Discoid Eczema Clinical Overview
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: This is a common diagnosis in our primary care clinics and dermatology referrals. It is frequently misdiagnosed as kurap (tinea corporis) by patients and junior doctors, leading to inappropriate treatment with antifungals and delayed relief for the patient.
High-Yield Definition: Nummular eczema is a chronic inflammatory skin condition characterized by the presence of pruritic, well-demarcated, coin-shaped (i.e., "nummular") eczematous plaques. (Source: UpToDate).
Clinical One-Liner: It's the intensely itchy, coin-shaped rash that looks like ringworm but isn't.
II. Etiology & Risk Factors
Etiology: The exact cause is unknown. It is not contagious. It represents a pattern of reaction to various triggers on a background of skin barrier dysfunction.
Risk Factors:
Xerosis (Dry Skin): The single most important factor. Common in older adults.
Age: Predominantly affects middle-aged and elderly men.
Skin Trauma: Koebner phenomenon (lesions appearing at sites of minor injury).
Venous Stasis/Varicose Veins: Particularly for lesions on the lower legs.
Contact Sensitivity: Notably to nickel, cobalt, and chromate.
Medications: Can be triggered by drugs like interferon and diuretics.
III. Quick Pathophysiology
Think of it as a localized failure of the skin barrier. Severe xerosis compromises the epidermal barrier, increasing transepidermal water loss. This allows allergens and irritants to penetrate the epidermis, triggering a robust localized T-cell mediated inflammatory response. Staphylococcus aureus frequently colonizes these lesions and its toxins can act as superantigens, further driving inflammation and causing the characteristic exudative, crusted appearance.
IV. Classification
There isn't a formal staging system. We classify lesions clinically based on their morphology, which reflects their acuity:
Acute/Exudative: Vesicular, papular, and intensely erythematous plaques with weeping and serous crusting.
Chronic/Dry: Drier plaques with scaling, lichenification (thickened skin markings), and post-inflammatory pigmentary changes.
V. Clinical Assessment
🚩 Red Flags & Immediate Actions
Rapidly expanding erythema with fever, pain, and warmth: Suggests superimposed cellulitis.
Action: Draw blood for FBC, RP, CRP. Perform a wound swab for C&S. Start empirical IV antibiotics (e.g., Cloxacillin) and admit.
Widespread, confluent rash approaching erythroderma (>90% body surface area): A dermatological emergency.
Action: Immediate hospital admission for stabilisation and urgent dermatology consult.
History
Key Diagnostic Clues: Sudden onset of intensely pruritic, distinct, round-to-oval plaques. The itch is often severe and paroxysmal, frequently disturbing sleep.
Symptom Breakdown:
Common (>50%): Severe pruritus, coin-shaped erythematous plaques, oozing/crusting (acute phase), scaling (chronic phase), lesions on lower legs, symmetrical distribution.
Less Common (10-50%): Lesions on the trunk, hands, or upper extremities.
Pertinent Negatives:
No central clearing (unlike tinea corporis).
No thick, silvery scales (unlike psoriasis).
No burrows or tracking (unlike scabies).
No relevant travel or animal contact history.
Physical Examination (OSCE Approach)
General Inspection: Patient may be distressed due to itch, evidence of scratching (excoriations). Note the distribution of lesions.
Vitals: Afebrile and haemodynamically stable unless a secondary infection is present.
Disease-Specific Examination (Skin):
Look (Inspection):
Morphology: Multiple, well-demarcated, round or oval ("coin-shaped") plaques, typically 1-5 cm in diameter.
Acute Lesions: Appear as collections of small papules and vesicles on an erythematous base, which coalesce into weeping, crusted plaques.
Chronic Lesions: Present as dry, scaly plaques with prominent lichenification. Post-inflammatory hyperpigmentation is common, especially in skin of colour.
Distribution: Classically on the extensor surfaces of the limbs, particularly the shins and dorsum of the hands. The trunk can also be involved. Usually symmetrical.
Pertinent Negatives on Examination: Absence of nail pitting or onycholysis (psoriasis). Absence of lesions in the scalp, intergluteal cleft.
Examination for Differentials: Scrape the edge of a lesion with a scalpel blade for KOH microscopy to rule out fungus. Examine elbows, knees, and scalp for signs of psoriasis.
Clinical Pearl: When an elderly man complains of an intensely itchy "ringworm" on his shins that hasn't cleared with antifungal cream, your top differential must be discoid eczema.
VI. Diagnostic Workflow
This is primarily a clinical diagnosis. Investigations are to exclude differentials.
Differential Diagnosis:
Tinea Corporis:
Points For: Annular (ring-shaped) plaque.
Points Against: Less itchy, shows central clearing, has a raised, scaling advancing edge.
How to Differentiate: Skin scraping for KOH microscopy will be positive for fungal hyphae.
Plaque Psoriasis:
Points For: Well-demarcated erythematous plaque.
Points Against: Has thick, silvery scales which bleed on removal (Auspitz's sign), is typically less pruritic, involves classic sites (scalp, nails, extensors).
How to Differentiate: Clinical features (nail/joint involvement) and skin biopsy if needed.
Allergic Contact Dermatitis:
Points For: Eczematous reaction.
Points Against: Geometrical or bizarre shape corresponding to an external allergen (e.g., rash under a watch strap).
How to Differentiate: History and patch testing.
Investigations Plan:
Bedside / Initial: Skin scraping for KOH microscopy to rule out dermatophytosis.
First-Line Labs: Generally not needed. If secondary infection is suspected, send a swab from a weeping lesion for bacterial culture and sensitivity.
Confirmatory / Gold Standard: A skin punch biopsy is the definitive test if the diagnosis is uncertain. Histopathology will show features of subacute or chronic spongiotic dermatitis.
VII. Staging & Severity Assessment
Severity is not formally staged. It is a clinical assessment based on:
Extent: Body surface area involved.
Symptom burden: Intensity of pruritus and its impact on quality of life (e.g., sleep).
Morphology: Degree of erythema, vesiculation, and lichenification.
VIII. Management Plan
A. Principle of Management:
Restore the skin barrier.
Suppress inflammation and pruritus.
Treat or prevent secondary infection.
Educate the patient to prevent recurrence.
B. Immediate Stabilisation (The ABCDE Plan):
Not applicable for this condition unless the patient presents with complications like severe, widespread secondary infection or erythroderma.
C. Definitive Treatment (The Clinic Plan):
1. Skin Barrier Repair (Non-negotiable first step):
Emollients: Frequent (at least 2-3 times daily) and liberal application of a bland emollient (e.g., emulsifying ointment, white soft paraffin). This is the cornerstone of all eczema management. Counsel the patient to apply after bathing on damp skin.
Lifestyle: Avoid harsh soaps and long, hot showers. Use soap substitutes.
2. Topical Anti-inflammatory Therapy (First-Line):
Topical Corticosteroids: High potency is usually required to control flares.
Drug/Dose: Betamethasone valerate 0.1% cream/ointment or Mometasone furoate 0.1% ointment, applied thinly once daily for 2-4 weeks.
Plan: Once inflammation subsides, taper the frequency or switch to a lower potency steroid to minimise side effects like skin atrophy.
3. Symptom Control:
Antihistamines: A sedating antihistamine (e.g., hydroxyzine 10-25mg or chlorpheniramine 4mg) at night can help break the itch-scratch cycle and aid sleep. Non-sedating antihistamines are less effective as the itch is not primarily histamine-mediated.
4. Management of Secondary Infection:
For localised crusting/weeping: Topical antibiotic (e.g., Fucidin cream).
For more extensive infection: An oral anti-staphylococcal antibiotic (e.g., Cloxacillin 500mg QID for 7 days).
5. For Refractory Disease (Refer to Dermatology):
Topical calcineurin inhibitors (e.g., tacrolimus 0.1% ointment).
Phototherapy (Narrowband UVB).
Systemic agents (oral steroids, methotrexate, azathioprine).
D. Long-Term & Discharge Plan:
Emphasise the chronic, relapsing nature of the condition.
The goal is control, not cure.
Provide a written action plan: use emollients daily, use steroids for flares.
Schedule a follow-up appointment in 2-4 weeks to assess response.
IX. Complications
Immediate: Secondary bacterial infection (S. aureus). Action: Swab and treat with appropriate antibiotics.
Short-Term: Post-inflammatory hyper- or hypopigmentation. Action: Reassure the patient this will fade over many months. Sun protection is advised.
Long-Term: Lichenification from chronic scratching. Skin atrophy, striae, or telangiectasias from improper long-term use of potent topical steroids. Action: Patient education on correct steroid application ("fingertip unit") and tapering.
X. Prognosis
The condition follows a chronic relapsing and remitting course. It can persist for years, but the prognosis is excellent in that it is not life-threatening. Morbidity is related to the intense pruritus and its impact on quality of life. Good control is achievable with consistent adherence to treatment, especially emollient use.
XI. How to Present to Your Senior
Use the SBAR format. Be concise and direct.
(Situation): "Dr, for your review, this is Mr. Tan, a 65-year-old gentleman presenting with a 3-week history of intensely itchy rashes on his legs."
(Background): "He has a background of dry skin. He was treated with a topical antifungal by a GP with no improvement. He has no other significant medical history."
(Assessment): "On examination, he has multiple, well-demarcated, coin-shaped, erythematous plaques with some weeping and crusting on both shins, consistent with discoid eczema. There are no signs of cellulitis. My main differential is discoid eczema; I have sent a skin scraping to rule out tinea."
(Recommendation): "My plan is to start him on frequent emollients, once-daily potent topical betamethasone for two weeks, and hydroxyzine at night for the pruritus. I would like your opinion on this plan."
XII. Summary & Further Reading
Top 3 Takeaways:
Discoid eczema = itchy, coin-shaped plaques. Think of it in older patients with dry skin.
Management is simple but requires consistency: potent topical steroids for flares + liberal emollients always.
Always do a KOH skin scraping if you are even slightly unsure, to definitively rule out tinea.
Key Resources:
UpToDate: Search for "Nummular eczema".
Amboss: Search for "Nummular eczema".
StatPearls: Nummular Eczema.
