Eczema Study Guide

📖 Core Concepts Dermatitis / Eczema – Inflammatory skin conditions marked by itch, redness, and rash; “eczema” usually refers to atopic dermatitis (the most common form). Atopic Dermatitis (AD) – Chronic, hereditary, allergic skin disease that often starts in childhood; linked to asthma and filaggrin gene defects. Contact Dermatitis – Skin reaction to an external substance: allergic (delayed‑type hypersensitivity) or irritant (direct damage). Seborrhoeic Dermatitis – Scaly eruption of scalp, face, or trunk; closely related to dandruff and driven by Malassezia yeast. Skin Barrier – The outermost layer that keeps moisture in and irritants out; dysfunction (e.g., low filaggrin, lipid deficits) underlies AD flares. Treatment Goal – Control inflammation, relieve pruritus, and restore barrier; no cure exists for most types. 📌 Must Remember Epidemiology: 10 % of U.S. population; 20 % of UK children; >60 % of children remit by adolescence. Risk Factors: Filaggrin gene mutations, family history of eczema/food allergy, urban living, hygiene‑hypothesis exposure deficit. Key Tests: Clinical exam + history = primary diagnosis. Patch testing → identify allergic contact agents. Skin biopsy only when diagnosis is uncertain. Topical Steroid Potency Ladder: Weak (hydrocortisone) → mild‑moderate disease. Mid‑potency (triamcinolone) → moderate disease. High‑potency (clobetasol) → severe disease, short‑term only. TCI Preference: Tacrolimus 0.1 % ≈ mid‑potency steroid, more effective than pimecrolimus. Biologic Landmark: Dupilumab (IL‑4Rα blocker) FDA‑approved 2017/2019 for moderate‑severe AD. JAK Inhibitor: Ruxolitinib cream FDA‑approved Sep 2021 for mild‑moderate AD. Phototherapy: Narrowband UVB (NB‑UVB) is the most evidence‑based light treatment; excess UV → skin cancer risk. Complication Alert: Eczema vaccinatum (fatal) after smallpox vaccine; increased bacterial/viral skin infections. 🔄 Key Processes Diagnosing Dermatitis Take detailed history (onset, triggers, family atopy). Perform full skin exam; note distribution & morphology. Order patch test if contact allergy suspected. Consider biopsy only for atypical lesions. Stepwise Management Escalation Step 1: Emollient/moisturizer + gentle cleanser. Step 2: Low‑potency topical steroid (hydrocortisone) for mild flares. Step 3: Mid‑potency steroid or tacrolimus/pimecrolimus if Step 2 inadequate. Step 4: High‑potency steroid (short course) or phototherapy (NB‑UVB). Step 5: Systemic agents (cyclosporine, methotrexate, azathioprine) or biologic (dupilumab). Step 6: Adjuncts (bleach baths for infection, JAK inhibitor cream). Moisturizer Application Routine Cleanse with mild soap → pat dry → apply thick emollient within 3 min of bathing (the “wet‑wrap” principle). Patch Test Procedure Apply suspected allergens on the back under occlusion for 48 h. Read at 48 h (early) and 72–96 h (delayed) for reactions. 🔍 Key Comparisons Allergic vs Irritant Contact Dermatitis Allergic: delayed hypersensitivity, requires prior sensitization, patch test positive. Irritant: immediate damage, no sensitization, often from detergents/water. Topical Steroid vs Topical Calcineurin Inhibitor (TCI) Steroid: rapid anti‑inflammatory; risk of skin atrophy, telangiectasia with prolonged use. TCI: steroid‑sparing; no atrophy; slightly less potent, useful on face/neck. Dupilumab vs Systemic Immunosuppressants Dupilumab: targeted IL‑4/IL‑13 blockade, fewer systemic toxicities, subcutaneous injection. Cyclosporine/Azathioprine: broad immunosuppression, require labs for nephrotoxicity, hypertension, liver toxicity. NB‑UVB Phototherapy vs Broadband UVB NB‑UVB: narrower wavelength (311 nm), higher efficacy, better safety profile. Broadband: less studied, more risk of erythema and long‑term skin cancer. ⚠️ Common Misunderstandings “Moisturizers prevent eczema.” – Regular emollients improve barrier and reduce flares, but they do not prevent the disease in all infants. “All antihistamines control itching in eczema.” – Sedating antihistamines may aid sleep; second‑generation agents show minimal itch relief. “Topical steroids can be used indefinitely.” – Long‑term use leads to skin thinning and other adverse effects; tapering is recommended. “Dupilumab cures eczema.” – It markedly improves disease severity but does not eradicate the underlying atopic predisposition. “All patients need bleach baths.” – Bleach baths are reserved for infected or heavily colonized eczema, not routine use. 🧠 Mental Models / Intuition “Barrier‑First” Model: Think of skin like a brick wall; the “bricks” (corneocytes) need “mortar” (lipids/filaggrin). If mortar is weak → cracks → allergens/irritants penetrate → inflammation. “Potency Ladder” Analogy: Treat AD like climbing a ladder—start at the bottom (emollient), step up only as needed; always aim to step back down once control is achieved. “Trigger‑Response Loop”: Identify a trigger → remove/avoid → break the loop, preventing the downstream immune cascade. 🚩 Exceptions & Edge Cases Infant Cradle‑Cap – Thick yellowish scalp scaling; treat with gentle cleansing and low‑potency topical steroids, not typical AD regimen. Eczema Vaccinatum – Smallpox vaccine contraindicated in any active eczema patient, regardless of severity. Food Allergy Misdiagnosis: Eczema patients are often incorrectly labeled as food‑allergic; confirm with oral food challenge before elimination diets. Steroid‑Responsive vs Steroid‑Resistant: Some chronic AD cases may not respond to even high‑potency steroids, necessitating early escalation to TCIs or biologics. 📍 When to Use Which Moisturizer Type: Oil‑based > water‑based for children; avoid fragrances and known allergens. Topical Steroid Choice: Mild flare, thin skin → hydrocortisone 1 % (weak). Moderate disease, flexural areas → triamcinolone acetonide (mid). Severe, thick plaques → clobetasol propionate (high) – short course only. TCI vs Steroid: Use TCIs on face, neck, intertriginous zones, or when steroid‑phobia/atrophy risk is high. Phototherapy: Reserve NB‑UVB for patients uncontrolled on topical regimen but without contraindications to UV exposure. Systemic Therapy: Indicated for ≥ 30 % BSA involvement or significant QoL impact after failure of topical + phototherapy. Choose cyclosporine for rapid control; consider dupilumab for long‑term safety. JAK Inhibitor Cream: For mild‑moderate AD that is refractory to steroids/TCIs and where systemic therapy is not yet justified. 👀 Patterns to Recognize Flexural Distribution + Dry, Lichenified Skin → classic atopic dermatitis. Sharp, Linear Erythema on Hands/Forearms → allergic contact dermatitis (often nickel, poison ivy). Greasy Scale on Scalp + Eyebrows → seborrhoeic dermatitis. Clustered Vesicles on Extensor Surfaces (elbows/knees) → dermatitis herpetiformis (gluten‑related). Sudden worsening after new detergent or glove use → irritant contact dermatitis. 🗂️ Exam Traps “Emollients prevent eczema in all infants.” – Over‑statement; evidence shows modest risk reduction, not absolute prevention. “Second‑generation antihistamines are first‑line for AD itch.” – They have limited efficacy; sedating antihistamines are only for sleep aid. “All contact dermatitis is allergic.” – Ignoring irritant type leads to missed occupational exposures. “High‑potency steroids are safe for long‑term facial use.” – Will cause atrophy; TCIs are preferred on the face. “Dupilumab works by suppressing the whole immune system.” – It is a targeted IL‑4/IL‑13 pathway blocker, not broad immunosuppression. --- Keep this guide handy; focus on the “Barrier‑First” approach, the stepwise treatment ladder, and recognizing distribution patterns to ace your exam.