Atopic Dermatitis

Atopic Dermatitis: Definition & Epidemiology - Itchy Beginnings

• Definition: A chronic, relapsing, intensely pruritic inflammatory skin condition.
• Epidemiology:
  • Common in childhood; often begins in infancy (first 6 months).
  • Global prevalence: 10-20% in children, 1-3% in adults.
  • Indian studies show childhood prevalence ranging from 2.7% to over 20% in different regions.
  • Strongly linked to personal or family history of atopy (asthma, allergic rhinitis).
  • Often the initial step in the 'atopic march'.

⭐ Atopic dermatitis is often the first manifestation of the 'atopic march' (eczema → allergic rhinitis → asthma).

Atopic Dermatitis: Pathophysiology - Barrier Breakdown

• Genetic Factors:
  • Key: Filaggrin (FLG) gene mutations impair skin barrier protein formation.
  • Other susceptibility loci also contribute.
• Immune Dysregulation:
  • Dominant Th2 immune response (e.g., IL-4, IL-13, IL-31).
  • Results in ↑ IgE production by B-cells.
  • Eosinophilia often present.
• Epidermal Barrier Dysfunction:
  • ↓ Ceramides & other lipids, weakening intercellular matrix.
  • ↑ Transepidermal Water Loss (TEWL), leading to xerosis.
  • Impaired barrier allows easier allergen/microbe penetration.

⭐ Mutations in the filaggrin (FLG) gene are a major predisposing factor for atopic dermatitis, leading to impaired skin barrier function.

Atopic Dermatitis: Clinical Manifestations - The Eczema Map

• Pruritus: Cardinal symptom; often paroxysmal, worse at night.

• Age-Dependent Presentation:

  Age Group	Morphology	Distribution
  Infantile (0-2 yrs)	Vesicles, papules, oozing, crusting; acute	Face (cheeks, forehead, chin), scalp, extensor surfaces; spares diaper area. 📌 Face, Extensors, Scalp (FES)
  Childhood (2-12 yrs)	Lichenified plaques, papules; subacute/chronic	Flexural areas (antecubital, popliteal fossae), wrists, ankles, neck.
  Adult (>12 yrs)	Lichenification, dry, fissured skin; chronic	Flexures, hands, face (periorbital, perioral), neck, upper trunk.

• Associated Features:

  • Xerosis (dry skin) - universal.
  • Dennie-Morgan folds (infraorbital folds).
  • Hertoghe's sign (thinning/loss of lateral eyebrows).
  • Keratosis pilaris (follicular papules, upper arms, thighs).
  • Pityriasis alba (hypopigmented patches, face, neck).

⭐ Infantile atopic dermatitis typically affects the face (cheeks, forehead, chin) and extensor surfaces, characteristically sparing the diaper area.

Atopic Dermatitis: Diagnosis & Management - Soothe & Control

• Diagnosis:

  • Hanifin & Rajka criteria: Pruritus + ≥3 major/minor criteria.
    • Major: Typical morphology/distribution (flexural adult; facial/extensor infant), personal/family history of atopy, chronic/relapsing dermatitis.
    • Minor: Xerosis, ichthyosis/palmar hyperlinearity/keratosis pilaris, Dennie-Morgan infraorbital fold, ↑serum IgE, early age of onset.
  • DDx: Seborrheic dermatitis, contact dermatitis, psoriasis, scabies.

• Management: Stepwise approach.

  • Baseline: Emollients (liberal, frequent), trigger avoidance (irritants, allergens).

  ⭐ Emollients are the cornerstone of atopic dermatitis management, used liberally and frequently even during remission to maintain skin barrier function.

  • Mild AD: Low-potency Topical Corticosteroids (TCS) (e.g., hydrocortisone 1%). Topical Calcineurin Inhibitors (TCIs) (e.g., tacrolimus 0.03%, pimecrolimus) for sensitive areas/long-term.
  • Moderate AD: Medium-potency TCS (e.g., betamethasone valerate 0.1%). TCIs. Antihistamines for pruritus. Wet wraps for acute flares.
  • Severe AD: High-potency TCS (e.g., clobetasol propionate 0.05%). Phototherapy (NB-UVB). Systemic therapy: cyclosporine (3-5 mg/kg/day), azathioprine, methotrexate, biologics (e.g., Dupilumab).

• Complications:
  • Eczema herpeticum (HSV superinfection) ⚠️ Medical emergency.
  • Impetiginization (bacterial superinfection, e.g., Staph. aureus).
  • Erythroderma.

High‑Yield Points - ⚡ Biggest Takeaways

• Type I Hypersensitivity; strong family history of atopy (asthma, allergic rhinitis).
• Classic distribution: Infants (cheeks, extensors), Children/Adults (flexures like antecubital/popliteal fossae).
• Intense pruritus is hallmark, driving the itch-scratch cycle.
• Key features: xerosis (dry skin), lichenification (from chronic scratching).
• Filaggrin (FLG) gene mutations are a major predisposing factor, impairing skin barrier.
• Diagnosis is clinical; Hanifin and Rajka criteria are often used (major & minor).
• Management cornerstones: emollients, topical corticosteroids or calcineurin inhibitors, and trigger avoidance.