Atopic Dermatitis
A chronic skin condition causing severely dry, red, itchy patches. Known as 'the itch that rashes,' it mostly affects children but can persist into adulthood.
Emergency Management: Eczema herpeticum requires immediate hospitalization for IV acyclovir (e.g., 5-10 mg/kg IV every 8 hours) and ophthalmology consult if the face is involved, to prevent herpetic keratoconjunctivitis and blindness.
Atopic dermatitis (AD) is a chronic, highly pruritic, inflammatory skin disease that typically begins in childhood. It is characterized by a defective skin barrier and an exaggerated Th2-mediated immune response to environmental allergens, resulting in relapsing eczematous lesions.
Detailed Overview
AD is the cutaneous manifestation of 'atopy', often preceding asthma and allergic rhinitis in the 'atopic march'. A fundamental defect involves mutations in the filaggrin gene, which compromises the stratum corneum, leading to transepidermal water loss and increased penetration of allergens. The intense itching triggers a 'itch-scratch cycle' that further damages the skin, promoting colonization and infection by Staphylococcus aureus. Management requires a dual approach: aggressive barrier restoration and suppression of local inflammation.
Epidemiology & Demographics
Affects up to 20% of children and 1-3% of adults globally. Onset usually occurs before age 5, with many cases presenting within the first 6 months of life.
Etiological Mechanism
A combination of genetic epidermal barrier defects (e.g., null mutations in the FLG gene encoding filaggrin) and dysregulation of the innate and adaptive immune systems, skewed toward Th2 inflammation (IL-4, IL-13, IL-31).
Primary Causes
Triggered by environmental factors (harsh soaps, dry winter weather, wool clothing), psychological stress, and exposure to specific allergens (dust mites, pet dander) acting on a genetically susceptible barrier.
Filaggrin deficiency causes a leaky epidermal barrier. Antigens penetrate the skin and are captured by Langerhans cells, which migrate to lymph nodes and stimulate naive T cells into Th2 cells. Th2 cells migrate back to the skin, releasing IL-4 and IL-13 (which further inhibit filaggrin production, worsening the barrier) and IL-31 (the 'itch cytokine' that directly stimulates cutaneous sensory nerves). The scratched skin bleeds, excoriates, and releases damage-associated molecular patterns (DAMPs) that sustain chronic inflammation (lichenification).
Diagnostic Criteria & Guidelines
Clinical diagnosis based on the Hanifin and Rajka criteria or UK Working Party criteria: requires an itchy skin condition plus 3 or more of: 1) history of flexural involvement, 2) history of asthma/hay fever, 3) history of generalized dry skin, 4) onset before age 2, and 5) visible flexural dermatitis.
Barrier repair is paramount: thick emollients (ointments like petroleum jelly or heavy creams) applied immediately after a lukewarm bath (soak-and-seal technique). Topical Corticosteroids (TCS) for flares: Hydrocortisone 2.5% for face/folds, Triamcinolone acetonide 0.1% ointment twice daily for body trunk/extremities for 1-2 weeks.
Second-Line & Adjunctive Therapy
Topical Calcineurin Inhibitors (Tacrolimus 0.1% ointment) or PDE4 inhibitors (Crisaborole 2% ointment) for face/eyelids to avoid steroid atrophy. For severe, recalcitrant systemic disease: Dupilumab (anti-IL-4Rα biologic) 600 mg SQ induction then 300 mg SQ every 2 weeks, or oral JAK inhibitors (e.g., Upadacitinib 15 mg PO daily).
Surgical & Procedural Management
Not applicable.
Patient Counseling & Advice
Reassure parents that while steroids have a bad reputation ('steroid phobia'), short bursts of appropriate-strength topical steroids are incredibly safe and necessary to prevent misery and infection.
Follow-Up & Monitoring Schedule
Assess control using tools like EASI (Eczema Area and Severity Index). Monitor patients on chronic topical steroids for skin atrophy, striae, and telangiectasias.
Preventive Strategies
Daily, relentless moisturization of high-risk infants starting from birth may delay or prevent the onset of clinical eczema.
Approximately 60-70% of children outgrow their severe symptoms by early adolescence. However, many retain dry, sensitive skin for life, and a subset experiences severe, lifelong disease.