What is nummular (discoid) eczema, its causes, prevention, and management?

Nummular Eczema: Definition, Causes, Prevention, and Management

What is Nummular Eczema?

Nummular eczema (also called discoid eczema) is a chronic inflammatory skin condition characterized by sharply defined, coin-shaped (1-10 cm diameter), intensely pruritic, erythematous plaques that are typically multiple and symmetrically distributed, most commonly on the lower and upper extremities. 1 The lesions begin as small red-purplish papules and vesicles that coalesce to form exudative circular patches, which then evolve into eczematous or lichenified discoid plaques. 2

Recent molecular evidence demonstrates that nummular eczema is actually a variant of atopic dermatitis with overlapping type 2 and type 3 immune signatures, though type 2 immunity predominates. 3 The condition typically follows a chronic, relapsing course with significant impact on quality of life, with itching causing the most impairment. 4

Causes and Aggravating Factors

Primary Contributing Factors

• Dry skin (xerosis) is present in two-thirds of patients and represents a fundamental predisposing factor 4
• Atopic predisposition: 14% have personal history of atopic dermatitis, and half have history of atopy or contact dermatitis 4
• Contact allergens: Nickel is the most common allergen identified on patch testing 4
• Dental/focal infections: Latent odontogenic infections detected by panoramic X-ray may be an aggravating factor in treatment-resistant cases 5

Environmental and Behavioral Triggers

• Emotional stress is a significant aggravating factor 4
• Alcohol consumption exacerbates the disease 4
• Seasonal variation: Exacerbation in summer or presence of skin dryness predicts persistent disease 4
• Irritant exposure: Soaps and detergents that remove natural skin lipids worsen the condition 6
• Temperature extremes should be avoided 6

Prevention Strategies

Skin Barrier Protection

• Replace all soaps with dispersible cream cleansers as soap substitutes to prevent lipid stripping 6, 7
• Apply emollients liberally and frequently (at least twice daily) to maintain skin hydration 7
• Apply emollients immediately after bathing when skin is most hydrated to lock in moisture 7

Avoidance Measures

• Wear cotton clothing next to skin; avoid wool or synthetic fabrics that irritate 6, 7
• Keep fingernails short to minimize damage from scratching 6, 7
• Avoid harsh detergents and fabric softeners when washing clothes 7
• Maintain comfortable room temperatures, avoiding excessive heat or cold 7
• Identify and eliminate contact allergens: Consider patch testing in chronic, recalcitrant cases 1, 4
• Address dental infections: Screen with panoramic X-ray in treatment-resistant cases 5

Management Approach

First-Line Treatment

High-potency or ultra-high-potency topical corticosteroids are the mainstay of therapy for nummular eczema. 1 Use the least potent preparation that effectively controls symptoms, with intermittent breaks when possible. 6, 7

Bathing Protocol

• Use lukewarm water for 5-10 minutes to cleanse and hydrate skin 7
• Apply bath oils according to patient preference 6
• Immediately follow with emollients to provide a surface lipid film that retards evaporative water loss 6, 7

Managing Secondary Infection

Watch for signs of bacterial infection (crusting, weeping) or herpes simplex (grouped punched-out erosions, vesiculation). 6

• For suspected Staphylococcus aureus: Use flucloxacillin or cephalexin after obtaining bacterial cultures 7, 8
• For herpes simplex (eczema herpeticum): Initiate systemic acyclovir immediately, as this may progress rapidly to systemic infection without antiviral therapy 8

Adjunctive Therapies

• Sedating antihistamines at night may help with sleep disturbance from itching (non-sedating antihistamines have little value) 7
• Topical calcineurin inhibitors (tacrolimus 0.1% ointment or pimecrolimus 1% cream) can be used as alternatives to corticosteroids, particularly for sensitive areas 6, 7
• Treat identified dental infections: In 11 of 13 cases with odontogenic infections, skin lesions partially or completely improved after dental treatment 5

Targeted Biologic Therapy

Dupilumab (anti-IL-4/IL-13) demonstrates clinical and molecular efficacy in nummular eczema, supporting the predominance of type 2 immunity and making this the primary target for specific therapeutic interventions. 3

Patient Education Essentials

• Demonstrate proper application technique for emollients and medications 6, 7
• Provide written instructions to reinforce verbal teaching 6, 7
• Explain that deterioration may indicate infection or contact dermatitis requiring prompt evaluation 6, 7
• Address corticosteroid fears, as undertreatment from steroid phobia is common 7

Common Pitfalls

• Do not abruptly discontinue high-potency corticosteroids, as this may cause rebound flare 7
• Do not overlook dental infections in treatment-resistant cases 5
• Do not use hot water baths or harsh soaps, which exacerbate dryness 1
• Do not assume dietary restriction is helpful unless working with selected infants under professional supervision 7