Question from practice: A rash caused by spring sunshine
A. Given that this is the woman’s first experience of this type of rash and taking into account the other details, a likely diagnosis is polymorphic light eruption (PLE), a type of primary photodermatosis.1 The trigger for PLE is UV radiation, both UVA and UVB. More people are affected by UVA radiation2 and it is possible for an eruption to develop from behind glass (eg, when driving).
First recognised in 1817 when the term “eczema solare” was used, PLE is now thought to affect between 10 and 20 per cent of people in Central Europe, Scandinavia and the US.3 It normally first presents between the ages of 20 and 40 years and some evidence suggests a genetic component, with studies reporting that a family history of the condition is present in nearly half of patients.
It is interesting that PLE is two to three times more common in women than in men, and although it affects all skin types, it occurs more frequently in fair-skinned individuals.
Papule Small (<5mm) solid elevation of the skin.
Papulovesicle A papule that has changed into a blister.
Plaque Raised patch, resulting from the enlargement or merging of papules.
Although the exact mechanism remains a mystery, it has been speculated that PLE is the result of an immune reaction to a component in the skin which is activated after exposure to UV radiation, hence the development of an inflammatory rash.
The predominant symptom is itchy, burning skin lesions, which present on sun-exposed areas but the face is often spared. The lesions develop several hours or days after exposure to sunlight (particularly after a period when the skin has not been exposed to the sun) but as little as 30 minutes’ exposure seems to be sufficient. Initially, red patches develop which become itchy, followed by the development of the lesions.
The term “polymorphic” describes the fact that the condition can present with a range of different lesions, including papules (the most common presentation) papulovesicles and plaques (see Glossary). A mixture of lesions can occur in an individual, although this tends to be uncommon.
In people with skin type IV (African-American) PLE can present as pinpoint papules.5
PLE is different from heat rash, which is caused by sweat and affects sun-exposed and non-sun-exposed areas. One study of chronic PLE sufferers found that the condition initially presented at a single sun-exposed site but affected areas increased in subsequent years.6
PLE can have a negative impact on well-being, with one survey finding that 40 per cent of sufferers experienced emotional distress.7 The eruption normally first appears in the spring although it can occur during the winter, particularly if exposed to strong sunlight or light reflected from snow. Once an individual is affected, he or she will tend to experience repeated episodes every year. Although the condition is chronic, some evidence suggests that it clears with age.
Diagnosis is usually clinical but a GP might request investigations to exclude diseases such as systemic lupus erythematosis (rare).
In the absence of further exposure to sunlight, the condition tends to resolve without treatment or adverse effects, such as scarring, within a few days. Re-exposure to sunlight when the lesions are present will result in a worsening of the condition.
Treatment of acute PLE can be undertaken with either topical steroids or antihistamines. It should be remembered that some antihistamines (eg, promethazine) are phenothiazines, which can cause phototoxicity. In more severe cases, oral steroids have been found to be effective.
Another strategy, particularly for more severe cases, is termed “photohardening”. This endeavours to induce tolerance to UV radiation using prophylactic light therapy. Gradually exposing the whole body to both UVA and UVB in a controlled environment aims to acclimatise the skin to sunlight. Photohardening can be undertaken in specialist centres before spring and is repeated each year.
Some evidence exists for other treatments, including hydroxychloroquine, nicotinamide, beta-carotene, omega-3 polyunsaturated fatty acids and topical mixtures of antioxidants. However, none is particularly satisfactory and further study is required.
- Polymorphic light eruption (PLE) is an itchy rash (usually papular) which is triggered by exposure to sunlight.
- Treatment options for an acute eruption include topical steroids or antihistamines. Severe cases may be treated with oral steroids.
This patient is experiencing some discomfort. Because the rash is limited to her arms either a mild to moderate topical steroid or an oral antihistamine would be an appropriate first-line treatment. It would be sensible to advise her that PLE is a chronic condition which she may experience each year but gradual exposure to sunlight may induce tolerance and the condition is likely to resolve as the year progresses.
Many patients with PLE find that their tolerance with subsequent exposure to sunlight develops to such an extent as to allow them to sunbathe. This is likely to account for the fact that PLE tends to be more frequent during the spring than during the summer months when solar radiation is more intense.
Preventive measures involve sun protection, such as wearing protective clothing and applying broad spectrum sunscreens that are able to filter out both UVA and UVB light.
About the author
Rod Tucker, PhD, MRPharmS, is a pharmacist with a special interest in dermatology
Citation: The Pharmaceutical Journal DOI: 10.1211/PJ.2013.11118092
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