Differentiating Eczema from Tinea
Distinguish eczema from tinea primarily by distribution pattern, border characteristics, and presence of scale: eczema typically presents with bilateral symmetrical involvement of flexural areas with ill-defined borders and pruritus, while tinea shows asymmetric annular lesions with raised, scaly, well-demarcated borders.
Key Diagnostic Features
Eczema (Atopic Dermatitis) Characteristics
Clinical presentation requires an itchy skin condition plus three or more of the following 1:
- Bilateral flexural involvement - elbows, neck folds (or cheeks in children under 4 years) 1
- Personal or family history of asthma or hay fever - critical distinguishing feature from fungal infection 1
- General dry skin (xerosis) in the past year - reflects underlying barrier dysfunction 1
- Age-specific distribution: flexures in older children/adults; cheeks, forehead, and outer limbs in children under 4 years 1
- Onset typically in first two years of life (60% by first year, 90% by age 5) 1
- Ill-defined borders with erythema, edema, excoriations, and possible lichenification 1
Tinea Characteristics
Fungal infections present distinctly different morphology 2:
- Asymmetric, unilateral distribution - unlike the bilateral pattern of eczema 3
- Annular (ring-shaped) lesions with raised, scaly, well-demarcated borders and central clearing 2
- Absence of atopic history - no personal/family history of asthma, allergic rhinitis, or atopic diseases 1
- KOH preparation positive for fungal elements - confirms diagnosis when clinical uncertainty exists 3
Critical Diagnostic Algorithm
Step 1: Assess Distribution Pattern
Step 2: Evaluate Border Characteristics
Step 3: Obtain Atopic History
- History of asthma, hay fever, or first-degree relative with atopic disease → eczema 1
- Absence of atopic history → consider tinea or other diagnoses 3
Step 4: Consider Age and Onset
- Onset in first 2 years of life with chronic relapsing course → eczema 1
- New onset at any age without prior atopic history → consider tinea 3
Common Pitfalls to Avoid
Deterioration in previously stable eczema may indicate secondary bacterial infection or development of contact dermatitis, not necessarily treatment failure 1. Look for crusting, weeping, or honey-colored discharge suggesting bacterial superinfection requiring antibiotic coverage 3.
Do not overlook tinea infection in atopic patients - the two conditions can coexist, and fungal infection may trigger or worsen allergic symptoms including asthma and rhinitis 4. If eczema appears unilateral or has unusual features, perform KOH preparation 3.
Eczema herpeticum presents as multiple uniform "punched-out" erosions and requires immediate systemic acyclovir - this is a medical emergency that can be mistaken for bacterial infection 3.
Treatment Approach Based on Diagnosis
For Confirmed Eczema
- Topical corticosteroids are first-line treatment - potency selected based on age, site, and disease extent 1
- Liberal emollient use - apply immediately after 10-15 minute lukewarm baths 1
- Low to medium potency steroids for face/flexures to avoid skin atrophy 1
For Confirmed Tinea
- Topical antifungals (terbinafine) for localized tinea corporis/cruris - cures most ringworm and jock itch 2
- Oral antifungals for tinea capitis or extensive disease - griseofulvin is standard 3
When Diagnosis Uncertain
If doubt exists about the diagnosis, consider KOH preparation before initiating treatment 3. Skin biopsy is generally not helpful for eczema diagnosis but may be needed if cutaneous T-cell lymphoma or other serious conditions are suspected in adults 1.
In patients with both atopic dermatitis and suspected fungal infection, treating the fungal component may dramatically improve allergic symptoms including asthma and rhinitis 4.