A 4-year-old boy from Delhi presents with intense pruritus and sleep disturbance for the past 6 months. His mother reports that the itching worsens in winter and improves during monsoon. On examination, he has lichenified plaques on the flexural surfaces of elbows and knees, with excoriations and a dry, rough skin texture. His serum IgE is elevated at 850 IU/mL. He has a personal history of allergic rhinitis and a family history of asthma in his father. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Atopic Dermatitis ### Key Clinical Features Presented **Key Point:** This case demonstrates the classic triad of atopic dermatitis: pruritus, lichenification on flexural surfaces, and personal/family history of atopy. ### Diagnostic Criteria (Hanifin & Rajka) The patient meets multiple major criteria: | Feature | Present in Case | Significance | |---------|-----------------|---------------| | Pruritus (essential) | Yes — intense, sleep-disturbing | Hallmark symptom | | Flexural distribution | Yes — elbows, knees | Classic pattern in children | | Chronic/relapsing course | Yes — 6 months | Typical timeline | | Personal history of atopy | Yes — allergic rhinitis | Atopic syndrome | | Family history of atopy | Yes — father's asthma | Genetic predisposition | | Elevated serum IgE | Yes — 850 IU/mL | Supports diagnosis | | Lichenification & excoriations | Yes — visible on exam | Chronic scratching | **High-Yield:** At least 3 major criteria are required for diagnosis; this patient has ≥5. ### Pathophysiology 1. **Genetic predisposition** — filaggrin mutations (FLG) impair skin barrier function 2. **Impaired barrier** — transepidermal water loss (TEWL) ↑, increased susceptibility to irritants 3. **Immune dysregulation** — Th2-skewed response, elevated IL-4, IL-5, IL-13 → IgE production 4. **Chronic inflammation** — eosinophil infiltration, mast cell activation → pruritus **Mnemonic: SCRATCH** — **S**ensitivity to irritants, **C**hronic relapsing, **R**aised IgE, **A**topy family history, **T**opical steroids responsive, **C**hildhood onset, **H**istory of pruritus ### Seasonal Variation **Clinical Pearl:** Winter exacerbation is typical due to low humidity and increased TEWL; monsoon improvement reflects higher humidity and reduced irritant exposure. ### Investigations Supporting Diagnosis - **Serum IgE:** Elevated in ~80% of moderate-to-severe AD - **Skin prick testing:** May show multiple allergen sensitization (but not diagnostic) - **Histology (if needed):** Spongiosis, acanthosis, perivascular lymphocytic infiltrate **High-Yield:** Elevated IgE alone is NOT diagnostic; clinical presentation + criteria are primary. ### Management Approach ```mermaid flowchart TD A[Atopic Dermatitis Confirmed]:::outcome --> B[Assess Severity]:::decision B -->|Mild| C[Emollients + Topical corticosteroids]:::action B -->|Moderate-Severe| D[Potent TCS + Calcineurin inhibitors]:::action D --> E{Inadequate control?}:::decision E -->|Yes| F[Systemic therapy: Dupilumab, JAK inhibitors]:::action E -->|No| G[Maintenance + Trigger avoidance]:::action A --> H[Educate on barrier repair]:::action ``` **Key Point:** First-line treatment is emollients + topical corticosteroids; systemic agents reserved for moderate-to-severe refractory disease.