Photosensitive Eruptions (Photodermatoses)

History

• When approaching a possible case of photodermatosis, take a full history, noting particularly the timing of the rash after exposure, any seasonal differences, type of discomfort or pain (eg. itching or severe burning compared with a typical case of sunburn).
• How much of exposure is required to trigger symptoms; and does it still occur in spite of protection with sun cream and/or is it blocked by glass (which blocks UVB)?
• Take a full medication history - including topical skin applications and drugs such as quinine (a known photosensitiser) - not always considered as drugs by patients.
• Has there been use of perfumes, or contact with airborne sensitisers or plants?
• Is there a past history or significant family history?

Examination

• Which areas are affected and which spared? Sparing of face skin creases, behind the ears, lower eyelid and beneath nose strongly suggests photosensitivity - although chronic photosensitivity can extend to shielded areas. ¹
• Consider the type of rash - wheals suggest solar urticaria, sheet like erythema suggests drug phototoxicity, blisters can occur in any severe photosensitivity, but suggest Porphyria Cutanea Tarda or reactions to plants.

Phototesting with UV light, patch tests and the combination (photopatch) are occasionally helpful when there is diagnostic difficulty.
Photodermatoses are broadly classified into the four groups based on aetiology:

• Polymorphic Light Eruption (PLE) - Commonest photodermatosis, F:M=2:1 Variable severity. ~10% of adolescents and young adults will suffer to some degree at some time.
  • Presents with itchy papules, eczematous plaques and vesicles, often with some urticaria initially.
  • These develop about 24 hours after exposure to sunlight. In the UK this can start in the spring and continue through to autumn although many case will have progressively fewer problems as spring turns to summer - their skin seems to "harden" with continued exposure.
  Management:
  • Simple avoidance measures may be enough - shade, clothing, sunscreens.
  • An acute eruption can be treated with emollients and mild to moderate potency topical steroids.
  • Severe cases may benefit from short courses of PUVA in the spring to artificially "harden" the skin.^2,3
• Chronic Actinic Dermatitis (Actinic reticuloid) - A rare condition affecting mainly middle aged and elderly men - often follows years of chronic contact dermatitis.
  • Presents as lichenified plaques on light exposed skin.
  • Initially worse in the summer but can become perennial.
  • There is usually little doubt about the diagnosis, but consider the possibility of a drug induced photodermatosis or airborne contact dermatitis.
  Management
  • Light avoidance, sunscreens and topical steroids.
  • Chronic cases may require systemic steroids and/or azathioprine.
• Solar urticaria - Rare condition - wheals appear minutes after exposure to sunlight. May be confused with erythropoietic protoporphyria (especially in children).
  Management
  • Sun avoidance, sunscreens, antihistamines.
  • PUVA can be helpful.
• Actinic Prurigo Another rare condition: tends to be familial although aetiology is unclear. Affects predominantly indian females, often starts in childhood with papules and excoriation on sun-exposed skin.
  Management
  • Sunscreens, topical steroids, systemic steroids and PUVA.
• Hydroa vacciniforme (HV) Rare childhood photodermatosis with recurrent papules, vesicles and crusts occurring on sun exposure, healing with scarring, but generally resolving in adolescence.

• Chromosomal abnormalities e.g. : Porphyrias or Bloom's disease - an autosomal recessive condition primarily affecting Ashkenazi Jews.
• Defective DNA repair Examples: Xeroderma pigmentosum (XP) - a collection of several genetic variants which present in childhood with severe redness and swelling up to 72 hours after sun exposure, resulting in scarring and are very rare.

• Porphyrias
• Pellagra.

• Drugs - many can cause photosensitivity; commonly NSAIDs, tolbutamide and the sulphonylureas, frusemide and the thiazides, antibiotics (eg, Nalidixic acid, ciprofloxacin, tetracylines, sulphonamides and griseofulvin), amiodarone, cytotoxics, quinine, psoralens and phoryrins.
• Topical agents - perfumes, skin products (prescribed and OTC), sunscreens; and plant psoralens: Umbelliferae (many common plants eg hogweed, carrots and celery) and Rutaceae (Rue family eg citrus) and plant oleoresins (Compositae - daisy family).