Definition
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Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin condition associated with pruritus, dry skin, and eczema, often linked to atopy (asthma, allergic rhinitis).
Epidemiology & Risk Factors
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Prevalence: 10–20% in children, 2–5% in adults.
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Most cases begin before age 5.
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Family history of atopy increases risk.
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Triggers: irritants (soap, detergents), allergens, stress, infections (Staphylococcus aureus).
Pathophysiology
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Skin barrier dysfunction → increased transepidermal water loss.
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Immune dysregulation → Th2-dominant inflammation.
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Pruritus-scratch cycle → worsens lesions.
Clinical Features
| Feature | Children | Adults |
|---|---|---|
| Distribution | Face, scalp, extensor surfaces | Flexural areas (elbows, knees), hands, eyelids |
| Appearance | Red, weeping, crusted lesions | Lichenified, dry plaques |
| Pruritus | Severe, often nocturnal | Persistent, scratching → lichenification |
| Associated signs | Dennie-Morgan folds, keratosis pilaris | Chronic lichenification, pigment changes |
💡 Exam Tip: Chronic scratching → thickened, leathery skin (lichenification).
Differential Diagnosis
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Contact dermatitis (allergic or irritant) – usually confined to exposed areas, history of contact.
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Seborrheic dermatitis – scalp, nasolabial folds, greasy scales.
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Psoriasis – well-demarcated plaques with silvery scales, extensor surfaces.
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Scabies – intense nocturnal itch, burrows in web spaces.
Investigations
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Usually clinical diagnosis.
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Consider skin swab if superimposed infection suspected (commonly Staph aureus).
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Allergy testing in selected chronic cases.
Management
General Measures
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Avoid triggers: soaps, harsh detergents, allergens.
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Emollients liberally and regularly.
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Short nails to reduce trauma from scratching.
Topical Therapy
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Mild–moderate: topical corticosteroids (low–medium potency).
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Severe or resistant: topical calcineurin inhibitors (tacrolimus, pimecrolimus).
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Wet wrap therapy for acute flares.
Systemic Therapy
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Severe/refractory cases: oral corticosteroids (short-term), cyclosporine, methotrexate, or biologics (dupilumab).
Infection Management
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Secondary bacterial infection: flucloxacillin (Staph aureus) if purulent/crusted.
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HSV infection: consider acyclovir if eczema herpeticum suspected.
Complications
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Secondary infection: Staphylococcus aureus, herpes simplex (eczema herpeticum).
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Sleep disturbance, poor quality of life.
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Chronic lichenification and pigment changes.
PLAB-Style Questions
Q1: A 4-year-old boy presents with itchy, red, crusted lesions on his cheeks and extensor surfaces. His mother has a history of asthma. Most likely diagnosis?
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A. Psoriasis
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B. Atopic dermatitis
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C. Seborrheic dermatitis
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D. Contact dermatitis
✅ Answer: B. Atopic dermatitis
(Early childhood onset, atopic family history, extensor distribution).
Q2: An adult woman has chronic itchy plaques in her elbow and knee folds. She uses emollients irregularly. What is the first-line treatment?
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A. Oral corticosteroids
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B. Topical calcineurin inhibitors
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C. Topical corticosteroids
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D. Phototherapy
✅ Answer: C. Topical corticosteroids
(Flexural lichenified eczema → topical corticosteroids first-line, adjunct emollients).
High-Yield Pearls
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Flexural involvement in adults, extensor in children.
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Atopy triad: eczema, asthma, allergic rhinitis.
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Pruritus-scratch cycle → lichenification.
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Topical corticosteroids + emollients = cornerstone therapy.
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Watch for secondary infection (Staph aureus, HSV).
