Nummular Dermatitis
(Discoid Dermatitis)
(See also Definition of Dermatitis and Hand and Foot Dermatitis.)
Nummular dermatitis is most common among middle-aged and older patients and is often associated with dry skin, especially during the winter. Dermatophytid (identity, or id) reactions may manifest as nummular dermatitis. The cause of nummular dermatitis is unknown, but, occasionally, a contact allergen is identified as the cause (1).
General reference
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1. Bonamonte D, Foti C, Vestita M, et al: Nummular eczema and contact allergy: A retrospective study. Dermatitis 23(4):153–157, 2012.
Symptoms and Signs
Discoid lesions often start as patches of confluent vesicles and papules that ooze serum and form crusts. Later they become dry, scaly, lichenified, and sometimes annular (central clearing). Lesions are often intensely pruritic. 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. Exacerbations and remissions may occur, and when they do, new lesions tend to reappear at the sites of healed lesions.
Diagnosis
Treatment
No treatment is uniformly effective. Oral antibiotics (eg, dicloxacillin or cephalexin 250 mg 4 times a day) may be given, along with use of tap-water compresses, if weeping and pus are present. A mid- to high-potency corticosteroid cream or ointment should be rubbed in 2 times a day. An occlusive dressing with a corticosteroid cream under polyethylene film or with flurandrenolide-impregnated tape can be applied at bedtime. Intralesional corticosteroid injections may be beneficial for the few lesions that do not respond to therapy.
In more widespread, resistant, and recurrent cases, ultraviolet B radiation alone or oral psoralen plus ultraviolet A (PUVA—see Psoriasis : Phototherapy) radiation may be helpful. Occasionally, oral corticosteroids are required, but long-term use should be avoided; a reasonable starting dose is prednisone 40 mg every other day. Corticosteroid alternatives for recalcitrant disease include cyclosporine and methotrexate.
Key Points
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The etiology of nummular dermatitis is unknown, but the disorder is most common in middle-aged and older patients.
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Pruritic discoid lesions form in patches of confluent vesicles and papules that later become dry and lichenified.
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Diagnosis is clinical.
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Treatment includes supportive care (including, eg, corticosteroid cream) for the itching, antibiotics for infection, and ultraviolet light therapy for widespread, resistant, and recurrent lesions.
