Polymorphic light eruption
What is polymorphic light eruption?
Polymorphic or polymorphous light eruption (PMLE) is a common rash that occurs in exposed to sunlight, as a result of photosensitivity.
The name ‘polymorphic’, or ‘polymorphous’ refers to the fact that the rash can take many forms, although in one individual it usually looks the same every time it appears.
Who gets PMLE?
Polymorphic light eruption generally affects adult females aged 20 to 40, although it sometimes affects children and rarely males. It is more common in places where sun exposure is uncommon, such as Northern Europe, where it is said to affect 10% of women holidaying in the Mediterranean.
What are the clinical features of PMLE?
The commonest variety of PMLE presents as crops of 2-5 mm pink or red raised spots on the arms. Other areas may be involved, particularly the back of the hands, the chest and lower legs, but the face is usually spared. The rash persists for several days, and often longer if the affected skin is exposed to more sunlight.
Sometimes the rash looks like dermatitis, i.e. there are larger dry, red patches that may be blistered. Occasionally there are target lesions (bull's-eye appearance).
PMLE usually causes a burning sensation or itch.
Juvenile spring eruption
Juvenile spring eruption is a variant of PMLE that is confined to the ears.
What is the cause of PMLE?
PMLE is thought to be caused by an immune reaction to a compound in the skin which is altered by exposure to ultraviolet radiation. It is usually provoked not only by short wavelength UVB but also by longer wavelength UVA. This means the rash can occur when the sunlight is coming through window glass, and that sunblocks may not be all that effective at preventing it.
PMLE may be a rare occurrence in the individual concerned or may occur every time the skin is exposed to sunlight. In most, 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.
PMLE can be the first sign of lupus erythematosus, but this is not usually the case.
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 PMLE in the winter.
How is PMLE diagnosed?
PMLE 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 tends to be erythematous papules and plaques. Sometimes a skin biopsy is necessary to help make a diagnosis. PMLE has characteristic histopathological features.
How can PMLE be prevented?
It is not known how to prevent PMLE 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, dress up during the hours indicated by the Metservice's regional Sun Protection Alert.
- 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.
Many patients find antioxidant nutritional supplements helpful. These include Polypodium leucotomas (Heliocare™), beta carotene and astaxathanin, also a carotene.
Some people with PMLE 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 PMLE?
The following treatments may reduce the severity of PMLE:
- Topical corticosteroid creams to relieve symptoms
- Short course of oral steroids e.g. to cover a summer holiday
- Phototherapy: UVB or PUVA for several weeks in early spring.
On DermNet NZ:
- Polymorphic light eruption – pathology
- Cutaneous lupus erythematosus
- Jessner lymphocytic infiltrate
- Juvenile spring eruption
- Polymorphous light eruption – Medscape Reference
- Polymorphic Light Eruption – British Association of Dermatologists
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