Correct Answer: B. Atopic dermatitis La d
Atopic dermatitis (AD) is the most probable diagnosis given the clinical triad of age (adolescent), pruritus, and positive family history of atopy. The patient is 15 years old with itchy lesions and a family history of asthma—both cardinal features of AD. Atopic dermatitis is a chronic inflammatory skin condition characterized by intense pruritus, impaired skin barrier function, and immune dysregulation. The "atopic triad" (asthma, allergic rhinitis, atopic dermatitis) runs in families due to shared genetic predisposition and elevated IgE levels. In Indian populations, AD prevalence is 7–10% in children and adolescents, with peak onset between 2–15 years. The condition presents with erythematous, excoriated, lichenified plaques in flexural areas (antecubital/popliteal fossae, neck, face). The intense pruritus is worse at night and triggered by irritants, stress, and low humidity—particularly relevant in India's dry seasons. Diagnosis is clinical, based on Hanifin & Rajka criteria (3 of 4 major criteria: early onset, pruritus, chronic course, personal/family history of atopy). Management follows the Indian Academy of Dermatology guidelines: emollients as first-line, topical corticosteroids for flares, and allergen avoidance.
Why the other options are wrong
A. Allergic contact dermatitis — Allergic contact dermatitis (ACD) presents with acute, well-demarcated erythema and vesicles in a distribution matching the allergen exposure (e.g., linear streaks from plant contact). It lacks the chronic, pruritic, lichenified morphology and does NOT have a family history of atopy. ACD is triggered by specific contact allergens (nickel, poison ivy, cosmetics), whereas AD is intrinsic and genetically predisposed. The positive family history of asthma strongly favors atopy over contact sensitization. C. Seborrhoeic dermatitis — Seborrhoeic dermatitis is a non-pruritic or mildly pruritic condition affecting sebum-rich areas (scalp, face, chest, intertriginous zones). It presents with yellowish, greasy scales and is NOT associated with intense pruritus or family history of atopy. Seborrhoeic dermatitis is common in infants and older adults, not typically in adolescents without predisposing factors (HIV, Parkinson's). The intense itching and atopic family history rule this out. D. Erysipelas — Erysipelas is an acute, superficial cellulitis caused by Streptococcus pyogenes, presenting with sharply demarcated, bright red, warm, edematous plaques with systemic symptoms (fever, chills, lymphadenopathy). It is an infectious condition, not a chronic inflammatory dermatitis. The absence of fever, acute onset, and systemic signs, combined with the chronic pruritic history and family history of atopy, excludes erysipelas entirely.
High-Yield Facts
- Atopic dermatitis peak onset: 2–15 years; adolescent presentation with family history of asthma is classic.
- Atopic triad: asthma, allergic rhinitis, and atopic dermatitis share genetic predisposition and elevated IgE; family history is a major diagnostic criterion.
- Intense pruritus is the hallmark symptom of AD; 'the itch that rashes' rather than 'the rash that itches'.
- Hanifin & Rajka criteria: diagnosis requires ≥3 of 4 major criteria (early onset, pruritus, chronic course, personal/family history of atopy).
- Flexural distribution in adolescents/adults: antecubital fossae, popliteal fossae, neck, and face are typical sites in older children and teenagers.
- Indian DOC: emollients + topical corticosteroids (Class III–IV for body, Class I–II for face); systemic agents (cyclosporine, dupilumab) for severe cases per IAD guidelines.
Mnemonics
**ITCH (Atopic Dermatitis Red Flags) Intense pruritus (hallmark), Topical steroids (first-line), Chronic course, History of atopy (family/personal). Use this to differentiate AD from other eczemas at the bedside. ATOPY (Genetic Predisposition) Asthma, Topical steroids needed, Often flexural, Pruritus severe, Y**oung onset (2–15 years). Helps recall the atopic triad and typical presentation.
NBE Trap
NBE may pair "contact dermatitis" with "itchy lesions" to trap students who confuse acute allergic contact dermatitis (triggered by specific allergen exposure) with chronic atopic dermatitis (intrinsic genetic condition). The family history of asthma is the discriminator—it points to atopy, not contact sensitization.
Clinical Pearl
In Indian outpatient practice, adolescent girls with "itchy arms" and a mother with asthma are almost always atopic dermatitis—the seasonal exacerbation during dry winters and stress-triggered flares are classic. Emollients (glycerin-based creams) and topical steroids are the backbone; many Indian families mistakenly avoid steroids, worsening disease control.
_Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 25 (Skin); Harrison's Principles of Internal Medicine, Ch. 325 (Atopic Dermatitis); Indian Academy of Dermatology, Venereology & Leprology (IADVL) Guidelines on Atopic Dermatitis Management_