessary in severe or acute cases. SOR C
• Methotrexate is reported to be safe, effective, and well-tolerated in treatment of moderate to severe childhood NE.11 This was reported in a case series of 25 pediatric patients with refractory NE treated with 5 or 10 mg of methotrexate per week. Sixty-four percent had total clearance after an average of 10.5 months. No serious adverse events were observed in this study.11 SOR B
• Phototherapy may be used in generalized, severe, or refractory cases.1,2 Narrow-band UVB is commonly used and psoralen UVA has been used in more severe cases.2 SOR C
• Topical and oral antihistamines are often needed to treat pruritus. Topical doxepin is reported to be effective in treatment of pruritus associated with eczematous conditions and has a favorable safety profile.12 SOR B
• Topical and systemic antibiotics may be needed to treat secondary or associated bacterial infection. SOR C
• Complementary therapy with probiotics is not effective in treatment of eczema and carries a small risk of adverse events.13 SOR A

Regular follow-up is needed for the patient with chronic, refractory, or relapsing nummular dermatitis until remission or resolution is achieved.

Hydration and protection of skin form irritants is important. Apply moisturizer or topical medications immediately after bathing while the skin is still moist. Avoid strong soaps and use mild fragrance-free soap, or soap alternatives. Avoid tight clothing and fabrics that irritate the skin.

Patient Resources

• American Academy of Dermatology. Nummular Dermatitis—http://www.aad.org/skin-conditions/dermatology-a-to-z/nummular-dermatitis.
• British Association of Dermatologists. Discoid Eczema—http://www.bad.org.uk/site/811/Default.aspx.

Provider Resource

• Medscape. Nummular Dermatitis—http://emedicine.medscape.com/article/1123605.