Nummular Eczema / Discoid Eczema — Chronic inflammatory skin disease characterized by coin-shaped (nummular), well-defined, erythematous, scaly plaques that are often intensely pruritic.
Etiology & Predisposing Factors
Exact cause is unknown, but multiple factors contribute:
- Skin barrier dysfunction → xerosis (dry skin)
- History of atopic dermatitis or allergic tendencies
- Environmental triggers:
- Cold/dry weather
- Frequent bathing or harsh soaps
- Low humidity
- Secondary factors:
- Stress
- Alcohol use
- Infection (Staph aureus colonization)
- Metal allergy (nickel)
- Medications (diuretics, interferon)
Pathophysiology
Transepidermal water loss → dry skin → inflammation
Scratching worsens barrier damage → chronic eczema
Clinical presentation
- Coin-shaped erythematous plaques (1–10 cm)
- Surface may appear scaly, crusted, or oozing
- Intense itching
- Symmetrical distribution
- Common sites:
- Extremities (legs > arms)
- Dorsal hands
- Trunk (less common)
- Chronic lesions → lichenification, hyperpigmentation
Distinctive Feature: Round/oval lesions with clear margins, resembling fungal infection, but usually multiple plaques and very pruritic.
Investigations
- Clinical evaluation
- KOH test to rule out tinea corporis (important differential)
- Patch testing if allergic trigger suspected
- Biopsy if uncertain (shows spongiotic dermatitis)
Management
Goal: Restore skin barrier & control inflammation.
General Care
- Regular emollients/moisturizers (ointment preferred)
- Avoid irritants (hot showers, harsh soaps)
- Humidify environment
- Avoid scratching
Topical Treatment
- Mid- to high-potency corticosteroids
- Wet dressings for oozing lesions
- Calcineurin inhibitors (tacrolimus/pimecrolimus) for sensitive areas or steroid-sparing
Systemic Treatment (Moderate–Severe)
- Antihistamines for itching
- Short course oral corticosteroids if extensive flare
- Phototherapy (NB-UVB) for chronic or refractory cases
- Treat bacterial superinfection (e.g., mupirocin or systemic antibiotics)
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