A Persistent Itchy Rash on the Leg of a College Athlete

Nummular eczema, also known as discoid eczema or nummular dermatitis, is named for its distinct coin-shaped lesions. These lesions are typically found in groups on the trunk and extremities1 and are often intensely pruritic. This condition can persist for months...

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Nummular eczema, also known as discoid eczema or nummular dermatitis, is named for its distinct coin-shaped lesions. These lesions are typically found in groups on the trunk and extremities¹ and are often intensely pruritic. This condition can persist for months to years despite treatment, with frequent relapses possible.² 

The prevalence of nummular eczema is approximately 0.1% to 9.1%.³ Men aged ≥40 years are more commonly affected while the condition affects women more often at age ≤30 years. The overall incidence of disease is higher in men than in women.³ 

Traditionally, nummular eczema was thought to be of endogenous etiology; however, the exact cause is unknown and is likely multifactorial. Risk factors include dry skin, winter and summer weather, Staphylococcus, emotional stress, allergies, poor circulation, and edema of the lower extremities.¹ Two-thirds of patients with nummular eczema are found to have dry skin. Fragrances, cosmetics, chrome, nickel, alcohol, neomycin, and isotretinoin are possible triggering allergens.² One theory of pathogenesis postulates that an impaired cutaneous barrier, caused by dry skin, allows allergens to permeate the skin and cause an immunologic reaction.⁴

On examination, lesions typically present as 1-cm to 3-cm, well-demarcated, scaly, erythematous, coin-shaped plaques found primarily on the extremities and trunk. Commonly affected areas include the dorsum of the hands, as well as extensor surfaces. Lesions may also present with crusts, vesicles, excoriations, and serous exudate.¹ A single round lesion may present initially.⁵ More lesions may appear and can expand to form raised plaques with peripheral vesicular borders and central erythema.⁶ Honey-colored crust on the lesions may indicate a secondary staphylococcal infection.⁷

Dermoscopic examination of the lesions may show yellow clods, scales, crusts, or red-brown globules. The yellow clods are 1-mm to 2-mm accumulations of serous exudate, best seen when the lesion is wet. Histopathologic examination can show spongiosis, irregular acanthosis, parakeratotic scaling and inflammatory cell infiltration of the superficial dermis and epidermis.⁸ 

The differential diagnosis of round, erythematous lesions includes tinea corporis, psoriasis, mycosis fungoides, lichen aureus, allergic contact dermatitis, and atopic dermatitis.² The diagnosis of nummular eczema is made clinically based on patient history and physical examination findings. A biopsy can be obtained to rule out skin conditions like mycosis fungoides; however, histopathologic findings are similar to those found in other types of subacute or chronic eczema.^5,8 A patient with lesions on the flexor surfaces or with a history of allergies, asthma, or atopy makes atopic dermatitis the more likely diagnosis.³ 

The presence of multiple yellow clods on dermoscopic examination can help distinguish nummular eczema from tinea corporis and psoriasis.⁹ Tinea corporis lesions are round with central clearing and have peripheral erythema and scaling. KOH preparation of lesion scrapings can be analyzed microscopically to rule out dermatophytic infection.⁴ A patient presenting with thick, silvery plaques and nail changes likely has psoriasis. Compared with nummular eczema, psoriasis lesions have a more symmetric distribution with involvement of the head and neck.³ Lichen aureus is a type of pruritic pigmented dermatosis. The lesions are round, rust-colored plaques that are found mainly on the extremities. Dermoscopy and histopathology can be used to differentiate this condition from nummular eczema.¹⁰ 

The role of hypersensitivity reactions in nummular eczema is unclear. Contact dermatitis can also present with round lesions after an exposure and can mimic nummular eczema. Patch testing can be used to identify allergens and irritants that contribute to lesion formation.² Patch test will be positive in one-third to one-fourth of patients with nummular eczema.⁷

First-line treatment for this condition includes moderate- to high-potency topical corticosteroids or topical calcineurin inhibitors. Emollients help to keep the skin hydrated.² Antihistamines may be prescribed to help reduce itching, especially during the night. Topical antibiotics, like mupirocin, or oral antibiotics are only necessary to treat any secondary bacterial infections that may arise. Light therapy using narrow-band ultraviolet B or psoralen plus ultraviolet A may be used for refractory cases.⁷ 

In this case, our patient was given topical corticosteroids and instructed to apply the ointment to the affected area 1 to 2 times daily. She was also advised to take short lukewarm showers and to moisturize with copious amounts of Vaseline® multiple times daily. With this regimen, the lesions mostly resolved. However, the lesions returned during the summer when the patient had multiple hours of swim practice per day. She has been able to maintain control of the disease through vigilant moisturizing and early application of topical steroids at the first sign of a developing lesion.

Lauren Fuller is a medical student, Joan Fernandez is a medical student, and Christopher Rizk, MD, is a dermatology resident at the Baylor College of Medicine in Houston.

References

1. Bonamonte D, Foti C, Vestita M, Ranieri LD, Angelini G. Nummular eczema and contact allergy: a retrospective study. Dermatitis. 2012;23(4):153-157.
2. 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.
3. Reider N, Fritsch PO. Other eczematous eruptions. In: Bolognia JL, Schaffer JV, Cerroni L. Dermatology. 4th ed. Philadelphia, PA: Elsevier; 2018:228-241.
4. Rattan R, Tegta GR, Shanker V, et al. Role of contact allergens in chronicity and relapses of nummular eczema. Int J Res Dermatol. 2017;3(2):213-218.
5. Habif TP, Campbell JL, Chapman MS, Dinulos JGH, Zug KA. Skin Disease E-Book: Diagnosis and Treatment. Philadelphia, PA: Elsevier; 2017. 
6. Halburg M. Nummular eczema. J Emerg Med. 2012;43(5):327-328.
7. James WD, Berger TG, Elston DM. Atopic dermatitis, eczema, and noninfectious immunodeficiency disorders. In: Andrews’ Diseases of the Skin. 12th ed. Philadelphia, PA: Elsevier; 2016:62-89. 
8.  Moore MM, Elpern DJ, Carter DJ. Severe, generalized nummular eczema secondary to interferon alfa-2b plus ribavirin combination therapy in a patient with chronic hepatitis c virus infection. Arch Dermatol. 2004;140(2):215-217.
9. Navarini AA, Feldmeyer L, Öndury BT, et al. The yellow clod sign. Arch Dermatol. 2011;147(11):1350-1350.
10. Suh KS, Park JB, Yang MH, Choi SY, Hwangbo H, Jang S. Diagnostic usefulness of dermoscopy in differentiating lichen aureus from nummular eczema. J Dermatol. 2016;44(5):533-537.