Polymorphic Light Eruption

A polymorphic light eruption occurs in response to sunlight after a winter in which the skin has been covered and scarcely exposed to the sun. It most frequently occurs in women travelling for short periods to tropical areas during winter in northern latitudes. It is caused by UVA, UVB and visible light¹ and so it may occur when behind glass as in a car. It is thought to be caused by an immunological reaction but the precise nature is unknown. It has been suggested that 17beta-oestradiol prevents UVR-induced suppression of the contact hypersensitivity response caused by the release of immunosuppressive cytokines. This would account for its prevalence in adult women and its tendency to wane after the menopause.²

The term polymorphous indicates the variable nature of the rash but for any individual, the rash tends to be fairly constant from year to year.

• There are no reliable estimates of the incidence of this condition although it has been suggested that it affects as many as 15% of healthy people in the UK.²
• It is more common in those with fair skin and tends to affect women more often than men.
• All authors recognise that it is more common in women but they disagree about the scale. Emedicine gives a female preponderance of 2 or 3 times but states that this may be an overestimate as women are more likely to present to a doctor³ whilst DermnetNZ implies a much greater female preponderance stating that "it sometimes affects children and rarely males."⁴
• Onset is usually before the age of 30 but tends to be later in men than women.
• It is not thought to be genetic but around 15% give a family history of the disease.

It usually presents in the spring when bodies that have been covered all winter are again exposed to the sun. However, foreign travel to distant shores and possibly reflected light whilst skiing may permit it to present in the winter. It may be an occasional occurrence but for most sufferers it is an annual event each spring.

• The eruption typically starts at the beginning of a holiday in a sunny place or at a high altitude.
• Exposure of between half an hour and several hours is required to initiate the eruption.
• The usual presentation is crops of 2-5 mm pink macular or papular spots on the arms, upper chest or lower legs, but the face is usually spared.
• Other presentations include vesicles followed by dry red patches. There can be target lesions, resembling erythema multiforme.
• There is often pruritus but there may be a burning or stinging pain.
• There is occasionally a systemic flu-like illness.
• It tends to subside over the next week if there is no further exposure.

Variant

It is usually a problem of people with fair skin but in black people, there is a variant with pinpoint papules, 1 or 2 mm in diameter on sun-exposed areas, sparing the face and flexural surfaces.⁵

• Lupus erythematosis
• Erythropoietic porphyria
• Drug eruption
• Photosensitivity reaction.

Usually the diagnosis is clinical but investigations may be requested to exclude other diseases such as SLE or porphyria. Antinuclear antibody (ANA), anti-Ro (SS-A), and anti-La (SS-B) tests, as well as urine, stool, and blood porphyrin levels, may be requested.

Other tests may include photopatch testing and biopsy but they are not performed as a routine.

It is said that a polymorphic light eruption may be the first sign of systemic lupus erythematosis or discoid lupus erythematosis but this is very uncommon.

• For treating the acute condition, topical steroids are of value but a short course of oral steroids may be required.
• Antihistamines may help pruritus. The older type are more effective as the benefit is related more to the sedative than the antihistamine effect but phenothiazines can also cause photosensitivity.

Most of management aims at prevention rather than cure and simple measures are usually adequate.⁶

• The rash usually moderates as the summer advances and graduated exposure to sunlight may acclimatize the skin and prevent the rash.
• At times of risk, covering the skin is beneficial. Many materials are not totally impervious to sunlight.
• Sunscreens are beneficial but incompletely so as they do not usually filter out UVA.
• Prophylactic UVB therapy before the start of the season may be of value.¹
• Systemic vitamin C or vitamin E is of no value.⁷
• Adding an antioxidant to a sunscreen increases its benefit considerably.⁸ This appears to be a significant advance but at the time of writing no such formulation appears in the BNF.
• Betacarotene and hydroxychloroquine can both improve tolerance to the sun.⁹
• In a number of dermatoses in which there is an immunological component, there is increasing interest in the use of thalidomide.¹⁰ It should be used only as part of a research protocol.

The condition is likely to ease as the spring and summer advance but it will probably recur the following year unless steps are taken. It may even become worse with succeeding years. A natural fall in oestrogens may account for the tendency to remit after the menopause.²

Prevention has been discussed under management. Graduated exposure to sunlight, sun blockers and appropriate clothes are all of value.