A 6-year-old boy from Delhi presents with intense itching and visible scratching lesions on his face, neck, and flexural surfaces (antecubital and popliteal fossae) for the past 3 months. His mother reports that symptoms worsen in winter and improve during monsoon. On examination, he has lichenification, excoriation, and mild xerosis. His father has a history of allergic rhinitis and his maternal grandmother has asthma. Serum IgE is elevated at 450 IU/mL. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Atopic Dermatitis ### Key Diagnostic Features Present **Key Point:** Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterized by intense pruritus, typical morphology, and a strong genetic/atopic predisposition. This case demonstrates the classic presentation of atopic dermatitis: | Feature | Present in Case | Significance | |---------|-----------------|-------------| | **Age of onset** | 6 years (childhood) | Peak onset 2–5 years; can persist into adulthood | | **Distribution** | Face, neck, flexural surfaces | Pathognomonic flexural pattern in children | | **Pruritus** | Intense, visible scratching | "Itch that scratches" — hallmark symptom | | **Xerosis** | Mild, noted on exam | Impaired skin barrier function | | **Lichenification** | Present | Indicates chronic rubbing and inflammation | | **Seasonal variation** | Worse in winter | Common trigger; dry air exacerbates | | **Family history** | Father: allergic rhinitis; grandmother: asthma | Atopic triad inheritance pattern | | **Elevated IgE** | 450 IU/mL | Supports atopic phenotype (normal <100 IU/mL) | ### Pathophysiology 1. **Genetic predisposition** — mutations in filaggrin (FLG) and other barrier proteins 2. **Impaired skin barrier** — reduced ceramides, increased transepidermal water loss (TEWL) 3. **Immune dysregulation** — Th2-skewed response, elevated IgE, increased IL-4, IL-5 4. **Microbial colonization** — *Staphylococcus aureus* overgrowth in lesional skin ### Diagnostic Criteria (Hanifin & Rajka) **Key Point:** Diagnosis is clinical; no single pathognomonic test exists. At least 3 of 4 major criteria required: - Pruritus - Typical morphology and distribution (flexural in children) - Chronic or relapsing course - Personal or family history of atopy This patient meets all four. ### High-Yield Mnemonic: **SCRATCH** - **S** — Severe pruritus ("itch that scratches") - **C** — Chronic relapsing course - **R** — Recurrent infections (*S. aureus*) - **A** — Atopic family history (asthma, rhinitis, eczema) - **T** — Typical flexural distribution (children) - **C** — Childhood onset (often <5 years) - **H** — Heightened IgE levels ### Clinical Pearl The **"itch-scratch cycle"** is central to AD pathophysiology. Pruritus → scratching → barrier disruption → inflammation → more pruritus. Breaking this cycle (emollients, antihistamines, topical corticosteroids) is key to management.