Photodermatoses

Photodermatoses – skin diseases that develop due to light exposure
Photodermatoses of unknown origin
- Solar dermatitis = sunburn
  - UVB radiation causes apoptosis of keratinocytes -> release of inflammatory cytokines
  - Clinical features
    - Pruritus, pain
    - Erythema, oedema
    - Blisters (severe)
  - Treatment
    - Wet compress
    - Cooling ointments
    - Topical steroids
- Polymorphous light eruption (PLE)
  - Chronic disease
  - In adult females
  - Most common photodermatitis
  - Clinical features
    - Itching, burning erythema
    - Malaise, headache
- Solar urticaria
  - Rare
  - Type I hypersensitivity
  - Urtica at site of sun exposure
- Actinic prurigo
- Chronic actinic dermatitis
Photodermatoses of known origin
- Phototoxic reactions
- Photoallergic reactions
Diagnosis
- Photo-patch test
  - UVA applied, then patch
  - Read immediately, then at 24, 48, 72 hours
- Photo-provocation test
  - Differentiate between solar urticaria, chronic actinic dermatitis, polymorphous light eruption, SLE
Treatment
- Photohardening
- Photoprotection

Phototherapy

Indications
- Psoriasis
- Atopic dermatitis
- Alopecia areata
- Granuloma annulare
- Cutaneous T-cell lymphoma
- Vitilligo
- Photodermatoses
- BCC
- Actinic keratosis
Mechanisms
- Thickens epidermis
- Hyperpigmentation
- Immunosuppressive effect
- Anti-tumor effect
Procedure
- Minimal erythematous dose (MED) is determined
- The dose of UV light depends on the MED
Types
- Narrow-band UVB
- Broad-band UVB
- Selective UVB
- Psoralen + UVA
- Photodynamic therapy
  - Uses visible light, not UV
  - For cancers that are caused by UV (BCC)