follow @PCDSUKCreated: 9th October 2011 | Last Updated: 21st January 2013
Introduction
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Photodermatoses are a group of skin conditions associated with an abnormal reaction to UV (ultraviolet) radiation. Whereas UVB is the predominant factor in sunburn, UVA is largely responsible for the photodermatoses. Photodermatoses can be split into two groups:
This chapter provides an introduction to the photosensitive dermatoses and is set out as below (more detail about the individual photosensitive conditions can be found in the relevant chapters): |
Aetiology
The photosensitive dermatoses can be divided by their aetiology as follows:
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Idiopathic
- Polymorphic light eruption (PLE)
- Actinic prurigo
- Chronic actinic dermatitis
- Solar urticaria
- Hydroa vacciniforme
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Genetic
- Xeroderma pigmentosum
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Metabolic
- Porphyria
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Exogenous
- Drug-induced photosensitivity
- Photocontact allergic reactions
- Phytophotodermatitis
History
- Age and sex - genodermatoses such as xeroderma pigmentosum are usually apparent in childhood, polymorphic light eruption (PLE) usually has an onset in later childhood and is more commonly seen in woman, chronic actinic dermatitis is mainly a disorder of older men
- Timing of the eruption in relation to sun exposure / use of sunscreen - solar urticaria occurs within minutes, PLE many hours. Patients with chronic actinic dermatitis or porphyria cutanea tarda may not be aware that their symptoms are worse in the sun. Symptoms made worse after application of sunscreen suggest a photocontact allergic dermatitis to the sunscreen
- Timing of the eruption in relation to season - PLE is typically prominent in the Spring and improves later in the Summer
- Pain - most photosensitive rashes cause itch. A burning pain is typical for erythropoieitc protoporphyria
- Window glass - most glass only blocks UVB, whereas laminated windows (eg in some front car windscreens) also protect against UVA
- Medications - ask about all prescribed and OTC drugs, systemic and topical. Always enquire about quinine
- Family history - important for the porphyrias
Clinical findings
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Distribution
- Photosensitive dermatoses mainly (but not exclusively) affect the UV-exposed areas of the skin
- The classical presentation of several of the photosensitive rashes (eg drug-induced, chronic actinic dermatitis) is that there will be relative sparing of shaded areas of the face (lower eyelids, beneath the nose, behind the ears and under the chin) in comparison with airborne contact allergic dermatitis, which is not a photosensitive disorder and does not spare UV-protected areas. However, the diagnosis is not always clear cut as patients with more severe / chronic forms of photosensitive dermatoses may not have sparing of UV-protected areas of the face
- Involvement of the dorsal aspects of the hands is more patchy
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Morphology
- Scale - if the rash heals with scaling it is more likely to represent an eczematous eruption (eg drug-induced or chronic actinic dermatitis) as opposed to PLE or solar urticaria
Images
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Figure: 1
Photosensitive distribution |
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Figure: 2 Drug-induced photosensitivity Note the relative sparing of photo-protected areas |
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Figure: 3 Airborne contact dermatitis to sesquiterpene lactones in plants Sesquiterpene lactones are allergens found in the compositae species of plants such as dandelions and chrysanthemums. They are not photosenitising agents but instead cause an allergic contact dermatitis. The rash does not spare photoprotected areas |
Investigations
- If lupus needs to be excluded, check bloods - FBC, PV, routine biochemistry, ANA and ENA (specifically Ro and La antibodies, which can be present even if ANA is negative)
- Porphyria - refer to the chapter on porphyria
- Phototesting - can help diagnose photosensitive rashes where there is diagnostic uncertainty. It can also be of use in assessing some patients with moderate to severe photosensitive dermatoses to aid management
- Photopatch testing - is of use for patients suspected of having a photocontact allergic dermatitis to sunscreen. The only other relevant topical preparations that could give to such a reaction are the NSAID
Management
- Refer to relevant chapters
- It is important to bear in mind that sunscreens are much more effective against UVB than UVA - patients need to be advised to use a high factor sunscreen (protects against UVB) with a 4 or 5 star rating (protects against UVA). Click here for a patient information leaflet on UV protection