Definition (J Allergy Clin Immunol 2006;118:152)
• Chronic, immune-mediated, inflammatory, pruritic skin dz occurring in pts w/ atopic diathesis, w/ variable clinical pattern depending on age
Pathophysiology (J Invest Dermatol 2012;132:949)
• Impaired epidermal barrier: Stratum corneum defects → ↓ epidermal water content
• Mutations in the filaggrin gene predispose to AD (filaggrin is a protein in the stratum corneum that helps maintain hydration and has anti-staph properties)
• Dry skin → pruritis and scratching → trauma and inflammation
• Water loss → changes in epidermal lipids → cracks in the stratum corneum
• Antigenic and irritant agents penetrate the skin and activate immune cells
• Immune dysfunction w/ exaggerated Th2 response: IgE prod, eosinophilia, and proinflammatory cytokines → hyperactive immune response → extravasation of inflammatory cells, cellular signaling at injury site
• Pruritus mechanism not just 2/2 histamine
• Triggers: Stress-induced immunomodulation, food + inhalant allergens, chemical irritants, skin infection, hot/humid or cold/dry weather, viral infections esp w/ fever
Epidemiology (N Engl J Med 2008;358:1483, N Engl J Med 2005;352:2314)
• Affects 15–30% of children and 2–10% of adults
• Age of onset: 45% in 1st 6 mo of life, 60% before age 1; 85% before age 5
• 70% of children have spontaneous remission before adolescence
• 77% concordance rate for monozygotic twins; 15% for dizygotic
• Asthma develops in approx 30% and allergic rhinitis in 35% of children with AD
Clinical Manifestations (J Allergy Clin Immunol 2006;118:152)
• Infantile stage (infancy–2 yo)
• Location: Cheeks, forehead, scalp, may spread to trunk
• Intensely pruritic, erythematous, scaly lesions, may have vesicles or serous exudate in severe cases
• Childhood stage (2 yo–puberty)
• Location: Flexural surfaces, wrists, ankles, hands, feet, neck, dorsum of extremities
• Less exudation; more lichenified papules and plaques
• Adult stage (puberty+)
• Location: Flexural surfaces, face, neck, upper arms, back, hands, feet
• Dry, scaly erythematous papules & plaques; lichenified plaques in areas of chronicity
• W/ severe cases, any area involved, but axillary, groin, & gluteal areas usually spared
• Complications: Bacterial or viral superinfxn of eczematous sites (e.g., eczema herpeticum)
Diagnostic Studies (N Engl J Med 2005;352:2314)
• Clinical criteria: Evidence of itchy skin + 3 of the following:
• H/o involvement of skin creases
• H/o generally dry skin in the past year
• H/o asthma or hay fever (or FHx atopy in 1st-degree relative for pts <4 yo)
• Onset of sx at <2 yo (criterion not used if child <4 yo)
• Dermatitis of flex surfaces (or cheeks/forehead/outer aspects of ext for pts <4 yo)
• Specific allergy testing not routinely recommended, depends on dz severity
• Ddx: Psoriasis, contact dermatitis, seborrheic dermatitis, scabies, vit def, drug rxns
Management (Pediatrics 2008;122:812, Am Fam Physician 2007;75:523)
• Eliminate exacerbating factors: Soap, hot water, abrasive materials (synthetics, wool), physiologic/emotional stress, individual-specific allergens and irritants
• Skin hydration w/ emollients even when asymptomatic: Avoid lotions (worsen xerosis via water evap); use thick creams/ointments (hydrolated petrolatum, petroleum jelly) are most effective; apply immediately after bathing
• Topical steroids: Limit to bid; only low potency on face, genital, intertriginous areas
• 1–2.5% hydrocortisone (low potency) for mild AD
• 0.1% triamcinolone (medium potency) for more severe AD
• Topical calcineurin inhibitors (1% pimecrolimus & 0.03% tacrolimus): Approved as 2nd-line Rx in kids >2 yo who respond poorly or are intolerant to topical steroids
• Adverse effects: Burning sensation of skin and irritation; should use sun protection
• Benefits: Not assoc w/ skin atrophy, safe for use on face
• FDA “black box warning” safety not clear w/ long-term/continuous use & in pts <2 yo
• Systemic tx used in severe cases: UV light, systemic immunosuppressants
• Adjunctive tx: Sedating antihistamines for pruritis – due to sedative effect (non-sedating antihistamines not effective for itch), wet dressings, bleach baths to ↓ local skin infections