Polymorphic light eruption
What is polymorphic light eruption?
Polymorphic light eruption is a common form of primary photosensitivity that mainly occurs in young adult women in temperate climates during spring and summer.
The name ‘polymorphic’ refers to the fact that the rash can take many forms, although in one individual it usually looks the same every time it appears. Polymorphic light eruption is also known as polymorphous light eruption, PLE or PMLE.
Who gets polymorphic light eruption?
PLE generally affects adult females aged 20–40, although it sometimes affects children and males (25%). It is particularly common in places where sun exposure is uncommon, such as Northern Europe, where it is said to affect 10–20% of women holidaying in the Mediterranean area. It is less common in Australasia. It has also been reported to be relatively common at higher altitudes compared to sea level.
PLE can occur in all races and skin phototypes and may be more prevalent in skin of colour than in white skin. There is a genetic tendency to PLE, and it is sometimes associated with or confused with photosensitivity due to lupus erythematosus (which generally is more persistent than PLE).
What causes polymorphic light eruption?
Genetic factors may be important with many affected individuals reporting a family history of PLE. Native Americans have a hereditary form of PLE (actinic prurigo).
PLE is caused by a delayed hypersensitivity reaction to a compound in the skin that is altered by exposure to ultraviolet radiation (UVR). UVR leads to impaired T cell function and altered production of cytokines in affected individuals. There is a reduction in the normal UV-induced immune suppression in the skin. This has been suggested to be either due to oestrogen or deficiency of vitamin D.
The rash is usually provoked by UVA (in 90%). This means the rash can occur when the sunlight is coming through window glass, and that standard sunscreens may not prevent it. Occasionally, UVB and/or visible light provoke PLE.
What are the clinical features of polymorphic light eruption?
PLE may be a rare occurrence in the individual concerned or may occur every time the skin is exposed to sunlight. In most affected individuals, it occurs each spring, provoked by several hours outside on a sunny day. If further sun exposure is avoided, the rash settles in a few days and is gone without a trace within a couple of weeks. It may or may not recur next time the sun shines on the skin. However, if the affected area is exposed to more sun before it has cleared up, the condition tends to get more severe and extensive.
The arms, the back of the hands, the V of the neck, the chest and lower legs/feet may be affected, but the face is usually spared. A few people complain of ocular and/or lip lesions. Juvenile spring eruption is a variant of PLE that is confined to the ears of children (usually boys).
The commonest variety of PLE presents as crops of 2–5 mm pink or red papules. Other presentations include:
- Erythema (red macules)
- Erythematous plaques
- Dry, red patches or plaques (dermatitis)
- Vesicles (blisters)
- Pinpoint papules (especially in skin of colour)
- Lichenoid plaques
- Target lesions (bull's-eye appearance)
- Prurigo confined to exposed areas
PLE persists for several days, and often longer if the affected skin is exposed to more sunlight. It resolves without scarring.
PLE usually causes a burning sensation or itch. A few individuals also report fever and malaise following sun exposure.
PLE can be the first sign of lupus erythematosus, but this is not usually the case.
Complications from polymorphic light eruption
Severe PLE can lead to emotional distress, anxiety and depression.
How is polymorphic light eruption diagnosed?
PLE is diagnosed clinically by its typical onset within hours of exposure to sunlight, and clearance after a few days. The rash is confined to exposed sites, and is often composed of erythematous papules and plaques.
Sometimes a skin biopsy is necessary to make a diagnosis. PLE has characteristic histopathological features, with upper dermal oedema and a dense perivascular lymphocytic infiltrate. Eczematous changes may be present. Direct immune fluorescence is negative, unless the patient has cutaneous lupus erythematosus.
It is usual to have a blood count and a check for circulating antinuclear antibodies (ANA) and extractable nuclear antigens (ENA) in case of photosensitive cutaneous lupus erythematosus.
Phototesting is not usually carried out, but provocation tests of exposure to UVA daily for 3 days to a small area of skin can confirm the diagnosis.
How can polymorphic light eruption be prevented?
It is not known how to prevent PLE altogether. However, many people can avoid developing a rash by using effective sun protection during the middle hours of the day during summer. In New Zealand, patients are advised to dress up during the hours indicated by NIWA's National Climate Database regional Sun Protection Alert, when the UV index is > 3.
- Cover affected areas with densely woven sun protective clothing. Choose UPF 40+ clothing where available.
- Apply SPF 50+ semi-opaque sunscreen frequently to all uncovered skin.
- Stay in the shade.
Some people with PLE successfully manage to gradually harden their skin by slowly increasing how long they spend outdoors with uncovered skin, starting with a few minutes exposure during spring.
What is the treatment for polymorphic light eruption?
The following treatments may reduce the severity of PLE:
- Topical corticosteroid creams to relieve symptoms
- Short course of oral steroids, eg to cover a summer holiday
- Phototherapy: UVB narrowband UVB, or PUVA for several weeks in early spring.
What is the outlook for polymorphic light eruption?
In most individuals, there is a hardening as the summer progresses and more sun can be tolerated without a rash appearing. This does not always occur, and some very sensitive individuals even develop PLE in the winter.
It has been noted that PLE appears to be less frequent and severe in women after the menopause.