Contact dermatitis

Contact dermatitis
- Types
  - Important types
    - Allergic contact dermatitis
    - Irritant contact dermatitis
    - Phototoxic contact dermatitis
    - Photoallergic contact dermatitis
  - Not so important types
    - Seborrheic dermatitis
    - Infectallergic dermatitis
    - Perioral dermatitis
    - Stasis dermatitis
- Clinical features (rash)
  - Acute
    - “Sunburn type”
      - Erythema
      - Oedema
      - Vesicles
      - Urtica
      - Pruritus
    - “Exanthema type”
      - Macule
      - Papule
      - Plaque
      - Wheal
  - Subacute
    - Erythema
    - Fissure
    - Scaling
  - Chronic
    - Hyperkeratosis
    - Fissure
    - Scaling
    - Lichenification
- Diagnosis
  - Patch test
    - Contains haptens in patches which are applied to the back
    - Reading at 48, 72, 168 hours
    - Contains common haptens according to European and local standards
      - Cosmetic ingredients
      - Plants
      - Metals
      - etc.
    - + = erythema, oedema
    - ++ = papule, vesicle
    - +++ = bulla, erosion, ulcer
    - Crescendo – reaction worsens with time
      - Typical for allergic contact dermatitis
    - Decrescendo – reaction improves with time
      - Typical for irritant contact dermatiti
- Treatment
  - Identification of cause
  - Topical
    - Emollients (moisturizers)
    - Corticosteroids
    - Calcineurin inhibitors
  - Systemic
    - Antihistamines
    - Corticosteroids
Allergic contact dermatitis
- Etiology
  - Poison ivy
  - Nickel
  - Chromium
  - Perfumes
  - Soaps
  - Cosmetics
  - Tattoos
  - Latex
  - Rubber
  - Topical medications
    - Budesonid
- Pathomechanism
  - Type IVa hypersensitivity
  - Mediated by a hapten, which binds to an endogenous protein and becomes an immunogenic allergen
  - The body is sensitized to the allergen upon first contact
  - With repeated contact a rash develops
Irritant contact dermatitis
- Etiology
  - Solvents – remove lipids in the stratum corneum
    - Like alcohol
  - Acids, bases, salts – destroy proteins in the stratum corneum
  - Dust – mechanically destroys stratum corneum
  - Excessive hand washing
  - Mineral oils
  - Detergents
  - Metals
  - Dry air
  - Warm air
  - Cold air
- Pathomechanism
  - Not immune-mediated
  - Due to direct irritation -> leads to damage of stratum corneum
  - -> release of inflammatory mediators
Phototoxic contact dermatitis
- More common than photoallergic type
- Etiology
  - Topical
    - Bergamot
    - Psoralen (in plants)
    - Tar
  - Systemic
    - Tetracycline
    - Sulphonamides
    - Quinolones
    - HCTZ
- Pathomechanism
  - UV radiation converts a photosensitive molecule into a cytotoxic one
- Only occurs on sun-exposed skin
- Phototoxic contact dermatitis is exploited in psoralen-UVA (PUVA) treatment
Photoallergic contact dermatitis
- Less common than phototoxic type
- Etiology
  - PABA
  - Perfumes
  - Aromatic oils
  - Benzocaine
- Pathomechanism
  - UV radiation converts a photosensitive molecule (a photoallergen) into an allergen -> type IV hypersensitivity
- Only occurs on sun-exposed skin