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Plate 10

Nummular Dermatitis

Also called: Discoid eczema · Nummular eczema

Eczema & dermatitis
Illustration © Roxana Barin Click to enlarge

General information

  • Inflammatory dermatitis characterized by round or oval, “coin-shaped” eczematous plaques with prominent pruritus.
  • Acute lesions may be papulovesicular, oozing, and crusted.
  • More common in adults, particularly middle-aged and older adults.
  • Often worsens during cold, dry seasons (fall and winter).
  • Xerosis (dry skin) is common.
  • An atopic background may be present but is not required.
  • May follow a chronic or relapsing course.

Symptoms / presentation

  • Development of round, intensely pruritic plaques.
  • Pruritus may be severe and lead to secondary excoriations.
  • Flares are often associated with dry skin, particularly during winter.
  • Lesions may initially be oozing and subsequently become scaly and thickened.

Clinical exam

  • Well-demarcated, round or oval erythematous plaques.
  • Characteristic “coin-shaped” appearance.
  • Papules and small vesicles may coalesce into plaques.
  • Borders may appear more prominent than the center.
  • Acute phase: oozing ± crusting.
  • Chronic phase: scaling, excoriations ± lichenification.
  • Yellow crusting, pustules, or purulent drainage may indicate secondary bacterial infection.

Distribution

  • Legs +++, particularly the lower legs.
  • Arms and forearms.
  • Trunk.
  • Lesions may be multiple and bilateral.
  • Face and scalp are generally spared.

Dermoscopy

  • Erythematous background.
  • White to yellow scales.
  • Yellowish serous crusts may be present in exudative lesions.
  • Dotted vessels may be present, usually with an irregular distribution.
  • Dermoscopy may help differentiate nummular eczema from psoriasis and dermatophytosis.

Diagnosis

  • Primarily a clinical diagnosis.
  • KOH preparation ± fungal culture if dermatophytosis is suspected.
  • Patch testing if allergic contact dermatitis is suspected or disease is persistent/recurrent.
  • Bacterial culture if secondary infection is suspected.
  • Skin biopsy is rarely required but may be considered for atypical or persistent lesions.

Differential diagnosis

Treatment plan

  • Frequent and generous use of emollients, particularly after bathing.
  • Minimize hot showers, harsh soaps, frequent washing, and other skin irritants.
  • Topical corticosteroids of appropriate potency are first-line for active lesions.
  • Clobetasol propionate 0.05% once or twice daily for 7–14 days may be used for thick plaques on the trunk or extremities.
  • Betamethasone dipropionate 0.05% once or twice daily for 1–2 weeks, depending on formulation and location.
  • Wet compresses may be useful for acute, exudative lesions.
  • Antibiotics only when clinical bacterial infection is present.
  • Extensive or refractory disease: narrowband UVB phototherapy or specialist-directed systemic therapy may be considered.
  • Identify and avoid relevant irritants, triggers, and contact allergens.

References

  1. DermNet — Discoid eczema (nummular dermatitis)
  2. American Academy of Dermatology (AAD) — Nummular eczema
  3. UpToDate — Nummular dermatitis
  4. Bolognia JL, Schaffer JV, Cerroni L. Dermatology. Elsevier.