Assessment

History

When assessing someone with a possible photodermatosis, take a full history, noting particularly:

• The timing of the rash after sun exposure?
• Any seasonal differences?
• Type of discomfort or pain (eg itching or severe burning compared with a typical case of sunburn)?
• How much exposure is required to trigger symptoms?
• Does it still occur in spite of protection with sun cream and/or is it blocked by glass (which blocks ultraviolet B (UVB))?
• Take a full medication history, including topical skin applications and drugs such as quinine (a known photosensitiser) which are 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 of skin are affected and which spared? Sparing of face skin creases, behind the ears, lower eyelids and beneath the 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.

Investigations

• Phototesting with ultraviolet (UV) and sometimes visible light, patch tests and the combination (photopatch) are occasionally helpful when there is diagnostic difficulty. In photopatch testing, suspected photoallergens are applied in two sets. One set is removed after 24 hours and UV irradiation follows.
• Serological tests may help to exclude connective tissue disease.
• Testing to exclude metabolic causes may be helpful, eg plasma porphyrin levels.

Idiopathic photodermatoses

Polymorphic light eruption (PALE)

The most common photodermatosis. Females are affected twice as frequently as males. About 15% of adolescents and young adults will suffer to some degree at some time. Please also refer to the separate article Polymorphic Light Eruption for further details.

• Presentation:
  • Itchy papules, eczematous plaques and vesicles, often with some urticaria initially. Variable severity. 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 people 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. Oral steroids are sometimes needed. Antihistamines may help pruritus.
  • Severe cases may benefit from short courses of psoralen and UVA treatment (PUVA) in the spring to artificially 'harden' the skin.^[2][3] There is a separate article describing PUVA.

Chronic actinic dermatitis (actinic reticuloid)

A rare condition affecting mainly middle-aged and elderly men. It often follows years of chronic contact dermatitis.

• Presentation:
  • Lichenified plaques on light-exposed skin.
  • It is initially worse in the summer but can become perennial.
  • There is usually little doubt about the diagnosis; however, 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

A rare condition.

• Presentation:
  • Wheals appear minutes after exposure to sunlight.
  • There is associated pruritus, stinging and erythema.^[4]
  • It usually affects exposed skin but may also appear on unexposed areas if thin clothing is worn.
  • There may be mucosal involvement with tongue and lip swelling.
  • The rash disappears after sun exposure ceases and this is key to diagnosis.
  • An immune-mediated reaction has been proposed.^[4]
  • May be confused with erythropoietic protoporphyria (especially in children) and polymorphous light eruption. The latter is more common but it takes longer for the lesions to subside.^[4] It tends to be a chronic disease.^[5]
• Management:
  • Sun avoidance, sunscreens, antihistamines.
  • PUVA can be helpful, as well as phototherapy with UVA or UVB and photochemotherapy. Desensitisation treatments may be carried out in spring but effects may be short-lived and maintenance treatment may be needed.^[4]

Actinic prurigo

Another rare condition. Tends to be familial, although aetiology is unclear. It rarely occurs in Europe and Asia but is seen more commonly in Central and South America.^[6]

• Presentation:
  • It often presents in childhood, with papules and excoriation on sun-exposed skin
  • Conjunctivae and lips can be affected.
• Management:
  • Sunscreens, topical steroids, systemic steroids and PUVA. Antimalarials and thalidomide may also be used.^[6]

Hydroa vacciniforme

A rare childhood photodermatosis with recurrent papules, vesicles and crusts occurring on sun exposure, and healing with scarring. It generally resolves in adolescence.

Genetic photodermatoses

Chromosomal abnormalities

Includes:

• Cutaneous porphyrias.
• Bloom's syndrome - a rare chromosome breakage syndrome, primarily affecting Ashkenazi Jews. It presents with failure to thrive, stunted growth, small and narrow facies, sun-sensitive facial telangiectasiae, immunodeficiency, and increased risk of malignancies.^[7]

Defective DNA repair

Includes:

• Xeroderma pigmentosum - 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. Very rare.

Other

Includes:

• Subacute cutaneous lupus erythematosus - this can occur in people with systemic lupus erythematosus (SLE), Sjögren's syndrome, and complement deficiency, or it may be drug-induced. It is a photosensitive dermatitis that affects those who are genetically predisposed (HLA-B8, HLA-DR3, HLA-DRw52, HLA-DQ1).^[8] Females are more commonly affected. Papules occur in sun-exposed areas and tend to develop into annular erythema or produce a psoriasis-like rash. Scarring is not typical. There may be associated arthralgia, arthritis and fatigue. Other symptoms of SLE and Sjögren's syndrome may be present. Management includes sunscreens, protective clothing, corticosteroids and antimalarials. Other potential treatments include thalidomide, retinoids, interferon and immunosuppressants.^[8]

Metabolic photodermatoses

• Porphyrias - see separate article Porphyrias which provides more detail.
• Pellagra - see separate article Pellagra which provides more detail.

Exogenous photodermatoses

Drug-induced photosensitivity

• Photosensitivity reactions can occur as adverse effects of some commonly prescribed topical or systemic medications.^[9]
• Reactions can be phototoxic (where the damage to the tissues is direct), or photo-allergic (where the damage is immunologically mediated).^[9]
• Lichenoid reactions, subacute cutaneous lupus erythematosus or pseudoporphyria can also occur. Commonly implicated medications include:^[10]
  • Antibiotics - tetracyclines, fluoroquinolones, sulphonamides.
  • Non-steroidal anti-inflammatory drugs (NSAIDs).
  • Diuretics - eg furosemide, bumetanide.
  • Sulphonylureas.
  • Neuroleptics - eg phenothiazines.
  • Antifungals - eg terbinafine, itraconazole, voriconazole.
  • Other drugs - eg amiodarone, enalapril, oral contraceptives, diltiazem.
  • Sunscreens.
  • Fragrances.
• Presentation:^[10]
  • Phototoxic reactions tend to be more common and resemble severe sunburn. Their onset can be rapid.
  • Photo-allergic reactions tend to resemble allergic contact dermatitis and they can have delayed onset (24-72 hours).
  • Lichenoid reactions appear as erythematous papules and plaques. Hydroxychloroquine and captopril are commonly involved drugs.
  • Lupus-like reactions resembling subacute cutaneous lupus erythematosus can occur with some drugs, eg hydrochlorothiazide, calcium-channel blockers, angiotensin-converting enzyme (ACE) inhibitors and some antifungals.
  • Pseudoporphyria reactions, where the clinical picture resembles porphyria cutanea tarda but with normal porphyrin levels, can occur to drugs including naproxen.
• Management:
  • Topical corticosteroids, systemic if severe.
  • Sunscreens (if they are not the cause of the photosensitivity).
  • Avoidance of the causative agent.
• Complications of repeated phototoxic injury include premature skin ageing and increased risk of skin cancer.^[10]

Phytophotodermatitis^[11]

• This is a photosensitivity reaction caused by exposure to certain plants (either ingestion or skin contact) followed by exposure to sunlight. Furocoumarins (psoralens) are the plant oils involved. Common plants include:
  • Celery and parsnip
  • Giant hogweed
  • Angelica
  • Fennel, dill, parsley, anise
  • Lime, lemon, fig
  • Mustard
  • Chrysanthemums
• Perfume-induced phytophotodermatitis can also occur with perfumes that use oil of bergamot.
• Presentation:
  • Burning erythema and blistering about 24 hours after exposure. Pruritus is not usual.
  • Desquamation and hyperpigmentation can occur.
  • Usually self-limiting.
• Management:
  • Avoidance of plants/sunlight.
  • Topical steroids (systemic if severe) and NSAIDs.
  • 4% hydroquinone cream may reduce hyperpigmentation but dermatology guidance is advised.