Dermatitis, Atopic

Description

• A chronic, relapsing, pruritic eczematous condition affecting characteristic sites
• Early onset cases have coexisting allergen sensitization more often than late onset.
• Clinical phenotypical presentation is highly variable, suggesting multifactorial pathophysiology.
• May have significant effect on quality of life for patient and family—similar to that of psoriasis

Epidemiology

• 45% of all cases begin in the first 6 months of life with 95% onset prior to age 5 years.
• 70% of affected children will have a spontaneous remission before adolescence.
• Incidence on the rise for the past 3 decades in industrialized countries; overall, affects ~15% of children at some time (United States)
• Also, may have late-onset dermatitis in adults or relapse of childhood condition—primarily hand eczema
• Asians and blacks are affected more often than whites.
• 60% if one parent is affected; rises to 80% if both parents are affected

Etiology and Pathophysiology

• Two main hypothesis: immunologic with unbalanced immune response and/or skin barrier dysfunction (1)
• Alteration in stratum corneum results in transepidermal water loss and defect in barrier function.
• Epidermal adhesion is reduced either as a result of (i) genetic mutation resulting in altered epidermal proteins or (ii) defect in immune regulation causing an altered inflammatory response.
• Interleukin-31 (IL-31) upregulation is thought to be a major factor in pruritus mediated by cytokines and neuropeptides rather than histamine excess.

• Recent discovery of association between atopic dermatitis (AD) and mutation in the filaggrin gene (FLG), which codes for a skin barrier protein (2)
• Both epidermal and immune coding likely involved

Risk Factors

• “Itch–scratch cycle” (stimulates histamine release)
• Skin infections
• Emotional stress
• Irritating clothes and chemicals
• Excessively hot or cold climate
• Food allergy in children (in some cases). Studies of breastfeeding conveying decreased risk versus increased risk are mixed in conclusion (3)[C].
• Exposure to tobacco smoke
• Family history of atopy
  • Asthma
  • Allergic rhinitis

Commonly Associated Conditions

• Food sensitivity/allergy in many cases
• Asthma
• Allergic rhinitis
• Hyper-IgE syndrome (Job syndrome)
  • AD
  • Elevated IgE
  • Recurrent pyodermas
  • Decreased chemotaxis of mononuclear cells