Eczema is a chronic inflammatory disorder of the skin characterised by dermal inflammation (dermatitis) with resultant spongiotic change in the epidermis histologically, with chronic features including epidermal acanthosis, hyperkeratosis, and parakeratosis

Aetiology

• Affects up to 25% of school aged children

Pathophysiology

• Eczema is a combination of decreased skin barrier function, environmental factors and immunology
• Impairment of skin barrier function is a key factor - mutations in fillagrin gene
  • Filament aggregating protein - ↓AMP in skin
  • Specifically associated with severe/early onset disease (ichthyosis vulgaris)
• The defective skin barrier allows access/sensitisation to allergen and promotes colonisation by microorganisms
• Dermatitis triggers the disease process
  • The normal dermis has a small amount of lymphocytes and other immune cells but in skin with eczema there is a vast infiltrate visible
  • TH2 cells, DC, and macrophages and mast cells are involved - probably attracted to lesions by stressed keratinocytes
• Keratinocytes in the epidermis start detaching from one another, becoming rounder and the intercellular spaces widening between them
• If the eczema has come on acutely, this separation may be so severe that vesicles form
  • Under the microscope, this makes the epidermis look like a sponge, hence 'spongiotic' change
• Environmental factors - Koebner phenomenon, infection, drugs

Clinical features

• Childhood predominance: symptoms tend to become less severe with age
• Associated with atopic phenotype: asthma, hayfever, raised eosinophils
• In infants, the face is a common site
• In older children/adults, the antecubital fossa and posterior knee (flexor surfaces) are affected
• The skin is itchy, erythematous, and oozing
• There may be vesicles, which may have crusted over
• Eventually, the skin becomes dry and flaky
• Repeated scratching causes lichenification (thick, leathery skin, also called lichen simplex et chronicus